Neuron counts reveal brain complexity evolution in land vertebrates

The evolution of brain neuron numbers in amniotes was reconstructed by researchers from the Charles University in Prague. According to these findings, there are only a few major changes in the brain's scaling in over 300 million years of evolution that paved the way to bird and mammal intelligence.

Data on brain size has traditionally been used to infer the evolution of brain processing capacity. Similar sized brains of distantly related species can differ in the number and distribution of their basic computational units. We need to compare brains not by mass but by the number of neurons to see the evolutionary path to increased cognitive capacity.

Researchers analyzed brain cellular composition across amniotes using a new, comprehensive dataset. The telencephalon and cerebellum, which are brain parts associated with higher cognitive function, have increased in mammals and birds. An analysis shows that only a few major changes in brain scaling in over 300 million years of evolution paved the way to intelligence.

Using the largest dataset of its kind and including essential data on reptiles, our study reconstructs the evolution of brains across amniotes by directly analyzing neuron numbers. The results show that a few unique evolutionary events increased brain power in birds and mammals. One of the authors of the study says that it does not come as a surprise that high intelligence is a rare capacity.

The research shows that reptile brains are smaller than those in birds and mammals, and that the average number of neuron numbers is 20 times lower in reptile brains than in birds and mammals. The Amniote brain evolution is characterized by four major shifts.

The appearance of birds and mammals resulted in convergent neuron scaling in the two endotherm lineages. It seems that endothermy, an expensive mode of life, enabled this gain. Brain evolution is influenced by energetic constraints. The increase in the number of neurons happened in two groups that are known for their cognitive prowess.

Relative brain size is not associated with cell density in other mammals. This has important implications for studies using relative brain size as a proxy when looking for evolutionary drivers of animal cognitive function.

More information: The evolution of brain neuron numbers in amniotes, PNAS (2022). DOI: 10.1073/pnas.2121624119 Journal information: Proceedings of the National Academy of Sciences Citation: Neuron counts reveal brain complexity evolution in land vertebrates (2022, March 8) retrieved 8 March 2022 from https://phys.org/news/2022-03-neuron-reveal-brain-complexity-evolution.html This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only.