![Human Body](https://upload.wikimedia.org/wikipedia/commons/d/d2/Human_body.jpg)
Sex differences in human physiology are distinctions of physiological characteristics associated with either
male
Male (symbol: ♂) is the sex of an organism that produces the gamete (sex cell) known as sperm, which fuses with the larger female gamete, or ovum, in the process of fertilization.
A male organism cannot reproduce sexually without access to ...
or
female
Female (Venus symbol, symbol: ♀) is the sex of an organism that produces the large non-motile ovum, ova (egg cells), the type of gamete (sex cell) that fuses with the Sperm, male gamete during sexual reproduction.
A female has larger gamet ...
humans. These differences are caused by the effects of the different
sex chromosome
A sex chromosome (also referred to as an allosome, heterotypical chromosome, gonosome, heterochromosome, or idiochromosome) is a chromosome that differs from an ordinary autosome in form, size, and behavior. The human sex chromosomes, a typical ...
complement in males and females, and differential exposure to
gonad
A gonad, sex gland, or reproductive gland is a mixed gland that produces the gametes and sex hormones of an organism. Female reproductive cells are egg cells, and male reproductive cells are sperm. The male gonad, the testicle, produces sper ...
al
sex hormone
Sex hormones, also known as sex steroids, gonadocorticoids and gonadal steroids, are steroid hormones that interact with vertebrate steroid hormone receptors. The sex hormones include the androgens, estrogens, and progestogens. Their effects ar ...
s during development.
Sexual dimorphism
Sexual dimorphism is the condition where the sexes of the same animal and/or plant species exhibit different morphological characteristics, particularly characteristics not directly involved in reproduction. The condition occurs in most ani ...
is a term for the
phenotypic
In genetics, the phenotype () is the set of observable characteristics or traits of an organism. The term covers the organism's morphology or physical form and structure, its developmental processes, its biochemical and physiological proper ...
difference between males and females of the same species.
The process of
meiosis
Meiosis (; , since it is a reductional division) is a special type of cell division of germ cells in sexually-reproducing organisms that produces the gametes, such as sperm or egg cells. It involves two rounds of division that ultimately resu ...
and
fertilization
Fertilisation or fertilization (see spelling differences), also known as generative fertilisation, syngamy and impregnation, is the fusion of gametes to give rise to a new individual organism or offspring and initiate its development. Proce ...
(with rare exceptions) results in a
zygote
A zygote (, ) is a eukaryotic cell formed by a fertilization event between two gametes. The zygote's genome is a combination of the DNA in each gamete, and contains all of the genetic information of a new individual organism.
In multicellula ...
with either two
X chromosome
The X chromosome is one of the two sex-determining chromosomes (allosomes) in many organisms, including mammals (the other is the Y chromosome), and is found in both males and females. It is a part of the XY sex-determination system and XO sex-d ...
s (an XX female) or one X and one
Y chromosome
The Y chromosome is one of two sex chromosomes (allosomes) in therian mammals, including humans, and many other animals. The other is the X chromosome. Y is normally the sex-determining chromosome in many species, since it is the presence or abse ...
(an XY male) which then develops the typical female or male phenotype. Physiological sex differences include discrete features such as the respective male and female
reproductive system
The reproductive system of an organism, also known as the genital system, is the biological system made up of all the anatomical organs involved in sexual reproduction. Many non-living substances such as fluids, hormones, and pheromones are als ...
s, as well as average differences between males and females including size and strength, bodily proportions, hair distribution, breast differentiation, voice pitch, and brain size and structure.
Sex determination and differentiation
![YChromShowingSRY2](https://upload.wikimedia.org/wikipedia/commons/f/fb/YChromShowingSRY2.png)
:
The
human genome
The human genome is a complete set of nucleic acid sequences for humans, encoded as DNA within the 23 chromosome pairs in cell nuclei and in a small DNA molecule found within individual mitochondria. These are usually treated separately as the n ...
consists of two copies of each of 23
chromosomes
A chromosome is a long DNA molecule with part or all of the genetic material of an organism. In most chromosomes the very long thin DNA fibers are coated with packaging proteins; in eukaryotic cells the most important of these proteins are ...
(a total of 46).
One set of 23 comes from the mother and one set comes from the father.
Of these 23 pairs of chromosomes, 22 are
autosomes, and one is a
sex chromosome
A sex chromosome (also referred to as an allosome, heterotypical chromosome, gonosome, heterochromosome, or idiochromosome) is a chromosome that differs from an ordinary autosome in form, size, and behavior. The human sex chromosomes, a typical ...
.
There are two kinds of sex chromosomes–
X and
Y. In humans and in almost all other mammals, females carry two X chromosomes, designated XX, and males carry one X and one Y, designated XY.
A human egg contains only one set of chromosomes (23) and is a
haploid
Ploidy () is the number of complete sets of chromosomes in a cell, and hence the number of possible alleles for autosomal and pseudoautosomal genes. Sets of chromosomes refer to the number of maternal and paternal chromosome copies, respectively ...
. Sperm also have only one set of 23 chromosomes and are therefore haploid. When an egg and sperm fuse at
fertilization
Fertilisation or fertilization (see spelling differences), also known as generative fertilisation, syngamy and impregnation, is the fusion of gametes to give rise to a new individual organism or offspring and initiate its development. Proce ...
, the two sets of chromosomes come together to form a unique
diploid
Ploidy () is the number of complete sets of chromosomes in a cell, and hence the number of possible alleles for autosomal and pseudoautosomal genes. Sets of chromosomes refer to the number of maternal and paternal chromosome copies, respectively ...
individual with 46 chromosomes.
The sex chromosome in a human egg is always an X chromosome since a female only has X sex chromosomes. In sperm, about half the sperm have an X chromosome and half have a Y chromosome.
If an egg fuses with sperm with a Y chromosome, the resulting individual is male. If an egg fuses with sperm with an X chromosome, the resulting individual is female.
There are rare exceptions to this rule in which, for example,
XX individuals develop as males or
XY individuals develop as females.
Chromosomes are not the final determinant of sex. In some cases, for example, chromosomally female babies that have been exposed to high levels of
androgen
An androgen (from Greek ''andr-'', the stem of the word meaning "man") is any natural or synthetic steroid hormone that regulates the development and maintenance of male characteristics in vertebrates by binding to androgen receptors. This inc ...
s before birth can develop
masculinized
Virilization or masculinization is the biological development of adult male characteristics in young males or females. Most of the changes of virilization are produced by androgens.
Virilization is most commonly used in three medical and biology ...
genitals by the time they are born. There are other variations of sex chromosomes that lead to a variety of different physical expressions.
The X-chromosome carries a larger number of genes in comparison to the Y-chromosome. In humans,
X-chromosome inactivation
X-inactivation (also called Lyonization, after English geneticist Mary Lyon) is a process by which one of the copies of the X chromosome is inactivated in therian female mammals. The inactive X chromosome is silenced by being packaged into ...
enables males and females to have an equal expression of the genes on the X-chromosome since females have two X-chromosomes while males have a single X and a Y chromosome. X-chromosome inactivation is random in the somatic cells of the body as either the maternal or paternal X-chromosome can become inactivated in each cell. Thus, females are genetic mosaics.
Size and body shape
* Externally, the most sexually dimorphic portions of the human body are the chest, the lower half of the face, and the area between the waist and the knees.
* Men weigh more than women.
* On average, men are taller than women by about 10%.
* On average, men have a larger waist in comparison to their hips (see
waist–hip ratio
The waist–hip ratio or waist-to-hip ratio (WHR) is the dimensionless ratio of the circumference of the waist to that of the hips.
This is calculated as waist measurement divided by hip measurement (). For example, a person with a 30″ () ...
) than women.
*In women, the index and ring fingers tend to be either more similar in size or their index finger is slightly longer than their ring finger, whereas men's ring finger tends to be longer.
Skeleton and muscular system
Skeleton
The female skeleton is generally less massive, smoother, and more delicate than the male;
its
rib cage
The rib cage, as an enclosure that comprises the ribs, vertebral column and sternum in the thorax of most vertebrates, protects vital organs such as the heart, lungs and great vessels.
The sternum, together known as the thoracic cage, is a semi- ...
is more rounded and smaller, its
lumbar
In tetrapod anatomy, lumbar is an adjective that means ''of or pertaining to the abdominal segment of the torso, between the diaphragm and the sacrum.''
