Scientists Compare Brain Development Between Us and Neanderthals
Tiny changes between the brains of modern humans and neanderthals make a big difference
Hiya!
We modern humans are just one of many Human species that have lived on this planet. Research shows that not only did we co-exist with other Human species like the Neanderthals and Denisovians, but we also bred with them and had offspring. That said, we’re the last Humans standing, so to speak, and we’ve often wondered why. What set us apart from other Human species? What advantages did we have that allowed us to flourish when all the rest perished?
Well, scientists recently discovered that specific neural stem cells in modern humans spend more time preparing their chromosomes for division than in Neanderthals. This might not seem like a big deal and is likely less enticing than the assumption we killed off the Neanderthals due to blood lust, but such a small change likely resulted in fewer errors during cell division which impact how the brain develops and functions.
A Little Bit of Science
The largest and most visible part of our brain is called the cerebral cortex — it’s the wrinkly outer layer, also called grey matter, that most, if not all, mammals have. It also happens to be highly involved in various cognitive capabilities, including learning, problem-solving, memory, reasoning, thinking, consciousness, processing our emotions, and multiple functions involving our senses.
Within the cerebral cortex is the neocortex — “neo” means “new” — so named because experts believe this region is relatively new in vertebrate evolution. The neocortex is believed to play a role in attention, perception, thought, and memory. In humans, about 90 percent of our cerebral cortex is taken up by the neocortex.
Experts know the neocortex expanded dramatically throughout human evolution, including in ancient human species related to both us modern Humans and our Human cousins, the Neanderthals. This resulted in our two species having similar-sized brains, but little to nothing is known about any similarities or differences in how our brains developed or functioned between the two species.
However, since scientists sequenced the Neanderthal genome in 2010, we know that about 100 amino acids — the building blocks of proteins in our cells and tissue — changed when our modern human ancestors split from the Neanderthal and Denisovan lineages, and these changes continued to spread among modern humans.
While amino acid substitutions can have significant effects, the role, or biological significance, of these changed amino acids between modern humans and Neanderthals is a mystery scientists have been trying to solve since their discovery.
In the process, experts have identified six amino acid substitutions in three specific proteins that are involved in distributing chromosomes to the two daughter cells that arise when a cell divides.
Chromosomes are always interesting because they carry our genetic information. When a cell divides, one of its primary responsibilities is to ensure that each of the two new cells (called daughter cells) receives a perfect copy of the genetic information.
Mistakes during this process, such as producing unequal genetic material between the daughter cells, can lead to unhealthy cells and may result in diseases like cancer.
So, German researchers from the Max Planck Institute of Molecular Cell Biology and Genetics in Dresden and the Max Planck Institute for Evolutionary Anthropology in Leipzig wanted to study the significance of these six amino acids for neocortex development. They published their findings in Science Advances in July 2022.
The Study
To study the relationship between the neocortex and these six amino acids, the researchers introduced the modern human amino acid variants to mice using CRISPR Cas-9. They used mice because, like Neanderthals, mice share those same six amino acids within the relevant proteins.
Felipe Mora-Bermúdez, the lead author of the study, describes what they discovered in a press release about the study:
"We found that three modern human amino acids in two of the proteins cause a longer metaphase, a phase where chromosomes are prepared for cell division, and this results in fewer errors when the chromosomes are distributed to the daughter cells of the neural stem cells, just like in modern humans."
Next, the researchers wanted to flip things around and see if the Neanderthal set of amino acids had the opposite effect. So, instead of mice, the scientists introduced the ancestral amino acids to human brain organoids that were grown in a lab using human stem cells in cell culture dishes. This time, according to Mora-Bermúdez:
"Metaphase became shorter and we found more chromosome distribution errors."
In other words, the results suggest that the three amino acid changes within the proteins are likely responsible for dividing chromosomes with fewer errors in modern humans compared to Neanderthals.
The discrepancy shows that these tiny changes allow the cells of modern humans to take a little more time before dividing and thus produce fewer errors when doing so.
Since Neanderthals and modern Humans had similar brain sizes, Wieland Huttner, who co-supervised the study, reports that the study’s results imply that certain aspects of brain evolution and function occur independently from brain size. The study also suggests that Neanderthal brain function could have been more affected by chromosome errors.
Perspective Shift
Rather than bloodshed and violence, it was more likely having sex with us that resulted in the dwindling of Neandetheral populations. When our genetic lines mixed, it led to an untold number of small biological changes that allowed our modern human species to thrive, while Neanderthals and other human species weren’t so lucky. This just goes to show that sometimes the smallest change can lead to huge impacts.
These tiny changes within our amino acids gave us an edge our Human cousins didn’t have. Allowing just a little more time for cells to prepare for division results in fewer chromosome errors, and over time, this ultimately leads to healthier populations.
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I suspected as much, thanks for detailing this.
“This just goes to show that sometimes the smallest change can lead to huge impacts.”
Like a mere 1 degree rise (doesn’t sound like much) in global temperatures can have such a dramatic effect!
Whoa, heady stuff! Nice job! I disagree, though, with scientists who believe Neanderthals are extinct. I've known a number of them during my life. ;-)