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 picture info Secondary Sex Characteristics Secondary sex characteristics are features that appear during puberty in humans, and at sexual maturity in other animals. These are particularly evident in the sexually dimorphic phenotypic traits that distinguish the sexes of a species, but unlike the Sex Sex organ">sex organs, are not directly part of the reproductive system. They are believed to be the product of sexual selection for traits which display fitness, giving an individual an advantage over its rivals in courtship and aggressive interactions [...More...] Peacock The peafowl include three species of birds in the genera Pavo and Afropavo of the Phasianidae family, the pheasants and their allies. There are two Asiatic species: the blue or Indian peafowl originally of the Indian subcontinent; and the green peafowl of Southeast Asia; and one African species, the Congo peafowl, native only to the Congo Basin. Male peafowl are known for their piercing call and their extravagant plumage. The latter is especially prominent in the Asiatic species, who have an eye-spotted "tail" or "train" of covert feathers which they display as part of a courtship ritual. The term peacock is properly reserved for the male; the female is known as a peahen, and the immature offspring are sometimes called peachicks. The functions of the elaborate iridescent coloration and large "train" of peacocks have been the subject of extensive scientific debate [...More...] Sexy Son Hypothesis The sexy son hypothesis in evolutionary biology and sexual selection—proposed by Ronald Fisher in 1930—states that a female's ideal mate choice among potential mates is one whose genes will produce male offspring with the best chance of reproductive success. This also implies that a potential mate's capacity as a parental caregiver or any other direct benefits the father can offer the mother, such as nuptial gifts or good territory, are irrelevant to his value as the potential father of the female's offspring [...More...] Facial Hair Facial hair is hair grown on the face, usually on the chin, cheeks, and upper lip region. It is typically a secondary sex characteristic of human males. Men typically start developing facial hair in the later years of puberty or adolescence, between seventeen and twenty years of age, and most do not finish developing a full adult beard until their early twenties or later. This varies, as boys may first develop facial hair between fourteen and sixteen years of age, and boys as young as eleven have been known to develop facial hair. Women are also capable of developing facial hair, especially after menopause, though typically significantly less than men. Men may style their facial hair into beards, moustaches, goatees or sideburns; others completely shave their facial hair [...More...] Adam's Apple The Adam's apple, or laryngeal prominence, is a feature of the human neck, and is the lump or protrusion that is formed by the angle of the thyroid cartilage surrounding the larynx seen especially in males. Mate Choice Mate choice, also known as intersexual selection, is an evolutionary process in which selection is dependent on the attractiveness of an individual's phenotypic traits. Evolutionary change is possible because the qualities that are desired in a mate are more frequently passed on to each generation over time. For example, if female peacocks desire mates who have a colourful plumage, then this trait will increase in frequency over time as male peacocks with a colourful plumage will have more reproductive success. Mate choice is one of two components of sexual selection, the other being intrasexual selection. Ideas on sexual selection were first introduced in 1871, by Charles Darwin, then expanded on by Ronald Fisher in 1915. At present, there are five mechanisms that explain how mate choice has evolved over time [...More...] Red Deer The red deer (Cervus elaphus) is one of the largest deer species. The red deer inhabits most of Europe, the Caucasus Mountains region, Asia Minor, Iran, parts of western Asia, and central Asia. It also inhabits the Atlas Mountains region between Morocco and Tunisia in northwestern Africa, being the only species of deer to inhabit Africa. Red deer have been introduced to other areas, including Australia, New Zealand, United States, Canada, Peru, Uruguay, Chile and Argentina. In many parts of the world, the meat (venison) from red deer is used as a food source. Red deer are ruminants, characterized by a four-chambered stomach [...More...] Charles Darwin Charles Robert Darwin, ( Plumage Plumage (Latin: plūma "feather") refers both to the layer of feathers that cover a bird and the pattern, colour, and arrangement of those feathers. The pattern and colours of plumage differ between species and subspecies, and may vary with age classes. Within species there can be different colour morphs. The placement of feathers on a bird are not haphazard, but rather emerge in organized, overlapping rows and groups, and these feather tracts are known by standardized names. Most birds moult, usually before and after breeding, resulting in a breeding or nuptial plumage and a basic plumage. Many ducks and some other species such as the red junglefowl have males wearing a bright nuptial