Relatively speaking, modern humans are newcomers to the planet. Our species also dispersed and expanded across the globe quite quickly. Together, these two factors led to relatively low genetic diversity in modern humans. Chimpanzees, gorillas, orangutans, and some gibbons, on the other hand, have higher genetic variability within each species. These apes also show more variability than humans in certain skeletal traits, such as skull shape.
Traditionally, genetic variation and skeletal diversity have been analyzed separately, but now, by looking at genetics together with skull shape, a new study led by Museum researchers has found an intriguing evolutionary pattern across the ape family tree—one that has potential applications in studying the extinct species of the hominin family tree.
The work, led by Julia Zichello, the Museum’s assistant director of the Sackler Educational Laboratory for Comparative Genomics and Human Origins, compared skull shape and genetics of 12 modern ape species. “We found a strong pattern that species that are more genetically diverse are also more cranially diverse,” Zichello said.
This previously unrecognized pattern is likely due to “neutral” evolutionary factors like genetic drift, mutation, and changes in population size through time, instead of natural selection. “Natural selection is often thought about as the main force of evolution, but there are a number of other forces that are more random in nature, that aren’t necessarily the result of something that’s beneficial for a species,” Zichello says. “And that’s what we think is related to this pattern of ape cranial shape diversity.”
One of the applications of these findings could be to the field of paleoanthropology, where researchers use comparative anatomy to study extinct human relatives by looking at similarities between living ape species and, often fragmentary, fossils of hominin ancestors.
The relationship between genetic and cranial diversity among living ape species could provide valuable insights to better understand the fossil record. “Living ape species are often used as a guide for extinct diversity,” Zichello says. “And if you’re doing that, you need to know as much about that living species as you can, including what evolutionary processes have contributed to the observed levels of variation we see today.”