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A Brief History of Human Evolution and an Ancient Bottleneck

Humans and chimpanzees share a common ancestor from over 6 million years ago. The genus Homo emerged around 2.8 million years ago in East Africa with species like Homo habilis and later Homo erectus, who spread into Eurasia and developed more advanced tools.

Around 600,000 years ago, Homo heidelbergensis appeared, some of whom evolved into Neanderthals in Europe and modern Homo sapiens in Africa by about 300,000 years ago. Fossils from Morocco (Jebel Irhoud) mark some of the earliest Homo sapiens remains.

Recent DNA analysis of modern humans suggests a dramatic population bottleneck occurred between 930,000 and 813,000 years ago, reducing the human population to about 1,280 individuals for over 100,000 years. This likely resulted from severe climate changes during the Early to Middle Pleistocene Transition, including intense glaciations, droughts, and ecological shifts in Africa.

The bottleneck led to a major loss of genetic diversity and may explain the scarcity of fossils from this period. After it ended, human populations grew rapidly, possibly aided by better climate and the use of fire.

However, some scientists challenge the bottleneck theory, arguing that non-African DNA doesn't show signs of it. Newer studies suggest human ancestry includes at least two ancient populations (Lineages A and B) that split around 1.5 million years ago and merged again about 300,000 years ago. Lineage A experienced a bottleneck, while B contributed a smaller but significant portion of modern human DNA.

This complex picture reshapes our understanding of human origins, highlighting the role of climate, population mixing, and genetic change in our evolution.