evolutionary biology Evolutionary biology is the subfield of biology that studies the evolutionary processes such as natural selection, common descent, and speciation that produced the diversity of life on Earth. In the 1930s, the discipline of evolutionary biolo ...

, the flying primate hypothesis is that

megabat Megabats constitute the Family (biology), family Pteropodidae of the Order (biology), order Chiroptera. They are also called fruit bats, Old World fruit bats, or—especially the genus, genera ''Acerodon'' and ''Pteropus''—Pteropus, flyin ...

s, a subgroup of

Chiroptera Bats are flying mammals of the order Chiroptera (). 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 birds, flying with their very long spread-out ...

(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 ...

primate Primates is an order (biology), order of mammals, which is further divided into the Strepsirrhini, strepsirrhines, which include lemurs, galagos, and Lorisidae, lorisids; and the Haplorhini, haplorhines, which include Tarsiiformes, tarsiers a ...

s. The

hypothesis A hypothesis (: hypotheses) is a proposed explanation for a phenomenon. A scientific hypothesis must be based on observations and make a testable and reproducible prediction about reality, in a process beginning with an educated guess o ...

began with

Carl Linnaeus Carl Linnaeus (23 May 1707 – 10 January 1778), also known after ennoblement in 1761 as Carl von Linné,#Blunt, Blunt (2004), p. 171. was a Swedish biologist and physician who formalised binomial nomenclature, the modern system of naming o ...

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 specializing in neuroscience that deals with the anatomy and function of neurons, Biological neural network, neural circuits, and glia, and their Behavior, behavioral, biological, and psycholo ...

Jack Pettigrew in 1986 after he discovered that the connections between the

retina The retina (; or retinas) is the innermost, photosensitivity, light-sensitive layer of tissue (biology), tissue of the eye of most vertebrates and some Mollusca, molluscs. The optics of the eye create a focus (optics), focused two-dimensional ...

and the

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

(a region of the

midbrain The midbrain or mesencephalon is the uppermost portion of the brainstem connecting the diencephalon and cerebrum with the pons. It consists of the cerebral peduncles, tegmentum, and tectum. It is functionally associated with vision, hearing, mo ...

) 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, Aust ...

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

mammal A mammal () is a vertebrate animal of the Class (biology), class Mammalia (). Mammals are characterised by the presence of milk-producing mammary glands for feeding their young, a broad neocortex region of the brain, fur or hair, and three ...

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

brain The brain is an organ (biology), organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It consists of nervous tissue and is typically located in the head (cephalization), usually near organs for ...

and body characteristics. Pettigrew suggested that flying foxes,

colugo Colugos (), flying lemurs, or cobegos (), are arboreal gliding euarchontogliran 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 ...

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

arboreal Arboreal locomotion is the 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 (scansorial), but others are exclusively arboreal. The hab ...

mammals. The megabat flight and the colugo

gliding Gliding is a recreational activity and competitive air sports, air sport in which pilots fly glider aircraft, unpowered aircraft known as Glider (sailplane), gliders or sailplanes using naturally occurring currents of rising air in the atmospher ...

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 (also called tree shrews or banxrings) are small mammals native to the tropical forests of South and Southeast Asia. They make up the entire Order (biology), order Scandentia (from Latin ''scandere'', "to climb"), which split into ...

s, colugos, and

bat Bats are flying mammals of the order Chiroptera (). 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 birds, flying with their very long spread-out ...

s under the same taxonomic group, the

Superorder Order () 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 recognized ...

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 an ...

s (or echolocating bats) formed distinct branches of mammalian

evolution Evolution is the change in the heritable Phenotypic trait, characteristics of biological populations over successive generations. It occurs when evolutionary processes such as natural selection and genetic drift act on genetic variation, re ...

, 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 (biology), 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 ...

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 biological cladistics for the classification of organisms, monophyly is the condition of a taxonomic grouping being a clade – that is, a grouping of organisms which meets these criteria: # the grouping contains its own most recent comm ...

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_(biology), family Pteropodidae. The genus consists of seven species that range over most of Africa to southeast Asia, ...

'') 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 both Lift (force), lift and drag while moving through air. Wings are defined by two shape characteristics, an airfoil section and a planform (aeronautics), planform. Wing efficiency is expressed as lift-to-d ...

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

molecular evolution Molecular evolution describes how Heredity, inherited DNA and/or RNA change over evolutionary time, and the consequences of this for proteins and other components of Cell (biology), cells and organisms. Molecular evolution is the basis of phylogen ...

, which indicate that bats are

monophyletic In biological cladistics for the classification of organisms, monophyly is the condition of a taxonomic grouping being a clade – that is, a grouping of organisms which meets these criteria: # the grouping contains its own most recent co ...

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

phylogenies A phylogenetic tree or phylogeny is a graphical representation which shows the evolutionary history between a set of species or taxa during a specific time.Felsenstein J. (2004). ''Inferring Phylogenies'' Sinauer Associates: Sunderland, MA. In o ...

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

Neurological studies

Biochemical studies

See also

References

External links