Whenever people think of Neanderthals, they probably picture a caveman in dire need of a haircut. However, there is something more to the typical appearance of Neanderthals, especially in their faces.
Features such as large noses, prominent brow ridges, and a strong lower jaw gave them a distinctive appearance. But since the Neanderthal genome is 99.7 percent identical to the human genome, why were their faces so different from ours?
New research published in the journal Development cracked part of the code of Neanderthal faces by studying their genome. Although the Neanderthal and human genomes overlap in many places, a tiny piece of Neanderthal DNA plays a special role in the growth of their large mandibles. This key difference now explains at least one reason why Neanderthal faces are different from ours.
Read more: How much Neanderthal DNA do humans have?
Unraveling the Neanderthal genome
In 2010, the first Neanderthal genome was sequenced using 21 ancient bones from Vindija Cave in Croatia. This breakthrough opened up new possibilities in the field of evolutionary genetics, allowing scientists to compare Neanderthal genes with human genes. It has also been conclusively confirmed that many humans have genetic ancestry from Neanderthals due to crossing between the two groups around 50,500–43,500 years ago.
Both Neanderthal and human genomes consist of approximately 3 billion letters (or bases) of DNA. The order of these letters determines which amino acids will be incorporated into the protein structure and also determines how certain genes are activated.
Researchers involved in the new study sought to find the specific part of the Neanderthal genome that influences their jaw size. However, sifting through 3 billion emails is like trying to find a needle in a haystack, as described in press release at school. Luckily, the researchers had a plan to make their search less stressful.
Special sequence
To solve the problem of finding the right region of the Neanderthal genome, the researchers turned to a specific region associated with the Pierre Robin sequence, a rare birth defect that causes people's lower jaws to be disproportionately small.
“Some people with the Pierre Robin sequence have large DNA deletions or rearrangements in this part of the genome that alter facial development and limit jaw formation. We predicted that smaller differences in DNA could have more subtle effects on facial shape,” said author Hannah Long, a geneticist at the University of Edinburgh.
They found that the Neanderthal and human versions of this region of the genome, only about 3,000 letters long, had just three single-letter differences. There are no genes in this region, but it regulates how and when a specific gene called SOX9, which is involved in facial development, is activated.
A colorful look at Neanderthal genes
The researchers focused on the unique writings of Neanderthals and their influence on embryonic development. They inserted Neanderthal and human versions of the region into DNA zebrafish — which have clear, easy-to-observe embryos — and programmed the zebrafish cells to produce different colors of fluorescent protein depending on which version was active.
While observing the development of zebrafish embryos, the researchers noticed that both the human and Neanderthal regions were active in cells associated with the formation of the lower jaw, with the Neanderthal region being much more active.
“It was very exciting when we first observed activity in the developing zebrafish snout in a specific population of cells close to the developing jaw, and even more so when we noticed that Neanderthal-specific differences could alter its activity during development,” Long said.
The researchers also inserted additional SOX9 genes inside the embryos to see if increased activity in the Neanderthal region would change the shape and function of the adult jaw. In doing so, they eventually discovered that the cells associated with jaw development occupy a larger area.
Now that researchers have identified the reason Neanderthals have larger mandibles, they are studying how different parts of the genome are connected to other parts of the genome. features.
Read more: Neanderthal vs. Homo Sapiens: How are Neanderthals different from humans?
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