evolutionary biology Evolutionary biology is the subfield of biology that studies the evolutionary processes (natural selection, common descent, speciation) that produced the diversity of life on Earth. It is also defined as the study of the history of life fo ...

, the flying primate hypothesis is that

megabat Megabats constitute the family Pteropodidae of the order Chiroptera (bats). They are also called fruit bats, Old World fruit bats, or—especially the genera ''Acerodon'' and ''Pteropus''—flying foxes. They are the only member of the su ...

s, a subgroup of

Chiroptera Bats are mammals of the Order (biology), order Chiroptera.''cheir'', "hand" and πτερόν''pteron'', "wing". With their forelimbs adapted as wings, they are the only mammals capable of true and sustained flight. Bats are more agile in fli ...

(also known as

flying fox ''Pteropus'' (suborder Yinpterochiroptera) is a genus of megabats which are among the largest bats in the world. They are commonly known as fruit bats or flying foxes, among other colloquial names. They live in South Asia, Southeast Asia, Aust ...

es), form an evolutionary

sister group In phylogenetics, a sister group or sister taxon, also called an adelphotaxon, comprises the closest relative(s) of another given unit in an evolutionary tree. Definition The expression is most easily illustrated by a cladogram: Taxon A and t ...

primate Primates are a diverse order of mammals. They are divided into the strepsirrhines, which include the lemurs, galagos, and lorisids, and the haplorhines, which include the tarsiers and the simians (monkeys and apes, the latter including huma ...

s. The

hypothesis A hypothesis (plural hypotheses) is a proposed explanation for a phenomenon. For a hypothesis to be a scientific hypothesis, the scientific method requires that one can test it. Scientists generally base scientific hypotheses on previous obse ...

began with

Carl Linnaeus Carl Linnaeus (; 23 May 1707 – 10 January 1778), also known after his ennoblement in 1761 as Carl von Linné Blunt (2004), p. 171. (), was a Swedish botanist, zoologist, taxonomist, and physician who formalised binomial nomenclature, the ...

in 1758, and was again advanced by J.D. Smith in 1980. It was proposed in its modern form by Australian

neuroscientist A neuroscientist (or neurobiologist) is a scientist who has specialised knowledge in neuroscience, a branch of biology that deals with the physiology, biochemistry, psychology, anatomy and molecular biology of neurons, Biological neural network, n ...

Jack Pettigrew John Douglas "Jack" Pettigrew (2 October 1943''Who's Who in Australia 2013'', Crown Content, 2012. - 7 May 2019) was an Australian neuroscientist. He was Emeritus Professor of Physiology and Director of the Vision, Touch and Hearing Research ...

in 1986 after he discovered that the connections between the

retina The retina (from la, rete "net") is the innermost, light-sensitive layer of tissue of the eye of most vertebrates and some molluscs. The optics of the eye create a focused two-dimensional image of the visual world on the retina, which then ...

and the

superior colliculus In neuroanatomy, the superior colliculus () is a structure lying on the roof of the mammalian midbrain. In non-mammalian vertebrates, the homologous structure is known as the optic tectum, or optic lobe. The adjective form ''tectal'' is commonly ...

(a region of the

midbrain The midbrain or mesencephalon is the forward-most portion of the brainstem and is associated with vision, hearing, motor control, sleep and wakefulness, arousal (alertness), and temperature regulation. The name comes from the Greek ''mesos'', " ...

) in the megabat ''

Pteropus ''Pteropus'' (suborder Yinpterochiroptera) is a genus of megabats which are among the largest bats in the world. They are commonly known as fruit bats or flying foxes, among other colloquial names. They live in South Asia, Southeast Asia, Austra ...

'' were organized in the same way found in primates, and purportedly different from all other

mammal Mammals () are a group of vertebrate animals constituting the class Mammalia (), characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fur or ...

s. This was followed up by a longer study published in 1989, in which this was supported by the analysis of many other

brain A brain is an organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It is located in the head, usually close to the sensory organs for senses such as vision. It is the most complex organ in a v ...

and body characteristics. Pettigrew suggested that flying foxes,

colugo Colugos () are arboreal gliding mammals that are native to Southeast Asia. Their closest evolutionary relatives are primates. There are just two living species of colugos: the Sunda flying lemur (''Galeopterus variegatus'') and the Philippine fly ...

s, and primates were all descendants of the same group of early

arboreal Arboreal locomotion is the Animal locomotion, locomotion of animals in trees. In habitats in which trees are present, animals have evolved to move in them. Some animals may scale trees only occasionally, but others are exclusively arboreal. Th ...

mammals. The megabat flight and the colugo

gliding Gliding is a recreational activity and competitive air sport in which pilots fly unpowered aircraft known as gliders or sailplanes using naturally occurring currents of rising air in the atmosphere to remain airborne. The word ''soaring'' is al ...