The lumbar region is sometimes referred to as the lower spine, or as an area of the back i ...
curve greater, and a generally longer and smaller female
waist
The waist is the part of the abdomen between the rib cage and hips. On people with slim bodies, the waist is the narrowest part of the torso.
''Waistline'' refers to the horizontal line where the waist is narrowest, or to the general appearan ...
results from the
chest
The thorax or chest is a part of the anatomy of humans, mammals, and other tetrapod animals located between the neck and the abdomen. In insects, crustaceans, and the extinct trilobites, the thorax is one of the three main divisions of the crea ...
being more narrow at the base, and the pelvis generally not as high.
The
pelvis
The pelvis (plural pelves or pelvises) is the lower part of the trunk, between the abdomen and the thighs (sometimes also called pelvic region), together with its embedded skeleton (sometimes also called bony pelvis, or pelvic skeleton).
The ...
is, in general, different between the human female and male skeleton.
Although variations exist and there may be a degree of overlap between typically male or female traits,
the pelvis is the most dimorphic bone of the human skeleton and is therefore likely to be accurate when using it to ascertain a person's sex.
It differs both in overall shape and structure. The female pelvis, which is adapted for
gestation
Gestation is the period of development during the carrying of an embryo, and later fetus, inside viviparous animals (the embryo develops within the parent). It is typical for mammals, but also occurs for some non-mammals. Mammals during pregna ...
and
childbirth
Childbirth, also known as labour and delivery, is the ending of pregnancy where one or more babies exits the internal environment of the mother via vaginal delivery or caesarean section. In 2019, there were about 140.11 million births globall ...
, is less high, but proportionately wider and more circular than in the male; its
sacrum
The sacrum (plural: ''sacra'' or ''sacrums''), in human anatomy, is a large, triangular bone at the base of the spine that forms by the fusing of the sacral vertebrae (S1S5) between ages 18 and 30.
The sacrum situates at the upper, back part ...
—the triangular bone at the upper posterior of the pelvic cavity, serving as the base of the spine—is also wider.
The female pelvis is tilted
anteriorly, often resulting in the more sway-backed appearance.
In females, the
acetabula
The acetabulum (), also called the cotyloid cavity, is a concave surface of the pelvis. The head of the femur meets with the pelvis at the acetabulum, forming the hip joint.
Structure
There are three bones of the ''os coxae'' (hip bone) that ...
, the concave surfaces to which the balls of the femurs attach via ligaments, are located farther apart,
which increases the distance between the most outer points of the femurs (their
greater trochanter
The greater trochanter of the femur is a large, irregular, quadrilateral eminence and a part of the skeletal system.
It is directed lateral and medially and slightly posterior. In the adult it is about 2–4 cm lower than the femoral head.Stan ...
s) and thus the width of the
hips
In vertebrate anatomy, hip (or "coxa"Latin ''coxa'' was used by Celsus in the sense "hip", but by Pliny the Elder in the sense "hip bone" (Diab, p 77) in medical terminology) refers to either an anatomical region or a joint.
The hip region is ...
.
Female
femur
The femur (; ), or thigh bone, is the proximal bone of the hindlimb in tetrapod vertebrates. The head of the femur articulates with the acetabulum in the pelvic bone forming the hip joint, while the distal part of the femur articulates with ...
s are therefore more generally angled (laterally, further away from vertical).
This greater angle applies a larger portion of the gravitational or vertical load as valgus torque (rotational force against the knee).
This, combined with the female's weaker tendons and ligaments and a narrower intercondylar notch, causes increased susceptibility to injury of the ACL in female athletes.
The pelvis of the human male is slightly narrower.
One hypothesis is that this makes it more optimized for walking and that the wider female pelvis is an evolutionary compromise between efficient walking and the need for successful childbirth.
This is termed the ''
obstetrical dilemma The obstetrical dilemma is a hypothesis to explain why humans often require assistance from other humans during childbirth to avoid complications, whereas most non-human primates give birth unassisted with relatively little difficulty. This occurs ...
''.
Disagreement exists as to the strength of the hypothesis.
Males and females do not differ in their number of ribs; both normally have twelve pairs.
The following further generalizations have been made regarding male-female skeletal differences:
* Males in general have denser, stronger
bone
A bone is a Stiffness, rigid Organ (biology), organ that constitutes part of the skeleton in most vertebrate animals. Bones protect the various other organs of the body, produce red blood cell, red and white blood cells, store minerals, provid ...
s,
tendon
A tendon or sinew is a tough, high-tensile-strength band of dense fibrous connective tissue that connects muscle to bone. It is able to transmit the mechanical forces of muscle contraction to the skeletal system without sacrificing its ability ...
s, and
ligament
A ligament is the fibrous connective tissue that connects bones to other bones. It is also known as ''articular ligament'', ''articular larua'', ''fibrous ligament'', or ''true ligament''. Other ligaments in the body include the:
* Peritoneal li ...
s.
* Female
skull
The skull is a bone protective cavity for the brain. The skull is composed of four types of bone i.e., cranial bones, facial bones, ear ossicles and hyoid bone. However two parts are more prominent: the cranium and the mandible. In humans, the ...
s and head bones differ in size and shape from the male skull, with the male
mandible
In anatomy, the mandible, lower jaw or jawbone is the largest, strongest and lowest bone in the human facial skeleton. It forms the lower jaw and holds the lower tooth, teeth in place. The mandible sits beneath the maxilla. It is the only movabl ...
generally wider, larger, and squarer than the female.
In addition, males generally have a more prominent
brow, an orbital with rounded border, and more greatly projecting
mastoid process
The mastoid part of the temporal bone is the posterior (back) part of the temporal bone, one of the bones of the skull. Its rough surface gives attachment to various muscles (via tendons) and it has openings for blood vessels. From its borders, t ...
es.
* Males have a more pronounced
Adam's apple
The Adam's apple or laryngeal prominence is the protrusion in the human neck formed by the angle of the thyroid cartilage surrounding the larynx, typically visible in men, less frequently in women.
Structure
The topographic structure which is e ...
or thyroid cartilage and deeper voices due to larger vocal cords.
* Males have larger teeth than females and a greater proportion of the tooth in males is made up of dentine, whereas females have proportionately more enamel.
Muscle mass and strength
Pubertal changes in males lead to a ten times increase in testosterone. Because of this and because males go through puberty for longer, females typically have lower total
muscle mass
Skeletal muscles (commonly referred to as muscles) are organs of the vertebrate muscular system and typically are attached by tendons to bones of a skeleton. The muscle cells of skeletal muscles are much longer than in the other types of muscle ...
than males, and also have lower muscle mass in comparison to total body mass.
Males convert more of their caloric intake into muscle and expendable circulating energy reserves, while females tend to convert more into fat deposits. As a consequence, men are generally
physically stronger than women.
Research suggests that, while men have greater total muscle areas than women, the number of muscle fibers in men and women are alike. Instead of muscle fiber composition as the main reason for men's greater absolute strength, the data indicates that it is total muscle area that is responsible for this difference.
Men's individual muscle fibers are larger than women's, which results in their more muscular appearance. Their larger muscle fibers appear responsible for their more considerable absolute force production.
The sex difference in muscle mass remains after adjusting for body weight and height.
Men are at least one-third stronger than women when adjusting for differences in total body mass, due to the higher male muscle-mass to body-mass ratio.
The greater muscle mass is reported to be due to a greater capacity for
muscular hypertrophy as a result of higher levels of circulating testosterone in males.
Gross measures of body strength suggest that women are approximately 50-60% as strong as men in the upper body, and 60-70% as strong in the lower body. One study of muscle strength in the
elbows
The elbow is the region between the arm and the forearm that surrounds the elbow joint. The elbow includes prominent landmarks such as the olecranon, the cubital fossa (also called the chelidon, or the elbow pit), and the lateral and the media ...
and
knees
In humans and other primates, the knee joins the thigh with the leg and consists of two joints: one between the femur and tibia (tibiofemoral joint), and one between the femur and patella (patellofemoral joint). It is the largest joint in the hu ...
—in 45 and older males and females—found the strength of females to range from 42 to 63% of male strength. Men have greater hand grip strength than women.
Differences in width of arm, thighs and calves appear during puberty.
Respiratory system
Males typically have larger
tracheae and main
bronchi
A bronchus is a passage or airway in the lower respiratory tract that conducts air into the lungs. The first or primary bronchi pronounced (BRAN-KAI) to branch from the trachea at the carina are the right main bronchus and the left main bronchus. ...
and greater
lung volume
Lung volumes and lung capacities refer to the volume of air in the lungs at different phases of the respiratory cycle.
