Humans share almost all of their genes with chimpanzees. But humans have bigger and more wrinkled brains than chimps and other close relatives (see Why wrinkles make us human – MPI TalkLing and How does your brain grow differently from a mouse? – MPI TalkLing). Which genes play a role in that? Time for a meet-and-greet.
What is a gene?
But first, what is a gene? Philosophical discussion aside, a gene is a part of our DNA which in most cases provides the code to build a protein, a tiny machine inside your cells, for example a handy molecule to bring glucose (sugar) into your cells to burn as fuel. To keep a cell running, you need many such handy molecules for all sorts of things. The thing is, when we look at something as complicated as a wrinkly brain, or even more complicated like language, there are many genes that influence this. For example, a better functioning glucose transporter may lead to more glucose in your cell. That cell might divide slightly easier, leading to more cells. So going from a gene to a higher-level property often becomes complicated very quickly.
Genes can sometimes have names that sound as if they come from a science fiction novel. This is the case with several of the genes thought to be important in human brain evolution: ARHGAP11B and NOTCH2NL for example, which appear specific to humans.
Wrinkles from Neanderthals
To start at the beginning, ARHGAP11B is a gene found in humans and in Neanderthals, but not in chimpanzees. The gene causes an increase of basal radial glial cells, (from blog 2) in early human brain development, by making the energy factories of the cell, called mitochondria, work better. When scientists activate this gene in animals, it leads to thicker brains in mice, marmosets and ferrets and even causes wrinkly features in mice and marmosets. In other words, their brains become more human-like.
Weird cousin
The weird cousins of our human gene family are the NOTCH2NL gene family. They are truncated versions of their “mother”, the NOTCH2 receptor. They help their mother do her job better, assisting in a process called NOTCH signaling, which leads to more basal radial glial cells, and therefore later more brain cells. Scientists are not sure yet if this also leads to more wrinkly brains, but it definitely means bigger brains.
Another reason to love your grandpa
These are just two genes, but they are unique to humans and seem to give us bigger and more wrinkled brains. There’s much more to the evolution of language and music, but the story of being human begins to look an awful lot like the skin of our grandpas.
References
https://www.cell.com/developmental-cell/pdf/S1534-5807(23)00580-4.pdf
https://journals.sagepub.com/doi/full/10.1177/10738584231190839
https://www.science.org/doi/full/10.1126/science.abb2401
https://www.cell.com/fulltext/S0092-8674(18)30383-0
https://doi.org/10.1016/j.neuron.2019.11.027
https://www.science.org/doi/10.1126/science.aaa1975
