International research groups such as the Graduate University for Advanced Studies have found that in mammals and birds, brain growth is separated from body growth, and that large mammals and birds have an extended early development period with rapid brain development. For the first time in the world, I discovered that it has evolved.

 Mammals and birds, including humans, are 10 to 20 times larger in brain than fish and amphibians of the same size.This is the reason why many mammals and birds have high learning ability and sociality.Previous studies have cited methods of brain development as factors that control the path of major evolution of the brain, but this hypothesis has not been tested.

 Through museum research and literature research, the research group collected data on brain size and body size of more than 2 individuals and 4500 species in collaboration with collaborators from around the world.For the first time, it was shown that the relationship (allometry) that large animals have a large brain and small animals have a small brain is common to all vertebrates.Furthermore, we investigated in detail how the relationship between body size and brain size differs between birds / mammals and other taxa.

 As a result, it was found that in birds and mammals, the adult brain size is almost constant regardless of the body size.This indicates that the brain develops independently of body growth.In mammals, birds, and fish, the brain size grows rapidly from the early stage of development until it reaches a certain size, and then the growth of the brain size declines and the growth of the body size accelerates to become an adult. It turns out that it takes a two-stage structure.On the other hand, unlike fish, mammals and birds have succeeded in significantly prolonging the accelerated growth period accompanied by rapid brain growth and greatly evolving brain size without changing body size.

Paper information:[Nature Ecology & Evolution] Breakdown of allometry and encephalization of birds and mammals

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