We’ve always thought that humans evolved from a straightforward line of ancestors. But new research from the University of Cambridge shows things are more complicated. It turns out our family tree has some twists.
Researchers discovered that about 1.5 million years ago, human populations split into two. Then, around 300,000 years ago, they came back together. Surprisingly, one of these separated groups has made a more significant mark on our DNA than the other.
Geneticist Trevor Cousins, who led the study, says, "The question of where we come from fascinates us. It’s a complex history." Traditionally, evolution has been depicted as a branching tree, where each split represents a point when species could no longer breed with each other.
However, the story of our evolution is more like a winding road. There were times when groups separated, blended back together, and then diverged again. This back-and-forth makes it tricky to define exact species boundaries.
Cousins notes that interbreeding and genetic exchanges have likely fueled the emergence of new species throughout time. In our case, we’ve mixed with Neanderthals and Denisovans, showing that our evolutionary path hasn’t been straightforward.
The team used advanced statistical models alongside DNA data from the 1000 Genomes Project and the Human Genome Diversity Project. Their analysis revealed that one ancestral group shrank significantly before slowly growing again over a million years. This population would later contribute around 80% of modern human genetic material.
Interestingly, Neanderthal genes are found only in non-African modern humans, making up about 2% of their DNA. When these two groups mixed 300,000 years ago, only about 20% of modern human genes came from the smaller population. Yet, some genes from that minority group—especially those related to brain function—may have played a crucial role in our evolution.
As researcher Aylwyn Scally pointed out, "Immediately after the split, one population faced a severe bottleneck, suggesting it shrank to a very small size."
This study revolutionizes our understanding of evolution. It suggests that the human lineage is more tangled than we’ve realized. Instead of clear-cut lines, it’s a rich web of connections.
With more advancements in genetic research, we might unlock even more chapters of our evolutionary history. The complexities of our past remind us that evolution is an intricate dance, filled with surprises and connections yet to be discovered.
For more on the details of this research, check out the study published in Nature Genetics.
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