The average total lung capacity of an adult human male is about 6 litres of air.
Tidal breathing is normal, resting breathin ...
per
body mass
Human body weight is a person's Mass versus weight, mass or weight.
Strictly speaking, body weight is the measurement of weight without items located on the person. Practically though, body weight may be measured with clothes on, but without shoe ...
.
They also have larger
heart
The heart is a muscular organ in most animals. This organ pumps blood through the blood vessels of the circulatory system. The pumped blood carries oxygen and nutrients to the body, while carrying metabolic waste such as carbon dioxide t ...
s,
10% higher
red blood cell
Red blood cells (RBCs), also referred to as red cells, red blood corpuscles (in humans or other animals not having nucleus in red blood cells), haematids, erythroid cells or erythrocytes (from Greek ''erythros'' for "red" and ''kytos'' for "holl ...
count, and higher
haemoglobin
Hemoglobin (haemoglobin BrE) (from the Greek word αἷμα, ''haîma'' 'blood' + Latin ''globus'' 'ball, sphere' + ''-in'') (), abbreviated Hb or Hgb, is the iron-containing oxygen-transport metalloprotein present in red blood cells (erythrocyte ...
hence greater oxygen-carrying capacity.
They have higher circulating
clotting factors
Coagulation, also known as clotting, is the process by which blood changes from a liquid to a gel, forming a blood clot. It potentially results in hemostasis, the cessation of blood loss from a damaged vessel, followed by repair. The mechanism ...
(
vitamin K
Vitamin K refers to structurally similar, fat-soluble vitamers found in foods and marketed as dietary supplements. The human body requires vitamin K for post-synthesis modification of certain proteins that are required for blood coagulation ...
, pro
thrombin
Thrombin (, ''fibrinogenase'', ''thrombase'', ''thrombofort'', ''topical'', ''thrombin-C'', ''tropostasin'', ''activated blood-coagulation factor II'', ''blood-coagulation factor IIa'', ''factor IIa'', ''E thrombin'', ''beta-thrombin'', ''gamma- ...
and
platelet
Platelets, also called thrombocytes (from Greek θρόμβος, "clot" and κύτος, "cell"), are a component of blood whose function (along with the coagulation factors) is to react to bleeding from blood vessel injury by clumping, thereby ini ...
s). These differences lead to faster clotting of blood and higher peripheral pain tolerance.
Sex differences in the trachea and main bronchi are not apparent until at least age 14.
On average, girls have smaller lungs than boys at birth.
Skin and hair
Skin
Men's skin is thicker and
oilier than women's skin.
Women have more
subcutaneous fat
The subcutaneous tissue (), also called the hypodermis, hypoderm (), subcutis, superficial fascia, is the lowermost layer of the integumentary system in vertebrates. The types of cells found in the layer are fibroblasts, adipose cells, and mac ...
than men. This helps keep them warmer and enables them to survive lower temperatures than men during the cold.
As a result of greater
vasoconstriction
Vasoconstriction is the narrowing of the blood vessels resulting from contraction of the muscular wall of the vessels, in particular the large arteries and small arterioles. The process is the opposite of vasodilation, the widening of blood vessel ...
, while the surface of female skin is colder than male skin, the deep-skin temperature in women is higher than in men.
Males generally have darker skin than females.
The lighter skin in females helps their bodies synthesize more
Vitamin D
Vitamin D is a group of fat-soluble secosteroids responsible for increasing intestinal absorption of calcium, magnesium, and phosphate, and many other biological effects. In humans, the most important compounds in this group are vitamin D3 (c ...
from sunlight and absorb more
calcium
Calcium is a chemical element with the symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar to ...
, which is needed during
pregnancy
Pregnancy is the time during which one or more offspring develops ( gestates) inside a woman's uterus (womb). A multiple pregnancy involves more than one offspring, such as with twins.
Pregnancy usually occurs by sexual intercourse, but ca ...
and
lactation
Lactation describes the secretion of milk from the mammary glands and the period of time that a mother lactates to feed her young. The process naturally occurs with all sexually mature female mammals, although it may predate mammals. The proces ...
.
Hair
On average, men have more
body hair
Body hair, or androgenic hair, is the terminal hair that develops on the human body during and after puberty. It is differentiated from the head hair and less visible vellus hair, which is much finer and lighter in color. The growth of androge ...
than women. Men have relatively more of a type of hair called
terminal hair
In humans, terminal hair is a variant of hair that is thick and long such as what grows on the scalp, as compared with vellus hair, colloquially known as peach fuzz, growing elsewhere.Marks, James G; Miller, Jeffery (2006)''Lookingbill and Ma ...
, especially on the
face
The face is the front of an animal's head that features the eyes, nose and mouth, and through which animals express many of their emotions. The face is crucial for human identity, and damage such as scarring or developmental deformities may aff ...
,
chest
The thorax or chest is a part of the anatomy of humans, mammals, and other tetrapod animals located between the neck and the abdomen. In insects, crustaceans, and the extinct trilobites, the thorax is one of the three main divisions of the crea ...
,
abdomen
The abdomen (colloquially called the belly, tummy, midriff, tucky or stomach) is the part of the body between the thorax (chest) and pelvis, in humans and in other vertebrates. The abdomen is the front part of the abdominal segment of the torso. ...
and back. Women have more
vellus hair
Vellus hair is short, thin, light-colored, and barely noticeable hair that develops on most of a human’s body during childhood. Exceptions include the lips, the back of the ear, the palm of the hand, the sole of the foot, some external genital ...
, which is thinner, shorter, and lighter, and therefore less visible.
Although men grow hair faster than women,
baldness
Hair loss, also known as alopecia or baldness, refers to a loss of hair from part of the head or body. Typically at least the head is involved. The severity of hair loss can vary from a small area to the entire body. Inflammation or scarrin ...
is more prevalent in men than in women. The main cause for this is
male pattern baldness
Pattern hair loss (also known as androgenetic alopecia (AGA)) is a hair loss condition that primarily affects the top and front of the scalp. In male-pattern hair loss (MPHL), the hair loss typically presents itself as either a receding front ha ...
. Male pattern baldness is a condition where hair loss occurs in a typical pattern of a receding hairline and hair thinning on the crown. It is caused by hormones and genetic predisposition.
Color
![Woman redhead natural portrait](https://upload.wikimedia.org/wikipedia/commons/7/7a/Woman_redhead_natural_portrait.jpg)
In
lighter-complected humans, male skin is visibly redder; this is due to greater blood volume rather than
melanin
Melanin (; from el, μέλας, melas, black, dark) is a broad term for a group of natural pigments found in most organisms. Eumelanin is produced through a multistage chemical process known as melanogenesis, where the oxidation of the amino ...
. Conversely, women are lighter-skinned than men in some studied human populations.
The differences in color are mainly caused by higher levels of
melanin
Melanin (; from el, μέλας, melas, black, dark) is a broad term for a group of natural pigments found in most organisms. Eumelanin is produced through a multistage chemical process known as melanogenesis, where the oxidation of the amino ...
in the skin, hair and eyes in males.
In one study, almost twice as many females as males had red or auburn hair. A higher proportion of females were also found to have
blond
Blond (male) or blonde (female), also referred to as fair hair, is a hair color characterized by low levels of the dark pigment eumelanin. The resultant visible hue depends on various factors, but always has some yellowish color. The color can ...
hair, whereas males were more likely to have black or dark brown hair.
Another study found
green eyes, which are a result of lower melanin levels, to be much more common in women than in men, at least by a factor of two.
A different study found that while women tend to have a lower frequency of black hair, men have a higher frequency of platinum blond hair, blue eyes and lighter skin. According to this one theory the cause for this is a higher frequency of genetic recombination in women than in men, possibly due to
sex-linked
Sex linked describes the sex-specific patterns of inheritance and presentation when a gene mutation (allele) is present on a sex chromosome (allosome) rather than a non-sex chromosome ( autosome). In humans, these are termed X-linked recessive, ...
genes, and as a result women tend to show less phenotypical variation in any given population.
[Interaction between loci affecting human pigmentation in Poland](_blank)
/ref>
The human sexual dimorphism in color seems to be greater in populations that are medium in skin color than in very light or very dark-colored populations.
