Today’s 7.5 billion people on Earth probably descended from a small population that survived a near-extinction event within the past few hundred thousand years, scientists from the US and Switzerland have concluded.
The study shows that nine out of ten species on Earth today, including humans, came into being 100,000 to 200,000 years ago. The study was published by researchers at The Rockefeller University in New York and the University of Basel in Switzerland in the journal Human Evolution back in May.
“Was there some catastrophic event 200,000 years ago that nearly wiped the slate clean?” asked a report in Agence France-Presse at the time.
They posited that each species has had almost all its genetic diversity purged, which implies that its population was once very small.
The study has gained wider currency this week, with popular media latching on to the idea that it showed all modern humans descended from a solitary pair – an Adam and Eve.
However, the original paper does not make this claim. If anything, the “catastrophic event” the report posits brings to mind the Bible’s account of Noah’s flood, which wiped out all species on earth except for those in the ark.
The paper says:
“Scholars have previously argued that 99 per cent of all animal species that ever lived are now extinct. Our work suggests that most species of animals alive today are, like humans, descendants of ancestors who emerged from small populations, possibly with near-extinction events within the past few hundred thousand years.”
The paper reported on new insights into evolution gained from examining the mitochondrial DNA from about five million specimens covering about 100,000 animal species. These specimens have been assembled by scientists worldwide over the past 15 years in the GenBank database maintained by the US National Centre for Biotechnology Information.
“If a Martian landed on Earth and met a flock of pigeons and a crowd of humans, one would not seem more diverse than the other.” – Jesse Ausubel
After examining the range of genetic differences within animal species ranging from bumblebees to birds, the researchers were surprised to discover that there were only minute genetic variations within most animal species, while on the other hand there were very clear distinctions between a given species and all others.
The study is based on DNA barcoding which is a technique of reading a small piece of an organism’s DNA and using that to identify its specifies. An animal is generally identified by a gene called cytochrome oxidase 1 (CO1) which is not part of the main genome in the cell nucleus but carried in the mitochondria, which swarm inside animal cells and provide them with energy.
Because CO1 genes are so similar within species – regardless of the size of the population – the researchers argued that something made them that way. They posited that each species has had almost all its genetic diversity purged, which implies that its population was once very small. These population bottlenecks seemingly all occurred between 100,000 and 200,000 years ago, which implies some sort of global catastrophe that slashed the population of almost every animal species.
“If a Martian landed on Earth and met a flock of pigeons and a crowd of humans, one would not seem more diverse than the other, according to the basic measure of mitochondrial DNA,” says Jesse Ausubel, Director of the Program for the Human Environment at the Rockefeller University, where the research was led by Mark Stoeckle and the University of Basel’s David Thaler.
“At a time when humans place so much emphasis on individual and group differences, maybe we should spend more time on the ways in which we resemble one another.”