Abstract:

Over the past 5 to 7 million years, humans and chimpanzees have diverged in brain size, structure, and cognition despite high conservation of protein-coding genes. However, retroviral infections within host genomes have introduced numerous species-specific regulatory elements. Chimpanzees harbor lineage-specific PTERV1 endogenous retroviruses that are absent in humans, but their role in brain evolution has remained unclear. We performed an epigenomic analysis of PTERV1 insertions in chimpanzee neural organoids and found they are heavily DNA methylated, forming over 150 species-specific heterochromatin domains with the potential to influence gene regulation. We identified a chimpanzee-specific insertion on chromosome 19 that silences the long noncoding RNA LINC00662 through DNA methylation spreading. CRISPR-mediated deletion of this PTERV1 restored LINC00662 expression in chimpanzee induced pluripotent stem cells. We show that LINC00662, a human-specific transcript expressed during brain development, plays a role in neuronal maturation, axon outgrowth, and neural organoid development. These findings reveal a mechanism by which endogenous retroviral insertions contributed to human-chimpanzee brain divergence.

I've read years ago about a DNA sequence that allows humans to form up to 7 connections per neuron, while chimpanzees are limited to 4 (with the downside of more neuronal malfunctions in humans). Is it about this?

Fire up them retros, its time for some evolution!

Not sure about the genes affecting connectivity, but I can tell you that neurons in both chimpanzees and humans connect to wayyy more than 7 neurons. Like orders of magnitude more. In the Prefrontal Cortex, pyramidal neurons can have upwards of 30,000 excitatory inputs alone

Dendrites are the inputs; axons are the outputs. Both tend to branch and each dendrite has many “spines” which form the input synapses.

But yes, that sounds more likely since it is theorized that the basal dendrites in the prefrontal cortex being larger and more complex than others is what allows them to integrate larger amounts of information and could correlate with intelligence.

If it's not we got something from virus that helped us, and chimps got something that limited them. Then it's funnily possible for a global pandemic to make our whole population stupid. Normally evolution would work out and smarter population would do better, but for us it depends on which side has nukes. So ...

Then it's funnily possible for a global pandemic to make our whole population stupid.

Still, just from my gut feeling, this seems like a very convincing explanation to whatever is happening in the world in the last years.