Big brains are all in the genes

Nov 28, 2013 by Marie Daniels
Big brains are all in the genes

Scientists have moved a step closer to understanding genetic changes that permitted humans and other mammals to develop such big brains.

During evolution, different mammal species have experienced variable degrees of expansion in size. An important goal of neurobiology is to understand the underlying these extraordinary adaptations.

The process by which some species evolved larger brains – called encephalization – is not well understood by scientists. The puzzle is made more complex because evolving large brains comes at a very high cost.

Dr Humberto Gutierrez, from the School of Life Sciences, University of Lincoln, UK, led research which examined the genomes of 39 species of mammals with the aim of better understanding how brains became larger and more complex in mammals.

To do this, the scientists focussed on the size of across these species. Gene families are groups of related genes which share similar characteristics, often linked with common or related . It is believed that large changes in the size of gene families can help to explain why related species evolved along different paths.

The researchers found a clear link between increased brain size and the expansion of gene families related to certain biological functions.

Dr Gutierrez said: "We found that brain size variations are associated with changes in gene number in a large proportion of families of closely related genes. These gene families are preferentially involved in cell communication and cell movement as well as immune functions and are prominently expressed in the human brain. Our results suggest that changes in gene family size may have contributed to the evolution of larger brains in mammals."

Mammalian species in general tend to have large brains compared to their body size which represent an evolutionary costly adaptation as they require large amounts of energy to function.

Dr Gutierrez explained: "The brain is an extremely expensive organ consuming a large amount of energy in proportion to its volume, so large brains place severe metabolic demands on animals. Larger brains also demand higher parental investment. For example, humans require many years of nurturing and care before their brains are fully matured."

Dr Gutierrez's research concluded that variations in the size of gene families associated with encephalization provided an evolutionary support for the specific physiological demands associated with increased in mammals.

Explore further: Different gene expression in male and female brains may help explain sex differences in brain disorder

More information: 'Increased brain size in mammals is associated with size variations in gene families with cell signalling, chemotaxis and immune-related functions' Humberto Gutiérrez, Atahualpa Castillo-Morales, Jimena Monzón-Sandoval and Araxi O. Urrutia, Proc. R. Soc. B 2014 281, 20132428, published 27 November 2013, rspb.royalsocietypublishing.or… 132428.full.pdf+html

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1 / 5 (7) Nov 28, 2013
Journal article conclusion: "...variations in GFS associated with encephalization provided an evolutionary support for the specific cellular, physiological and developmental demands associated with increased brain size in mammals."

If "Big Brains Are All in the Genes" was an appropriate title, variations would be causal -- not merely associated with what most people know are epigenetic effects of the sensory environment on biophysically constrained specific cellular, physiological, and developmental changes that link the epigenetic landscape to the physical landscape of DNA in the organized genomes of species from microbes to man via conserved molecular mechanisms.

Thus, what's represented in the journal article, and more explicitly in the journalist's report is akin to "Evolution for Dummies" in which genes are determinants of brain size outside the context of olfactory/pheromonal input that alters ecological, social, neurogenic, and socio-cognitive niche construction.
Nov 28, 2013
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1 / 5 (7) Nov 28, 2013
MicroRNA-Driven Developmental Remodeling in the Brain Distinguishes Humans from Other Primates

Tissue-specific changes in the expression of trans-regulators, such as miRNA, rather than sequence changes in cis-regulatory regions, are the driving force underlying developmental remodeling across hundreds of genes.

Clearly, Big Brains are not all in the genes, or the remodeling would not involve changes in the microRNA/messenger RNA balance that result in difference in human and non-human primate brains, insect brains, and in nematode neurogenic niche construction.
5 / 5 (2) Nov 28, 2013
So why then do so many people have such small ones? lol