Sexual organs and reproductive systems
Males and females have different sex organ
A sex organ (or reproductive organ) is any part of an animal or plant that is involved in sexual reproduction. The reproductive organs together constitute the reproductive system. In animals, the testis in the male, and the ovary in the female, a ...
s. Females have two ovaries that store the eggs
Humans and human ancestors have scavenged and eaten animal eggs for millions of years. Humans in Southeast Asia had domesticated chickens and harvested their eggs for food by 1,500 BCE. The most widely consumed eggs are those of fowl, especial ...
, and a uterus
The uterus (from Latin ''uterus'', plural ''uteri'') or womb () is the organ in the reproductive system of most female mammals, including humans that accommodates the embryonic and fetal development of one or more embryos until birth. The uter ...
which is connected to a vagina
In mammals, the vagina is the elastic, muscular part of the female genital tract. In humans, it extends from the vestibule to the cervix. The outer vaginal opening is normally partly covered by a thin layer of mucosal tissue called the hymen ...
. Males have testicles
A testicle or testis (plural testes) is the male reproductive gland or gonad in all bilaterians, including humans. It is homologous to the female ovary. The functions of the testes are to produce both sperm and androgens, primarily testostero ...
that produce sperm
Sperm is the male reproductive cell, or gamete, in anisogamous forms of sexual reproduction (forms in which there is a larger, female reproductive cell and a smaller, male one). Animals produce motile sperm with a tail known as a flagellum, whi ...
. The testicles are placed in the scrotum
The scrotum or scrotal sac is an anatomical male reproductive structure located at the base of the penis that consists of a suspended dual-chambered sac of skin and smooth muscle. It is present in most terrestrial male mammals. The scrotum cont ...
behind the penis
A penis (plural ''penises'' or ''penes'' () is the primary sexual organ that male animals use to inseminate females (or hermaphrodites) during copulation. Such organs occur in many animals, both vertebrate and invertebrate, but males do n ...
. The male penis and scrotum are external extremities, whereas the female sex organs are placed "inside" the body.
Male orgasm
Orgasm (from Greek , ; "excitement, swelling") or sexual climax is the sudden discharge of accumulated sexual excitement during the sexual response cycle, resulting in rhythmic, involuntary muscular contractions in the pelvic region charac ...
(and the corresponding release of ejaculate containing sperm from the testes) is essential for reproduction, whereas female orgasm is not. The female orgasm was originally believed to have no function other than pleasure. Later evidence suggests that it evolved as a discriminatory advantage in regards to mate selection.
Female ejaculation
Female ejaculation is characterized as an expulsion of fluid from the Skene's gland at the lower end of the urethra during or before an orgasm. It is also known colloquially as squirting (or gushing), although research indicates that female eja ...
has been observed for 2,000 years. It refers to the release of fluid experienced by some females during orgasm. The components of the ejaculate are comparable to that of the male ejaculate. The release of this fluid is a product of the Skene's gland
In female human anatomy, Skene's glands or the Skene glands ( , also known as the lesser vestibular glands, paraurethral glands) are glands located around the lower end of the urethra. The glands are surrounded by tissue that swells with blood ...
(female prostate), located within the walls of the urethra. The female prostate is much smaller than the male prostate but seems to behave in a similar fashion. Female ejaculate, though, does not contain sperm. The female prostate is visible through MRI and ultrasound.
Reproductive capacity and cost
Males typically produce billions of sperm each month, many of which are capable of fertilization. Females typically produce one ovum a month that can be fertilized into an embryo. Thus during a lifetime males are able to father a significantly greater number of children than females can give birth to. The most fertile female, according to the Guinness Book of World Records, was the wife of Feodor Vassilyev of Russia (1707–1782) who had 69 surviving children. The most prolific father of all time is believed to be the last Sharifian Emperor of Morocco, Mulai Ismail (1646–1727) who reportedly fathered more than 800 children from a harem
Harem (Persian: حرمسرا ''haramsarā'', ar, حَرِيمٌ ''ḥarīm'', "a sacred inviolable place; harem; female members of the family") refers to domestic spaces that are reserved for the women of the house in a Muslim family. A hare ...
of 500 women.
Fertility
Female fertility
Fertility is the capability to produce offspring through reproduction following the onset of sexual maturity. The fertility rate is the average number of children born by a female during her lifetime and is quantified Demography, demographicall ...
declines after age 30 and ends with the menopause
Menopause, also known as the climacteric, is the time in women's lives when menstrual periods stop permanently, and they are no longer able to bear children. Menopause usually occurs between the age of 47 and 54. Medical professionals often d ...
. Female physical experiences vary depending on external forces such as diet, marriage patterns, culture, and other aspects. In Western nations menstruation begins to affect females at 13 and menopause starts around 51. In non-industrialized countries, on the other hand, most females begin menstruation at a later age. More lactation in the lifetime of non-western females inhibits ovulation and extends the number of fertile years. Pregnancy in the 40s or later has been correlated with increased risk of Down syndrome
Down syndrome or Down's syndrome, also known as trisomy 21, is a genetic disorder caused by the presence of all or part of a third copy of chromosome 21. It is usually associated with physical growth delays, mild to moderate intellectual dis ...
in children. Males are capable of fathering children into old age. Paternal age effects in children include multiple sclerosis
Multiple (cerebral) sclerosis (MS), also known as encephalomyelitis disseminata or disseminated sclerosis, is the most common demyelinating disease, in which the insulating covers of nerve cells in the brain and spinal cord are damaged. This d ...
, autism
The autism spectrum, often referred to as just autism or in the context of a professional diagnosis autism spectrum disorder (ASD) or autism spectrum condition (ASC), is a neurodevelopmental condition (or conditions) characterized by difficulti ...
, breast cancer
Breast cancer is cancer that develops from breast tissue. Signs of breast cancer may include a lump in the breast, a change in breast shape, dimpling of the skin, milk rejection, fluid coming from the nipple, a newly inverted nipple, or a re ...
and schizophrenia
Schizophrenia is a mental disorder characterized by continuous or relapsing episodes of psychosis. Major symptoms include hallucinations (typically hearing voices), delusions, and disorganized thinking. Other symptoms include social withdra ...
, as well as reduced intelligence.
Adriana Iliescu
Adriana Iliescu (born 31 May 1938) is a Romanian retired university teacher, philologist and author of children's novels. She received international media attention in 2005, when she gave birth to daughter Eliza at age 66, making her the oldest ...
was reported as the world's oldest woman to give birth
Birth is the act or process of bearing or bringing forth offspring, also referred to in technical contexts as parturition. In mammals, the process is initiated by hormones which cause the muscular walls of the uterus to contract, expelling the f ...
, at age 66. Her record stood until Maria del Carmen Bousada de Lara gave birth to twin sons at Sant Pau Hospital in Barcelona, Spain on December 29, 2006, at the age of 67. In both cases IVF
In vitro fertilisation (IVF) is a process of fertilisation where an egg is combined with sperm in vitro ("in glass"). The process involves monitoring and stimulating an individual's ovulatory process, removing an ovum or ova (egg or eggs) f ...
was used. The oldest known father was former Australian miner Les Colley, who fathered a child at age 93.
Brain and nervous system
Brain
The brains of humans, like many animals, are slightly different for male
Male (symbol: ♂) is the sex of an organism that produces the gamete (sex cell) known as sperm, which fuses with the larger female gamete, or ovum, in the process of fertilization.
A male organism cannot reproduce sexually without access to ...
s and female
Female (Venus symbol, symbol: ♀) is the sex of an organism that produces the large non-motile ovum, ova (egg cells), the type of gamete (sex cell) that fuses with the Sperm, male gamete during sexual reproduction.
A female has larger gamet ...
s.
Brain size
Early research into the differences between male and female brains showed that male brains are, on average, larger than female brains. This research was frequently cited to support the assertion that women are less intelligent than men. One of the most influential early researchers on this topic was Paul Broca
Pierre Paul Broca (, also , , ; 28 June 1824 – 9 July 1880) was a French physician, anatomist and anthropologist. He is best known for his research on Broca's area, a region of the frontal lobe that is named after him. Broca's area is involve ...
. In 1861, he examined 432 human brains from cadavers and found that the brains of men had an average weight of 1325 grams, while the brains of women had an average weight of 1144 grams. This study, however, did not control for differences in body size or age. Later studies have shown that while men's brains are an average of 10-15% larger and heavier than women's brains, there is relatively no difference when controlling for body weight. This means the brain-to-body mass ratio is, on average, approximately the same for both sexes. Comparing a man and a woman of the same body size, an average difference of 100 grams in brain-mass is present, the man having the bigger and heavier brain. This difference of 100 grams applies over the whole range of human sizes.