could be both seen as locomotory adaptations to a life high above the ground. The flying primate hypothesis met resistance from many zoologists. Its biggest challenges were not centered on the argument that megabats and primates are evolutionarily related, which reflects earlier ideas (such as the grouping of primates,

tree shrew The treeshrews (or tree shrews or banxrings) are small mammals native to the tropical forests of South and Southeast Asia. They make up the entire order Scandentia, which split into two families: the Tupaiidae (19 species, "ordinary" treeshrews) ...

s, colugos, and

bat Bats are mammals of the order Chiroptera.''cheir'', "hand" and πτερόν''pteron'', "wing". With their forelimbs adapted as wings, they are the only mammals capable of true and sustained flight. Bats are more agile in flight than most ...

s under the same

taxonomic Taxonomy is the practice and science of categorization or classification. A taxonomy (or taxonomical classification) is a scheme of classification, especially a hierarchical classification, in which things are organized into groups or types. ...

group, the

Superorder Order ( la, ordo) is one of the eight major hierarchical taxonomic ranks in Linnaean taxonomy. It is classified between family and class. In biological classification, the order is a taxonomic rank used in the classification of organisms and ...

Archonta The Archonta are a now-abandoned group of mammals, considered a superorder in some classifications, which consists of these orders: *Primates * Plesiadapiformes (extinct primate-like archontans) * Scandentia (treeshrews) * Dermoptera (colugos) W ...

). Rather, many biologists resisted the implication that megabats and

microbat Microbats constitute the suborder Microchiroptera within the order Chiroptera (bats). Bats have long been differentiated into Megachiroptera (megabats) and Microchiroptera, based on their size, the use of echolocation by the Microchiroptera a ...

s (or echolocating bats) formed distinct branches of mammalian

evolution Evolution is change in the heritable characteristics of biological populations over successive generations. These characteristics are the expressions of genes, which are passed on from parent to offspring during reproduction. Variation ...

, with flight having evolved twice. This implication was borne out of the fact that microbats do not resemble primates in any of the neural characteristics studied by Pettigrew, instead resembling primitive mammals such as

Insectivora The order Insectivora (from Latin ''insectum'' "insect" and ''vorare'' "to eat") is a now-abandoned biological grouping within the class of mammals. Some species have now been moved out, leaving the remaining ones in the order Eulipotyphla, w ...

in these respects. The advanced brain characters demonstrated in ''Pteropus'' could not, therefore, be generalized to imply that all bats are similar to primates. More recently, the flying primate hypothesis was soundly rejected when scientists compared the DNA of bats to that of primates. These genetic studies support the

monophyly In cladistics for a group of organisms, monophyly is the condition of being a clade—that is, a group of taxa composed only of a common ancestor (or more precisely an ancestral population) and all of its lineal descendants. Monophyletic grou ...

of bats.

Neurological studies

Soon after Pettigrew's study, work on another genus of megabat (''

Rousettus ''Rousettus'' is a genus of Old World fruit bats or megabats, referred to as rousette bats. The genus is a member of the family Pteropodidae. The genus consists of seven species that range over most of Africa to southeast Asia, and the islands ...

'') disputed the existence of an advanced pattern of connections between the

and the

. However, this conclusion was later criticised on methodological grounds. Later studies have sought further evidence of unique characteristics linking the megabat and primate brains. These studies have had limited success in identifying unique links between megabats and present-day primates, instead concluding that the megabat brain has characteristics that may resemble those likely to have existed in primitive primate brains. Nonetheless, modern neuroanatomical studies have repeatedly supported the existence of very significant differences between the brains of megabats and microbats, which is one of the anchors of the "flying primate" hypothesis.

Biochemical studies

The implication that bats are diphyletic has been fiercely disputed by many zoologists, not only based on the unlikelihood that

wing A wing is a type of fin that produces lift while moving through air or some other fluid. Accordingly, wings have streamlined cross-sections that are subject to aerodynamic forces and act as airfoils. A wing's aerodynamic efficiency is expres ...

s would have evolved twice in mammals, but also on biochemical studies of

molecular evolution Molecular evolution is the process of change in the sequence composition of cellular molecules such as DNA, RNA, and proteins across generations. The field of molecular evolution uses principles of evolutionary biology and population genetics ...

, which indicate that bats are

monophyletic In cladistics for a group of organisms, monophyly is the condition of being a clade—that is, a group of taxa composed only of a common ancestor (or more precisely an ancestral population) and all of its lineal descendants. Monophyletic gro ...

. However, other studies have disputed the validity of these conclusions. In particular, Pettigrew argued incorrectly that

phylogenies A phylogenetic tree (also phylogeny or evolutionary tree Felsenstein J. (2004). ''Inferring Phylogenies'' Sinauer Associates: Sunderland, MA.) is a branching diagram or a tree showing the evolutionary relationships among various biological spec ...

based solely on DNA data can be subject to an artifact named the "base-compositional bias" Further studies did not find base-compositional bias sufficient to discount support for the monophyly of bats.

References

{{reflist, 30em

External links

Jack Pettigrew's criticism of the molecular evidence
Primatology Bats Evolutionary biology Biological hypotheses 1758 in science