An important step forward in the understanding of human evolution comes from a genetic and anthropological study, published in the international journal Science, comprising Chinese and Italian researchers, including experts from the Chinese Academy of Sciences, East China Normal University of Shanghai, University of Texas, Sapienza University of Rome and the University of Florence.

Using an innovative bioinformatics method, called FitCoal, the researchers examined the complete genomes of 3,154 current individuals from 50 different human populations and combined this data with palaeoenvironmental (climate) and palaeoanthropological (fossil) information that would allow them to trace back to prehistoric periods before the appearance of our species.

The results of the study have indeed revealed that between 930 and 813 thousand years ago, the population of our ancestors shrank by about 98.7 per cent to only about 1,300 fertile individuals - a number comparable to endangered species such as today's pandas.

This phenomenon, known as a genetic bottleneck, was most likely due to the drastic climatic changes characterising the so-called 'mid-Pleistocene transition'. Starting from a million years ago, glacial and interglacial cycles expanded planet-wide, leading to extreme arid conditions in Africa and the extinction of entire communities of large mammals. These adverse climatic and environmental conditions made survival extremely difficult even for our ancestors, bringing them to the brink of extinction. The event would have been as catastrophic as it was generative, probably giving rise to a species that is considered ancestral to the evolution of us Homo sapiens (which occurred around 200,000 years ago in Africa).

These genetic findings are confirmed by the absence of human fossils from that period. A gap of around 300,000 years that coincides almost perfectly with the period of demographic collapse detected by the study was indeed found. Before about a million years ago there is abundant palaeoanthropological evidence, but around 950,000 years ago this almost completely disappears from the entire African continent (as well as Eurasia), only to increase again around 650,000 years ago with finds that are usually attributed to the species Homo heidelbergensis.

"This period of demographic crisis", says Giorgio Manzi of Sapienza University, "may have played a fundamental role in human evolution. During a bottleneck, normal ecological and genetic balances are overturned, increasing the likelihood of unexpected genetic variants becoming fixed, contributing to the emergence of a new species"

"This new species is probably Homo heidelbergensis", stresses Fabio Di Vincenzo of the University of Florence, "which we can consider a true last common ancestor, i.e. the human form that spread from Africa into Eurasia, giving rise to the evolution of three different species: Homo sapiens in Africa, Neanderthals in Europe and Denisova in Asia".

References:

Genomic inference of a severe human bottleneck during the Early to Middle Pleistocene transition - Wangjie Hu, Ziqian Hao, Pengyuan Du, Fabio Di Vincenzo, Giorgio Manzi, Jialong Cui, Yun-Xin Fu, Yi-Hsuan Pan, Haipeng Li – Science(2023) https://doi.org/10.1101/2021.05.16.444351

Further Information

Giorgio Manzi
Department of Environmental Biology
giorgio.manzi@uniroma1.it