Brain structure
Structural brain differences usually correspond to sexually dimorphic attributes that bring about functional brain differences.
On average, female brains have a larger ratio of grey matter to the white matter than males (particularly in the dorsolateral prefrontal cortex and superior temporal gyrus), even when sex-differences in the total intracranial volume are taken into consideration. Most notably, males have a larger amount of white matter in the frontal and temporal perisylvian region, and in the temporal stem and optic radiation, of the left hemisphere, whereas females have a larger amount of gray matter in the superior temporal gyrus
The superior temporal gyrus (STG) is one of three (sometimes two) gyri in the temporal lobe of the human brain, which is located laterally to the head, situated somewhat above the external ear.
The superior temporal gyrus is bounded by:
* the lat ...
, planum temporale
The planum temporale is the cortical area just posterior to the auditory cortex (Heschl's gyrus) within the Sylvian fissure. It is a triangular region which forms the heart of Wernicke's area, one of the most important functional areas for languag ...
, Heschl gyrus, cingulate gyrus
The cingulate cortex is a part of the brain situated in the medial aspect of the cerebral cortex. The cingulate cortex includes the entire cingulate gyrus, which lies immediately above the corpus callosum, and the continuation of this in the ci ...
, inferior frontal, and central sulci margins, of the left hemisphere.
The degree of hemispheric asymmetry in males corresponds to the relative size of corpus callosum
The corpus callosum (Latin for "tough body"), also callosal commissure, is a wide, thick nerve tract, consisting of a flat bundle of commissural fibers, beneath the cerebral cortex in the brain. The corpus callosum is only found in placental mam ...
; however, this is not true in females. An increase in hemispheric asymmetry in male brains causes a male sex-dependent decrease in inter-hemispheric connectivity. Many studies suggest that, on average, female brains have more commissural tracts involved in inter-hemispheric connectivity than males. Specifically, studies suggests that:
* The anterior commissure
The anterior commissure (also known as the precommissure) is a white matter tract (a bundle of axons) connecting the two temporal lobes of the cerebral hemispheres across the midline, and placed in front of the columns of the fornix. In most exist ...
is larger in females than males.
* The massa intermedia is more abundant in females than males.
* Females have a larger ratio of the cross-sectional area of the corpus callosum to cerebral volume and to forebrain size than males.
A few studies have reached contrary conclusions.
Typically, male brains are more asymmetric than female brains. Females have less asymmetry than males between left and right hemispheric cortical thickness. Males have a larger intra-hemispheric long-range interconnectivity than females, whereas females have larger inter-hemispheric connectivity. Males have larger left-hemispheric asymmetries than females in a number of brain areas, including the superior temporal gyrus, Heschl gyrus, deeper central sulcus, overall temporal and parietal, and inferior parietal lobule
The inferior parietal lobule (subparietal district) lies below the horizontal portion of the intraparietal sulcus, and behind the lower part of the postcentral sulcus. Also known as Geschwind's territory after Norman Geschwind, an American neurolo ...
, thalamus
The thalamus (from Greek θάλαμος, "chamber") is a large mass of gray matter located in the dorsal part of the diencephalon (a division of the forebrain). Nerve fibers project out of the thalamus to the cerebral cortex in all directions, ...
and posterior cingulate
The posterior cingulate cortex (PCC) is the caudal part of the cingulate cortex, located posterior to the anterior cingulate cortex. This is the upper part of the "limbic lobe". The cingulate cortex is made up of an area around the midline of the ...
. A few studies seemed to indicate otherwise.
There are also differences in the structure of specific areas of the brain. On average, the SDN has been repeatedly found to be considerably larger in males than in females. The volume of the SDN was 2.2 times as large in males as in females. On average, the BSTc is twice as large in men as in women. On average, the INAH-3 is significantly larger in males than in females regardless of age. Two studies found that men have larger parietal lobe
The parietal lobe is one of the four major lobes of the cerebral cortex in the brain of mammals. The parietal lobe is positioned above the temporal lobe and behind the frontal lobe and central sulcus.
The parietal lobe integrates sensory informa ...
s, an area responsible for sensory input including spatial sense and navigation; though, another study failed to find any statistically significant difference. At the same time, females have larger Wernicke's and Broca's area
Broca's area, or the Broca area (, also , ), is a region in the frontal lobe of the dominant Cerebral hemisphere, hemisphere, usually the left, of the Human brain, brain with functions linked to speech production.
Language processing in the brai ...
s, areas responsible for language processing. Studies using MRI
Magnetic resonance imaging (MRI) is a medical imaging technique used in radiology to form pictures of the anatomy and the physiological processes of the body. MRI scanners use strong magnetic fields, magnetic field gradients, and radio waves ...
scanning have shown that the auditory and language-related regions in the left hemisphere are proportionally expanded in females versus in males. Conversely, the primary visual, and visuo-spatial association areas of the parietal lobes are proportionally larger in males. The corpus callous is located at the sagittal divide and is the primary commissure
A commissure () is the location at which two objects abut or are joined. The term is used especially in the fields of anatomy and biology.
* The most common usage of the term refers to the brain's commissures, of which there are five. Such a commi ...
in the human brain. It connects the left and right hemispheres of the cerebral cortex, which allows them to communicate with each other. With respect to language, males predominantly use their left hemisphere but females use both their right and left hemispheres. The right hemisphere controls emotion, so using the right hemisphere adds more prosody to speech. In males, the corpus callosum is larger than females. However, the splenium and the isthmus subregions of the corpus callosum are larger in females. The genu subregion is larger in males. These subregions may serve as the basis for sex differences in language. However, a 1997 meta-study concluded that there is no relative size difference, and that the larger corpus callosum in males is due to generally larger brains in males on average.
In total and on average, females have a higher percentage of grey matter
Grey matter is a major component of the central nervous system, consisting of neuronal cell bodies, neuropil (dendrites and unmyelinated axons), glial cells (astrocytes and oligodendrocytes), synapses, and capillaries. Grey matter is distingui ...
in comparison to males, and males a higher percentage of white matter
White matter refers to areas of the central nervous system (CNS) that are mainly made up of myelinated axons, also called tracts. Long thought to be passive tissue, white matter affects learning and brain functions, modulating the distribution ...
. However, some researchers maintain that as males have larger brains on average than females, when adjusted for total brain volume, the grey matter differences between sexes is small or nonexistent. Thus, the percentage of grey matter appears to be more related to brain size than it is to gender.
In 2005, Haier ''et al.'' reported that, compared with men, women show fewer grey matter areas associated with intelligence, but more white matter areas associated with intelligence. He concluded that "men and women apparently achieve similar IQ results with different brain regions, suggesting that there is no singular underlying neuroanatomical structure to general intelligence and that different types of brain designs may manifest equivalent intellectual performance."[
*] Using brain mapping
Brain mapping is a set of neuroscience techniques predicated on the mapping of (biological) quantities or properties onto spatial representations of the (human or non-human) brain resulting in maps.
According to the definition established in ...
, it was shown that men have more than six times the amount of gray matter related to general intelligence than women, and women have nearly ten times the amount of white matter related to intelligence than men. They also report that the brain areas correlated with IQ differ between the sexes. In short, men and women apparently achieve similar IQ results with different brain regions. Other differences that have been established include greater length in males of myelinated axons in their white matter (176,000 km compared to 146,000 km); and 33% more synapses per mm3 of cerebral cortex. Another difference is that females generally have faster blood flow to their brains and lose less brain tissue as they age than males do. Additionally, depression and chronic anxiety are much more common in women than in men, and it has been speculated by some that this is due to differences in the brain's serotonin
Serotonin () or 5-hydroxytryptamine (5-HT) is a monoamine neurotransmitter. Its biological function is complex and multifaceted, modulating mood, cognition, reward, learning, memory, and numerous physiological processes such as vomiting and vas ...
system. Others contend this speculation ignores the social and material differences between men and women that are known to impact anxiety and depression.
