Professor Giorgio Manzi: “We're lucky we survived”
Demographic collapse has nearly wiped out man's prehistoric ancestors, scientists say. Genomics analysis shows that at least 800 thousand years ago the number of breeding individuals was reduced to only 1300.
According to scientists, the prehistoric ancestors of man were close to extinction as a result of a serious evolutionary bottleneck; approximately 800-900 thousand years ago, writes The Guardian.
A genomic analysis of more than 3,000 living humans has shown that the total population of our ancestors plummeted to about 1,280 breeding individuals in about 117,000 years. Scientists believe an extreme climate event may have created a bottleneck that nearly wiped out our lineage.
“The numbers from our study are in line with those of species that are currently threatened with extinction&rdquo ;, says Professor Giorgio Manzi, an anthropologist at the Sapienza University of Rome and senior author of the study.
However, Manzi and his colleagues believe that the existential pressure of the “bottleneck” may have triggered the emergence of a new species, Homo heidelbergensis, which is believed by some to be the common ancestor of modern humans and our “cousins” – Neanderthals and Denisovans. It is believed that Homo sapiens appeared about 300 thousand years ago.
“We are lucky to have survived, but … we know from evolutionary biology that the emergence of a new species can occur in small isolated populations,” says Professor Manzi.
Professor Chris Stringer, Head of Human Origins at the Natural History Museum in London, which was not involved in the study, notes: “This is an extraordinary period of time. It's great that we made it through. For a population of this size, one adverse climatic event, an epidemic, a volcanic eruption, is enough, and you are gone!”
This decline in population appears to coincide with major changes in global climate that have made glaciations into long-term events, a decrease in sea surface temperatures, and a possible extended period of drought in Africa and Eurasia. The team behind the work said the time window also coincides with a relatively empty period in the fossil record.
“We know that between about 900,000 and 600,000 years ago, the fossil record in Africa was very sparse, if not almost non-existent, while both before and after we have more fossil evidence,” emphasizes Professor Manzi. . – The same can be said about Eurasia: for example, in Europe we had a species known as Homo antecessor about 800,000 years ago, and then there was nothing for about 200,000 years”.
However, Professor Stringer notes that there is no conclusive evidence for a global “gap”; in the fossil record of early humans, raising the possibility that what caused the bottleneck was a more local phenomenon. “Perhaps this population bottleneck is stuck in some part of Africa surrounded by desert,” he suggests.
The paper, published in the journal Science, analyzed the genomic sequences of 3,154 people alive today from 10 African and 40 non-African populations. By studying the different versions of genes in a population, one can approximate the date when certain genes first appeared – the more time has passed, the greater the chance for the appearance of different variants of the gene. By assessing the frequency with which genes have appeared over time, scientists can gain insight into how ancestral populations have grown and shrunk over time.
The analysis found evidence of a bottleneck in all African populations, but only a weak signal about this event was found in 40 non-African populations. This is likely because the ancestors of people of non-African descent actually experienced a later demographic decline during the migration out of Africa, which is expected to mask an earlier event, writes The Guardian.
This time roughly coincides with when, it is believed, the last common ancestor roamed the Earth with the Neanderthals and another ancient species of people, the Denisovans. Now scientists want to find out if the genetic patterns of these ancient relatives are evidence of the same bottleneck, which could provide new insight into when, where and why the species diverged.