plumage while breeding and a drab eclipse plumage for some months afterwards. The painted bunting's juveniles have two inserted moults in their first autumn, each yielding plumage like an adult females [...More...] Ronald Fisher Sir Ronald Aylmer Fisher FRS (17 February 1890 – 29 July 1962), who published as R. A. Fisher, was a British statistician and geneticist. For his work in statistics, he has been described as "a genius who almost single-handedly created the foundations for modern statistical science" and "the single most important figure in 20th century statistics". In genetics, his work used mathematics to combine Mendelian genetics and natural selection; this contributed to the revival of Darwinism in the early 20th century revision of the theory of evolution known as the modern synthesis. Fisher also did experimental agricultural research, which has saved millions from starvation. From 1919 onward, he worked at the Rothamsted Experimental Station for 14 years; there, he analysed its immense data from crop experiments since the 1840s, and developed the analysis of variance (ANOVA) [...More...] picture info Biology Biology is the natural science that studies life and living organisms, including their physical structure, chemical processes, molecular interactions, physiological mechanisms, development and evolution. Despite the complexity of the science, there are certain unifying concepts that consolidate it into a single, coherent field. Biology Biology recognizes the cell as the basic unit of life, genes as the basic unit of heredity, and evolution as the engine that propels the creation and extinction of species [...More...] Handicap Principle The handicap principle is a hypothesis originally proposed in 1975 by Israeli biologist Amotz Zahavi to explain how evolution may lead to "honest" or reliable signaling between animals which have an obvious motivation to bluff or deceive each other. The handicap principle suggests that reliable signals must be costly to the signaler, costing the signaler something that could not be afforded by an individual with less of a particular trait. For example, in the case of sexual selection, the theory suggests that animals of greater biological fitness signal this status through handicapping behaviour or morphology that effectively lowers this quality. The central idea is that sexually selected traits function like conspicuous consumption, signalling the ability to afford to squander a resource [...More...] Genetic Fitness Fitness (often denoted ${\displaystyle w}$ or ω in population genetics models) is the quantitative representation of natural and sexual selection within evolutionary biology. It can be defined either with respect to a genotype or to a phenotype in a given environment. In either case, it describes individual reproductive success and is equal to the average contribution to the gene pool of the next generation that is made by individuals of the specified genotype or phenotype. The fitness of a genotype is manifested through its phenotype, which is also affected by the developmental environment. The fitness of a given phenotype can also be different in different selective environments. With asexual reproduction, it is sufficient to assign fitnesses to genotypes. With sexual reproduction, genotypes are scrambled every generation [...More...] Pubic Hair Pubic hair is terminal body hair that is found in the genital area of adolescent and adult humans. The hair is located on and around the sex organs and sometimes at the top of the inside of the thighs. In the pubic region around the pubis bone, it is known as a pubic patch. Pubic hair is found on the scrotum in the male and on the vulva in the female. Although fine vellus hair is present in the area in childhood, pubic hair is considered to be the heavier, longer and coarser hair that develops during puberty as an effect of rising levels of androgens in males and estrogens in females. Pubic hair differs from other hair on the body and is a secondary sex characteristic. Many cultures regard pubic hair as erotic, and in most cultures pubic hair is associated with the genitals, which both men and women are expected to keep covered at all times [...More...] Metabolism Metabolism (/məˈtæbəlɪzəm/, from Greek: μεταβολή metabolē, "change") is the set of life-sustaining chemical reactions in organisms. The three main purposes of metabolism are: the conversion of food to energy to run cellular processes; the conversion of food/fuel to building blocks for proteins, lipids, nucleic acids, and some carbohydrates; and the elimination of nitrogenous wastes. These enzyme-catalyzed reactions allow organisms to grow and reproduce, maintain their structures, and respond to their environments [...More...] Good Genes Hypothesis The sexy son hypothesis in evolutionary biology and sexual selection—proposed by Ronald Fisher in 1930—states that a female's ideal mate choice among potential mates is one whose genes will produce male offspring with the best chance of reproductive success. This also implies that a potential mate's capacity as a parental caregiver or any other direct benefits the father can offer the mother, such as nuptial gifts or good territory, are irrelevant to his value as the potential father of the female's offspring [...More...]