The amygdala, which is the structure that responds to emotionally arousing information, respond to the environment, and reacts with stress. The male amygdala is proportionally larger than that in women, causing sex to be a determining factor in reactions to stress. In studies of rats, there are more numerous interconnections seen in males in regard to this structure, suggesting the same pattern in humans. Katharina Braun and company (Otto von Guericke University, Magdeburg, Germany) studied a litter of Degu puppies removed from their mother and determined that hearing their mother's call produced a higher concentration of serotonin in males' amygdala and a decreased concentration in females' amygdala. In this case, stress causes females' emotion regulation to drop, while males seem to keep more of an even keel. While this study was limited to rodents, it provides a possible explanation of why anxiety disorders occur more often among human females than males.[; ] Also, the hypothalamus and front medial area, both of which are associated with emotional processing, are larger in males than females. Other brain areas related to emotion, such as the orbitofrontal cortex, medial paralimbic region, and hippocampus are larger in females than males.
The hippocampus has been proven by imaging to be larger in women than men. The hippocampus is crucial for memory storage and spatial mapping of the physical environment. This structural difference may be responsible for variations in behavior between the sexes. Studies show that women are more likely to navigate using landmarks, while men are more likely to estimate distance in space or orientation. Studies of rats show that males could learn better in the face of acute stress, while chronic stress is dealt with better by females. Sex hormones may influence female hippocampal cells to tolerate brain damage better than the same cells in men. The studies of the rats' influx and deflation of hippocampal cells can be translated to the difference in memory and spatial behaviors between the sexes.
On average, Onuf's nucleus
Onuf's nucleus is a distinct group of neurons located in the ventral part ( laminae IX) of the anterior horn of the sacral region of the human spinal cord involved in the maintenance of micturition and defecatory continence, as well as muscular ...
is sexually dimorphic, meaning that there are differences in Onuf's nucleus between males and females of the same species. Males of these species have more of these motoneurons than do their female counterparts.
= Brain connectivity
=
Research done at the Medical School of University of Pennsylvania
The University of Pennsylvania (also known as Penn or UPenn) is a private research university in Philadelphia. It is the fourth-oldest institution of higher education in the United States and is ranked among the highest-regarded universitie ...
found substantial differences in brain connectivity between males and females in 2013. The study examined 949 individuals (521 females and 428 males) of ages between 8 and 22. Overall, male brains showed more connectivity from back to front and within hemisphere
Hemisphere refers to:
* A half of a sphere
As half of the Earth
* A hemisphere of Earth
** Northern Hemisphere
** Southern Hemisphere
** Eastern Hemisphere
** Western Hemisphere
** Land and water hemispheres
* A half of the (geocentric) celes ...
s, while female brains showed more connectivity between the left and right hemispheres of the cerebrum. In contrast to connectivity to the cerebrum
The cerebrum, telencephalon or endbrain is the largest part of the brain containing the cerebral cortex (of the two cerebral hemispheres), as well as several subcortical structures, including the hippocampus, basal ganglia, and olfactory bulb. In ...
, in the cerebellum
The cerebellum (Latin for "little brain") is a major feature of the hindbrain of all vertebrates. Although usually smaller than the cerebrum, in some animals such as the mormyrid fishes it may be as large as or even larger. In humans, the cerebel ...
, the part of the brain that plays a major role in the motor tasks, females showed higher intra-hemispheric connectivity while males showed higher inter-hemispheric connectivity. The differences were more pronounced in people aged 14 or older.
The researchers stated that these findings potentially provide a neural basis for observable sex differences in psychology. The research was consistent with previous studies that found that females performed better than males on tasks of attention, face and word memory, and social cognition tests, while males performed better on spatial processing and sensorimotor skill tasks. On average, men outperformed women at learning and accomplishing single tasks, like cycling and navigating directions, while females had better memory and social cognition skills making them more adjusted to multitasking and coming up with consensus solutions. It has been suggested that the increased differentiation of brain connectivity in adolescence is in correlation with hormonal changes in puberty
Puberty is the process of physical changes through which a child's body matures into an adult body capable of sexual reproduction. It is initiated by hormonal signals from the brain to the gonads: the ovaries in a girl, the testes in a boy. ...
.
A 2014 study by the same research group using rsfc-MRI (resting-state functional connectivity MRI) found similar results to the previous one, with males on average outperforming females on motor
An engine or motor is a machine designed to convert one or more forms of energy into mechanical energy.
Available energy sources include potential energy (e.g. energy of the Earth's gravitational field as exploited in hydroelectric power gen ...
and spatial cognitive tests, and females on average outperforming males on emotional recognition and nonverbal reasoning tasks.
Genetic and hormonal causes
Both genes
In biology, the word gene (from , ; "...Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation'' or ''birth'' or ''gender'') can have several different meanings. The Mendelian gene is a ba ...
and hormone
A hormone (from the Greek participle , "setting in motion") is a class of signaling molecules in multicellular organisms that are sent to distant organs by complex biological processes to regulate physiology and behavior. Hormones are required ...
s affect the formation of human brains before birth
Birth is the act or process of bearing or bringing forth offspring, also referred to in technical contexts as parturition. In mammals, the process is initiated by hormones which cause the muscular walls of the uterus to contract, expelling the f ...
, as well as the behavior of adult individuals. Several genes that code for differences between male and female brains have been identified. In the human brain
The human brain is the central organ of the human nervous system, and with the spinal cord makes up the central nervous system. The brain consists of the cerebrum, the brainstem and the cerebellum. It controls most of the activities of the ...
, a difference between sexes was observed in the transcription
Transcription refers to the process of converting sounds (voice, music etc.) into letters or musical notes, or producing a copy of something in another medium, including:
Genetics
* Transcription (biology), the copying of DNA into RNA, the fir ...
of the PCDH11X
Protocadherin 11 X-linked, also known as PCDH11X, is a protein which in humans is encoded by the ''PCDH11X'' gene.
Function
This gene belongs to the protocadherin gene family, a subfamily of the cadherin superfamily. The encoded protein consis ...
/Y gene pair, a pair unique to ''Homo sapiens
Humans (''Homo sapiens'') are the most abundant and widespread species of primate, characterized by bipedalism and exceptional cognitive skills due to a large and complex brain. This has enabled the development of advanced tools, culture, ...
''. It has been argued that the Y chromosome is primarily responsible for males being more susceptible to mental illnesses. Several psychological studies contradict this however, as it has been found that female patients are actually more than twice as likely as male patients to be susceptible to depressive episodes and generalized anxiety, and additionally that progesterone levels in females actually stall the body's ability to turn off stressor hormones resulting in female subjects entering depressive episodes at even lower levels of stress than male subjects.
Hormones significantly affect human brain formation, as well as brain development at puberty. A 2004 review in ''Nature Reviews Neuroscience
''Nature Reviews Neuroscience'' is a monthly peer-reviewed review journal published by Nature Portfolio. It was established in 2000. The editor-in-chief is Darran Yates.
Abstracting and indexing
The journal is abstracted and indexed in:
*PubMed/ ...
'' observed that "because it is easier to manipulate hormone levels than the expression of sex chromosome genes, the effects of hormones have been studied much more extensively, and are much better understood, than the direct actions in the brain of sex chromosome genes." It concluded that while "the differentiating effects of gonadal secretions seem to be
dominant," the existing body of research "supports the idea that sex differences in neural expression
of X and Y genes significantly contribute to sex differences in brain functions and disease."
Selective pressures of evolution can cause innate biological brain differences before a child is even born. Research done on vervet monkeys showed that male and female monkeys gravitated towards sex-typical preferred toys. This study controls for external societal influence by using monkeys as the subject and projects results to humans, the closest animal relative. A separate study was done on one-day-old infants to see if infants diverted attention differently between the sexes. Results showed that there must be some innate mechanism that differs between the sexes. This innate mechanism is evolutionary in the sense that the hormones for females are concurrently passed down to other females, and the same with males.
Other than external genitals, there are few physical differences before puberty. Small differences in height and start of physical maturity are seen. In the first decade of human life, there is a significant amount of overlap between children of both sexes. The gradual growth in sex difference throughout a person's life is a product of various hormones. Testosterone
Testosterone is the primary sex hormone and anabolic steroid in males. In humans, testosterone plays a key role in the development of Male reproductive system, male reproductive tissues such as testes and prostate, as well as promoting secondar ...
is the major active hormone in male development while estrogen
Estrogen or oestrogen is a category of sex hormone responsible for the development and regulation of the female reproductive system and secondary sex characteristics. There are three major endogenous estrogens that have estrogenic hormonal acti ...
is the dominant female hormone. These hormones are not, however, limited to each sex. Both males and females have both testosterone and estrogen.
Sensory systems
* Some studies have shown that females have a more sensitive sense of smell than males, both in the differentiation of odors and in the detection of slight or faint odors.
