The
flying primates theory conjectures that
megabatMegabats is the term used informally to refer to bats of the family Pteropodidae . They are also referred to as fruit bats, old world fruit bats, or flying foxes...
s, a sub-group of Chiroptera (also known as flying foxes), form an evolutionary sister group of
PrimateA primate is a member of the biological order Primates , the group that contains lemurs, lorisids, galagos, tarsiers, monkeys, and apes, with the last category including great apes. With the exception of humans, who inhabit every continent on Earth, most primates live in tropical or subtropical...
s. This theory was proposed by Australian neuroscientist
Jack PettigrewJohn Douglas Pettigrew is Emeritus Professor of Physiology and Director of the Vision, Touch and Hearing Research Centre at the University of Queensland in Australia.Professor Pettigrew's research interest is in comparative neuroscience...
in 1986 after discovering that the connections between the
retinaThe vertebrate retina is a light sensitive tissue lining the inner surface of the eye. The optics of the eye create an image of the visual world on the retina, which serves much the same function as the film in a camera. Light striking the retina initiates a cascade of chemical and electrical...
and the
superior colliculusThe optic tectum or simply tectum is a paired structure that forms a major component of the vertebrate midbrain. In mammals this structure is more commonly called the superior colliculus , but even in mammals, the adjective tectal is commonly used. The tectum is a layered structure, with a number...
(a region of the midbrain) in the megabat
PteropusBats of the genus Pteropus, belonging to the Megachiroptera sub-order, are the largest bats in the world. They are commonly known as the Fruit Bats or Flying Foxes among other numerous colloquial names...
were organized in the same way found in primates, and different from all other
mammalMammals are a class of vertebrate animals whose females are characterized by the possession of mammary glands while both males and females are characterized by sweat glands, hair, three middle ear bones used in hearing, and a neocortex region in the brain.Mammals are divided into three main...
s.
The
flying primates theory conjectures that
megabatMegabats is the term used informally to refer to bats of the family Pteropodidae . They are also referred to as fruit bats, old world fruit bats, or flying foxes...
s, a sub-group of Chiroptera (also known as flying foxes), form an evolutionary sister group of
PrimateA primate is a member of the biological order Primates , the group that contains lemurs, lorisids, galagos, tarsiers, monkeys, and apes, with the last category including great apes. With the exception of humans, who inhabit every continent on Earth, most primates live in tropical or subtropical...
s. This theory was proposed by Australian neuroscientist
Jack PettigrewJohn Douglas Pettigrew is Emeritus Professor of Physiology and Director of the Vision, Touch and Hearing Research Centre at the University of Queensland in Australia.Professor Pettigrew's research interest is in comparative neuroscience...
in 1986 after discovering that the connections between the
retinaThe vertebrate retina is a light sensitive tissue lining the inner surface of the eye. The optics of the eye create an image of the visual world on the retina, which serves much the same function as the film in a camera. Light striking the retina initiates a cascade of chemical and electrical...
and the
superior colliculusThe optic tectum or simply tectum is a paired structure that forms a major component of the vertebrate midbrain. In mammals this structure is more commonly called the superior colliculus , but even in mammals, the adjective tectal is commonly used. The tectum is a layered structure, with a number...
(a region of the midbrain) in the megabat
PteropusBats of the genus Pteropus, belonging to the Megachiroptera sub-order, are the largest bats in the world. They are commonly known as the Fruit Bats or Flying Foxes among other numerous colloquial names...
were organized in the same way found in primates, and different from all other
mammalMammals are a class of vertebrate animals whose females are characterized by the possession of mammary glands while both males and females are characterized by sweat glands, hair, three middle ear bones used in hearing, and a neocortex region in the brain.Mammals are divided into three main...
s. This was followed up by a longer study published in 1989, in which this was supported by the analysis of many other
brainThe brain is the center of the nervous system in all vertebrate, and most invertebrate, animals. Some primitive animals such as jellyfish and starfish have a decentralized nervous system without a brain, while sponges lack any nervous system at all...
and body characteristics. Pettigrew suggested that flying foxes,
colugoColugos are arboreal gliding mammals found in South-east Asia. There are just two extant species, which make up the entire family Cynocephalidae and order Dermoptera. They are the most capable of all gliding mammals, using flaps of extra skin between their legs to glide from higher to lower...
s and primates were all descendants of a same group of early arboreal mammals. The megabat flight and the colugo
glidingGliding is a recreational activity and competitive sport in which pilots fly unpowered aircraft known as gliders using rising air to gain altitude or speed. The word soaring is also used for the sport...
could be both seen as locomotory adaptations to a life high above the ground.
The flying primate theory 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 shrews, colugos and
batBats are flying mammals in the order Chiroptera . The forelimbs of bats are webbed and developed as wings, making them the only mammals naturally capable of true and sustained flight. By contrast, other mammals said to fly, such as flying squirrels, gliding possums and colugos, glide rather than...
s under a same taxonomic group, the Superorder
ArchontaThe Archonta are a group of mammals considered a superorder in some classifications.The Archonta consist of the following orders :*Primates*Plesiadapiformes *Scandentia *Dermoptera...
). Rather, many biologists resisted the implication that megabats and
microbatThe microbats constitute the suborder Microchiroptera within the order Chiroptera . They are most often referred to by their scientific name...
s (or echolocating bats) formed distinct branches of mammalian
evolutionIn biology, evolution is change in the genetic material of a population of organisms from one generation to the next. Though changes produced in any one generation are normally small, differences accumulate with each generation and can, over time, cause substantial changes in the population, a...
, with flight having
evolved twiceConvergent evolution describes the acquisition of the same biological trait in unrelated lineages.The wing is a classic example of convergent evolution in action. Although their last common ancestor did not have wings, birds and bats do, and are capable of powered flight. The wings are similar in...
. 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
InsectivoraThe order Insectivora is a now-abandoned biological grouping within the class of mammals....
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 primates hypothesis was rejected when scientists compared the DNA of bats to that of primates. These genetic studies support the monophyly of bats.
Neurological studies
Soon after Pettigrew's study, work on another genus of megabat (
RousettusRousettus is a genus of Old World fruit bats. They are sometimes referred to as dog-faced fruit bats, or flying foxes. The genus is a member of the suborder Megachiroptera...
) disputed the existence of an advanced pattern of connections between the
retinaThe vertebrate retina is a light sensitive tissue lining the inner surface of the eye. The optics of the eye create an image of the visual world on the retina, which serves much the same function as the film in a camera. Light striking the retina initiates a cascade of chemical and electrical...
and the
superior colliculusThe optic tectum or simply tectum is a paired structure that forms a major component of the vertebrate midbrain. In mammals this structure is more commonly called the superior colliculus , but even in mammals, the adjective tectal is commonly used. The tectum is a layered structure, with a number...
. 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 primates" theory.
Biochemical studies
The implication that bats are diphyletic has been fiercely disputed by many zoologists, not only based on the unlikelihood that
wingA wing is a surface used to produce lift for flight through the air or another gaseous or fluid medium. The wing shape is usually an airfoil. The word originally referred only to the foremost limbs of birds, but has been extended to include the wings of insects , bats, pterosaurs, and aircraft.A...
s would have evolved twice in mammals, but also on biochemical studies of molecular evolution, which indicate that bats are monophyletic. However, other studies have disputed the validity of these conclusions. In particular, it has been argued that phylogenies that are based solely on DNA data can be subject to an artifact named the "base-compositional bias"
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