As individuals, we strive to do our best but as a branch on the evolutionary tree, humans have goofed an awful lot in Earth’s history. From eating things to extinction to cooking up emissions that in turn cook the planet, there are demonstrable examples of our boo-boos all over the place but a new study has found that there is one failing for which we aren’t to blame.
The blame for the fall of prehistoric megafaunas like the woolly mammoth, cave lion, and woolly rhinoceros at the end of the last Ice Age has often been placed on the shoulders of early humans and their spread across the globe. New research, however, published in the journal Current Biology, reveals that in the case of the woolly rhino it wasn’t actually us. How refreshing.
The researchers on the study were investigating woolly rhinoceros populations in Siberia by looking at DNA from the tissue, bone, and hair samples of 14 individuals. The DNA and mitochondrial genomes from the preserved specimens were genetically sequenced, which allowed the researchers to estimate population sizes and the genetic diversity within groups.
Their results showed that woolly rhino populations had been adapting genetically for tens of thousands of years before their extinction. Genetic indicators of their population size and estimated inbreeding rates showed that populations were stable long after humans began living in Siberia. This stability remained from 29,000 years ago, at the onset of the cold period, to 18,500 years ago when the study data set ends. Woolly rhinos didn’t go extinct until around 14,000 years ago, indicating that things changed dramatically for the species in the 4,500 years that came after the study’s range.
The gene sequencing also showed the genetic mutations that helped woolly rhinoceroses adapt to the changing climate, such as a change in a skin receptor that detected warm and cold. Woolly rhinos were well suited to the frosty northeast Siberian climate and the researchers explain this “adaptive” mutation could actually have done for the species when a brief warming period, known as the Bølling-Allerød interstadial, kicked in around the time of their extinction towards the end of the last Ice Age. Bizarrely, it wasn’t the cold of the Ice Age that finished them off but a brief burst of warmth that came before.
"It was initially thought that humans appeared in northeastern Siberia 14,000-15,000 years ago, around when the woolly rhinoceros went extinct. But recently, there have been several discoveries of much older human occupation sites, the most famous of which is around 30,000 years old," said senior author Love Dalén, a professor of evolutionary genetics at the Centre for Palaeogenetics, a joint venture between Stockholm University and the Swedish Museum of Natural History. "So, the decline towards extinction of the woolly rhinoceros doesn't coincide so much with the first appearance of humans in the region. If anything, we actually see something looking a bit like an increase in population size during this period."
However, there is more work to do to find out the details of the rhinos', and other megafaunas', decline.
"What we want to do now is to try to get more genome sequences from rhinos that are between 18,000 and 14,000 years old, because at some point, surely they must decline… We know the climate changed a lot, but the question is: how much were different animals affected, and what do they have in common?"