* Females have more pain receptors in the skin. That may contribute to the lower pain tolerance of women. While most women expect to be less tolerant to pain, men expect to be more tolerant and therefore report agitation later. Due to variation across societies of gender roles, results of pain studies also vary depending on gender expectations.
* Females also report a higher prevalence of many pain-related diseases and syndromes, particularly auto-immune diseases. In a 2005 study, Holdcroft and Beckley show a higher female prevalence of many conditions of the head and neck (e.g., migraine
Migraine (, ) is a common neurological disorder characterized by recurrent headaches. Typically, the associated headache affects one side of the head, is pulsating in nature, may be moderate to severe in intensity, and could last from a few hou ...
), limbs (e.g., carpal tunnel syndrome
Carpal tunnel syndrome (CTS) is the collection of symptoms and signs associated with median neuropathy at the carpal tunnel. Most CTS is related to idiopathic compression of the median nerve as it travels through the wrist at the carpal tunn ...
), internal organs (IBS), and more general conditions (multiple sclerosis
Multiple (cerebral) sclerosis (MS), also known as encephalomyelitis disseminata or disseminated sclerosis, is the most common demyelinating disease, in which the insulating covers of nerve cells in the brain and spinal cord are damaged. This d ...
). Fewer conditions show a male prevalence: e.g., cluster headache, gout.
* In addition to defined diseases and syndromes, many common "everyday" pains appear to overburden women rather than men. Therefore, studies consistently find that women report more severe pain, more frequent pain, longer-lasting pain, and wider-ranging pain than men. For example, common painful conditions such as dysmenorrhea
Dysmenorrhea, also known as period pain, painful periods or menstrual cramps, is pain during menstruation. Its usual onset occurs around the time that menstruation begins. Symptoms typically last less than three days. The pain is usually in the ...
may predispose females to more widespread musculoskeletal pains.
*Women show higher performance levels on tests of verbal fluency. This may be because the female auditory cortex is denser than that of the male. This difference and other sensory differences like it could be because of the sex hormones that impact the fetal brain during development.
Immune system
Strength and type of immune response differ in men and women. Generally speaking, women have a stronger immune response than men. This results in men having a higher morbidity and mortality from infectious diseases than women do, and lower rates of auto-immune diseases.
Tissues and hormones
* Women generally have a higher body fat percentage
The body fat percentage (BFP) of a human or other living being is the total mass of fat divided by total body mass, multiplied by 100; body fat includes essential body fat and storage body fat. Essential body fat is necessary to maintain life and ...
than men, whereas men generally have more muscle tissue mass.
* Women usually have lower blood pressure than men, and women's hearts beat faster, even when they are asleep.
* Men and women have different levels of certain hormone
A hormone (from the Greek participle , "setting in motion") is a class of signaling molecules in multicellular organisms that are sent to distant organs by complex biological processes to regulate physiology and behavior. Hormones are required ...
s. Men have a higher concentration of androgen
An androgen (from Greek ''andr-'', the stem of the word meaning "man") is any natural or synthetic steroid hormone that regulates the development and maintenance of male characteristics in vertebrates by binding to androgen receptors. This inc ...
s while women have a higher concentration of estrogen
Estrogen or oestrogen is a category of sex hormone responsible for the development and regulation of the female reproductive system and secondary sex characteristics. There are three major endogenous estrogens that have estrogenic hormonal acti ...
s.
*To date, wound healing studies have chiefly reported a female advantage in healing of dermal wounds. On the other hand, studies have found a male advantage in healing rates of mucosal wounds. Thus, gender advantages in wound healing appear to be tissue specific.
* Adult men have approximately 5.2 million red blood cells per cubic millimeter of blood, whereas women have approximately 4.6 million.
* Females typically have more white blood cell
White blood cells, also called leukocytes or leucocytes, are the cell (biology), cells of the immune system that are involved in protecting the body against both infectious disease and foreign invaders. All white blood cells are produced and de ...
s (stored and circulating), more granulocyte
Granulocytes are
cells in the innate immune system characterized by the presence of specific granules in their cytoplasm. Such granules distinguish them from the various agranulocytes. All myeloblastic granulocytes are polymorphonuclear. They ha ...
s, and B and T lymphocyte
A lymphocyte is a type of white blood cell (leukocyte) in the immune system of most vertebrates. Lymphocytes include natural killer cells (which function in cell-mediated, cytotoxic innate immunity), T cells (for cell-mediated, cytotoxic ad ...
s. Additionally, they produce more antibodies
An antibody (Ab), also known as an immunoglobulin (Ig), is a large, Y-shaped protein used by the immune system to identify and neutralize foreign objects such as pathogenic bacteria and viruses. The antibody recognizes a unique molecule of the ...
at a faster rate than males. Hence they develop fewer infectious
An infection is the invasion of tissues by pathogens, their multiplication, and the reaction of host tissues to the infectious agent and the toxins they produce. An infectious disease, also known as a transmissible disease or communicable dise ...
diseases and succumb for shorter periods.
* Recent findings revealed that there are several differences in cellular characteristics (e.g., cytoskeleton) of female and male cells.
Health
Life span
Females live longer than males in most countries around the world. In Russia, however, the sex-associated gap has been increasing as male life expectancy declines.
The longer average life span of women can lead to skewed statistical results in regard to sex differences. For example, women are often seen to be at a higher risk of bone fracture due to osteoporosis. Although women do lose bone density faster than men after menopause, the data shows a larger disparity because there are more older women in the population.
Illness and injury
Sex chromosome disorders
Certain diseases and conditions are clearly sex-related in that they are caused by the same chromosome
A chromosome is a long DNA molecule with part or all of the genetic material of an organism. In most chromosomes the very long thin DNA fibers are coated with packaging proteins; in eukaryotic cells the most important of these proteins are ...
s that regulate sex differentiation. Some conditions are X-linked recessive
X-linked recessive inheritance is a mode of inheritance in which a mutation in a gene on the X chromosome causes the phenotype to be always expressed in males (who are necessarily homozygous for the gene mutation because they have one X and one Y ...
, in that the gene is carried on the X chromosome. Genetic females (XX) will show symptoms of the disease only if both their X chromosomes are defective with a similar deficiency, whereas genetic males (XY) will show symptoms of the disease if their only X chromosome is defective. (A woman may carry such a disease on one X chromosome but not show symptoms if the other X chromosome works sufficiently.) For this reason, such conditions are far more common in males than in females.
X-linked recessive disorders include:
*Red-green colour blindness
*Haemophilia A (factor VIII)
*Haemophilia B (factor IX)
*Duchenne Muscular Dystrophy
*X-linked agammaglobulinaemia
*X-linked ichythyosis
*Becker muscular dystrophy
*Non-specific X-linked mental retardation
X-linked dominant disorders include:
*Xg blood group
*Vitamin D resistant rickets
*Rett's syndrome
*Fragile X syndrome
Fragile X syndrome (FXS) is a genetic disorder characterized by mild-to-moderate intellectual disability. The average IQ in males with FXS is under 55, while about two thirds of affected females are intellectually disabled. Physical features may ...
There are diseases that are caused by a defective Y chromosome or a defective number of them.
Differences not linked to sex chromosomes
The World Health Organization
The World Health Organization (WHO) is a specialized agency of the United Nations responsible for international public health. The WHO Constitution states its main objective as "the attainment by all peoples of the highest possible level of h ...
(WHO) has produced a number of reports on gender and health. The following trends are shown:
* Overall rates of mental illness are similar for men and women. There is no significant gender difference in rates of schizophrenia
Schizophrenia is a mental disorder characterized by continuous or relapsing episodes of psychosis. Major symptoms include hallucinations (typically hearing voices), delusions, and disorganized thinking. Other symptoms include social withdra ...
and bipolar depression
Bipolar disorder, previously known as manic depression, is a mental disorder characterized by periods of depression and periods of abnormally elevated mood that last from days to weeks each. If the elevated mood is severe or associated with ...
. Women are more likely to suffer from unipolar depression
Major depressive disorder (MDD), also known as clinical depression, is a mental disorder characterized by at least two weeks of pervasive low mood, low self-esteem, and loss of interest or pleasure in normally enjoyable activities. Introdu ...
, anxiety
Anxiety is an emotion which is characterized by an unpleasant state of inner turmoil and includes feelings of dread over anticipated events. Anxiety is different than fear in that the former is defined as the anticipation of a future threat wh ...
