Modern humans are evolutionary survivors , thriving generation after generation while our ancient relatives died out. Now, new research into our brain chemistry suggests that an enzyme unique to Homo sapiens may have made us more efficient water seekers than our closest extinct relatives.

About 600,000 years ago, modern humans genetically diverged from the lineage that produced Neanderthals and Denisovans — our closest cousins in the family tree of human species. At some point after the split, an enzyme called adenylosuccinate lyase, or ADSL, evolved to be different in Homo sapiens. In the enzyme’s chain of 484 amino acids, one amino acid at position 429, called alanine, was replaced with valine. It’s a small change, but it produced a version of ADSL that only modern humans possess.

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