A Duplicate Gene May Have Helped Our Brains Become “Human”
Among the ~25,000 or so genes in our genome, we find a handful of duplicates. Some of them, like the genes that make pieces of the ribosome (your cellular protein factories) are fully-functional exact copies. This allows your cells to make a whole mess of that gene product. But other duplicates are imperfect copies put there by accidents or errors, and often those copies can be a bit wonky.
One of those imperfect gene copies may have had a strong influence on our brains becoming more advanced and “human” during evolution. A group led by Evan Eichler looked at a gene called SRGAP2 and noted that it appeared to have been duplicated to a certain form about 2.4 million years ago, which is when the Homo lineage split from Australopithecus. That duplicate, called SRGAP2C, actually overpowers the function of the original gene.
Even cooler, when Franck Polleux at Scripps expressed that SRGAP2C in mice, it made their neurons look a lot more human! So perhaps when this imperfect duplicate popped up in our genome, it changed the way our neurons developed (as shown in the picture above). If those changes were significant enough, they could have helped our larger and more advanced Homo brains evolve beyond our simpler ancestors! It’s too early to make that claim just yet, but it’s a very cool idea.
This also means that because our neurons develop in a way that is so different from mice, we should reconsider whether they are a good model for disorders like autism. We may be looking at a brain that’s just too different from our own at its core.
For more, Ed Yong has some good coverage of this on his blog.