, eating disorders
An eating disorder is a mental disorder defined by abnormal eating behaviors that negatively affect a person's physical or mental health. Only one eating disorder can be diagnosed at a given time. Types of eating disorders include binge eating ...
, and post-traumatic stress disorder
Post-traumatic stress disorder (PTSD) is a mental and behavioral disorder that can develop because of exposure to a traumatic event, such as sexual assault, warfare, traffic collisions, child abuse, domestic violence, or other threats on ...
. Men are more likely to suffer from alcoholism
Alcoholism is, broadly, any drinking of alcohol (drug), alcohol that results in significant Mental health, mental or physical health problems. Because there is disagreement on the definition of the word ''alcoholism'', it is not a recognize ...
and antisocial personality disorder
Antisocial personality disorder (ASPD or infrequently APD) is a personality disorder characterized by a long-term pattern of disregard of, or violation of, the rights of others as well as a difficulty sustaining long-term relationships. Lack ...
, as well as developmental psychiatric disorders such as autism spectrum disorder
The autism spectrum, often referred to as just autism or in the context of a professional diagnosis autism spectrum disorder (ASD) or autism spectrum condition (ASC), is a neurodevelopmental disorder, neurodevelopmental condition (or conditions) ...
s and Tourette syndrome
Tourette syndrome or Tourette's syndrome (abbreviated as TS or Tourette's) is a common neurodevelopmental disorder that begins in childhood or adolescence. It is characterized by multiple movement (motor) tics and at least one vocal (phonic) ...
.
* Women are more likely to suffer from depression, due in part to the low social status being such a powerful predictor for depression.
* While men are more likely to suffer from alcoholism, women are more prone to addiction. This is because estrogen boosts the release of dopamine in brain regions important for regulating drug-seeking behavior, making women more vulnerable to dependence.
* Schizophrenia does not show prevalence differences of significance among sexes, but there is a difference in the brain structures related. Women naturally have a higher orbitofrontal-to-amygdala ratio (OAR) than men, but not schizophrenic women (lower OAR). Men with schizophrenia however, have a higher orbitofrontal-to-amygdala ratio than that of healthy men.
* Before menopause
Menopause, also known as the climacteric, is the time in women's lives when menstrual periods stop permanently, and they are no longer able to bear children. Menopause usually occurs between the age of 47 and 54. Medical professionals often d ...
, women are less likely to suffer from cardiovascular disease
Cardiovascular disease (CVD) is a class of diseases that involve the heart or blood vessels. CVD includes coronary artery diseases (CAD) such as angina and myocardial infarction (commonly known as a heart attack). Other CVDs include stroke, h ...
. However, after age 60, the risk for both men and women is the same.
* Overall, men are more likely to suffer from cancer
Cancer is a group of diseases involving abnormal cell growth with the potential to invade or spread to other parts of the body. These contrast with benign tumors, which do not spread. Possible signs and symptoms include a lump, abnormal b ...
, with much of this driven by lung cancer
Lung cancer, also known as lung carcinoma (since about 98–99% of all lung cancers are carcinomas), is a malignant lung tumor characterized by uncontrolled cell growth in tissue (biology), tissues of the lung. Lung carcinomas derive from tran ...
. In most countries, more men than women smoke
Smoke is a suspension of airborne particulates and gases emitted when a material undergoes combustion or pyrolysis, together with the quantity of air that is entrained or otherwise mixed into the mass. It is commonly an unwanted by-product ...
, although this gap is narrowing especially among young women.
* Women are twice as likely to be blind as men. In developed countries, this may be linked to higher life expectancy and age-related conditions. In developing countries, women are less likely to get timely treatments for conditions that lead to blindness such as cataracts and trachoma
Trachoma is an infectious disease caused by bacterium ''Chlamydia trachomatis''. The infection causes a roughening of the inner surface of the eyelids. This roughening can lead to pain in the eyes, breakdown of the outer surface or cornea of ...
.
* Women are more likely to suffer from osteoarthritis
Osteoarthritis (OA) is a type of degenerative joint disease that results from breakdown of joint cartilage and underlying bone which affects 1 in 7 adults in the United States. It is believed to be the fourth leading cause of disability in the w ...
and osteoporosis
Osteoporosis is a systemic skeletal disorder characterized by low bone mass, micro-architectural deterioration of bone tissue leading to bone fragility, and consequent increase in fracture risk. It is the most common reason for a broken bone ...
. The density of bones depends upon the stresses that are put on them through exercise. Exercise and activity in childhood help to build up higher density bones. Although in Britain women's bones are less dense even before menopause, in some African societies, men and women are equally susceptible to osteoporosis.
Infectious disease prevalence varies - this is largely due to cultural and exposure factors. In particular the WHO notes that:
* Worldwide, more men than women are infected with HIV
The human immunodeficiency viruses (HIV) are two species of ''Lentivirus'' (a subgroup of retrovirus) that infect humans. Over time, they cause acquired immunodeficiency syndrome (AIDS), a condition in which progressive failure of the immune ...
. The exception is sub-Saharan Africa
Sub-Saharan Africa is, geographically, the area and regions of the continent of Africa that lies south of the Sahara. These include West Africa, East Africa, Central Africa, and Southern Africa. Geopolitically, in addition to the List of sov ...
, where more women than men are infected.
* Adult males are more likely to be diagnosed with tuberculosis
Tuberculosis (TB) is an infectious disease usually caused by '' Mycobacterium tuberculosis'' (MTB) bacteria. Tuberculosis generally affects the lungs, but it can also affect other parts of the body. Most infections show no symptoms, in ...
.
Some other sex-related health differences include:
* Anterior cruciate ligament
The anterior cruciate ligament (ACL) is one of a pair of cruciate ligaments (the other being the posterior cruciate ligament) in the human knee. The two ligaments are also called "cruciform" ligaments, as they are arranged in a crossed formation ...
injuries, especially in basketball, occur more often in women than in men.
* From conception to death, but particularly before adulthood, females are generally less vulnerable than males to developmental difficulties and chronic illnesses. This could be due to females having two x chromosomes
The X chromosome is one of the two sex-determining chromosomes (allosomes) in many organisms, including mammals (the other is the Y chromosome), and is found in both males and females. It is a part of the XY sex-determination system and XO sex-d ...
instead of just one, or in the reduced exposure to testosterone
Testosterone is the primary sex hormone and anabolic steroid in males. In humans, testosterone plays a key role in the development of Male reproductive system, male reproductive tissues such as testes and prostate, as well as promoting secondar ...
.
See also
* Sex ratio
The sex ratio (or gender ratio) is usually defined as the ratio of males to females in a population. As explained by Fisher's principle, for evolutionary reasons this is typically about 1:1 in species which reproduce sexually. Many species devia ...
* Sex differences in psychology
Sex differences in psychology are differences in the mental functions and behaviors of the sexes and are due to a complex interplay of biological, developmental, and cultural factors. Differences have been found in a variety of fields such as ment ...
* Gender-based medicine
Sex differences in medicine include sex-specific diseases or conditions which occur only in people of one sex due to underlying biological factors (for example, prostate cancer in males or uterine cancer in females); sex-related diseases, which ar ...
* Genetics of sex
* Gender differences in coping
* Sexual dimorphism
Sexual dimorphism is the condition where the sexes of the same animal and/or plant species exhibit different morphological characteristics, particularly characteristics not directly involved in reproduction. The condition occurs in most ani ...
* Sex differentiation
Sexual differentiation is the process of development of the sex differences between males and females from an undifferentiated zygote. Sex determination is often distinct from sex differentiation; sex determination is the designation for the dev ...
* Sex and intelligence
Sex differences in human intelligence have long been a topic of debate among researchers and scholars. Most psychologists now believe that there are no significant sex differences in G factor (psychometrics), general intelligence, although abili ...
* Virilization
Virilization or masculinization is the biological development of adult male characteristics in young males or females. Most of the changes of virilization are produced by androgens.
Virilization is most commonly used in three medical and biology ...
* List of homologues of the human reproductive system
This list of related male and female reproductive organs shows how the male and female reproductive organs and the development of the reproductive system are related, sharing a common developmental path. This makes them biological homologues. T ...
* Man flu
Notes
Sources
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Further reading
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Full text
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{{DEFAULTSORT:Sex Differences In Humans
Physiology
Physiology (; ) is the scientific study of functions and mechanisms in a living system. As a sub-discipline of biology, physiology focuses on how organisms, organ systems, individual organs, cells, and biomolecules carry out the chemical ...
Social inequality