Scientists continue to investigate ancient DNA to see how it might affect the body shape of extinct hominids. Recent results of a study, which has not yet been published, have shown that Neanderthal and Denisovan genes can cause different physical changes in mice. Using CRISPR gene-editing technology, scientists introduced the ancient genetic code into rodents and found that this led to the development of large heads, curved ribs and shortened spines in the animals.
The gene being studied, known as GLI3, plays an important role in the embryonic development of modern humans. Mutations in this gene are associated with physical malformations such as polydactyly and skull deformity. It is interesting to note that both Neanderthals and Denisovans carried a slightly altered version of the GLI3 gene, but they did not have an abnormal number of fingers or dangerous skull defects.
However, these extinct hominid species exhibited other morphological characteristics that differed from modern humans. They had elongated and low skulls, large brow arches, and broader thoraxes. To understand how an ancient form of the GLI3 gene might have influenced the development of these species, scientists conducted experiments on mice.
Scientists engineered mice with a defective version of the GLI3 gene and found that they developed severe skull and brain deformities, as well as polydactyly. This confirms that a functioning version of the gene is necessary for healthy embryonic growth. They then created mice with a version of the gene possessed by Neanderthals and Denisovans and found altered skeletal structures, an enlarged skull, altered vertebral shapes and rib malformations.
Comparing these results to normal mice, the scientists noticed that mice with the archaic gene had fewer vertebrae and more twisted ribs, reflecting differences between modern humans and Neanderthals. Some of these mice also exhibited an asymmetrical thorax shape associated with scoliosis. This is interesting because recent studies have shown that Neanderthals may have been prone to scoliosis and an enlarged head size.
Overall, the archaic version of the GLI3 gene carried by Neanderthals and Denisovans may have been partly responsible for their distinctive head and body shapes. These traits are related to the predicted lifestyle of Neanderthals, suggesting that the ancient gene provided useful traits for extinct hominids.
This study, which is awaiting review, is available as a preprint on the bioRxiv website.