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The period between 3 million and 2 million years ago was a transformative time in human history — it was back then that the genus Australopithecus led to the genus Homo, a new branch in the hominin family tree. But Australopithecus didn’t disappear the instant that Homo appeared in the fossil record. For a time, these two lineages lived together, sharing the landscape of northeastern Ethiopia.

On Valentine’s Day in 2018, a team of scientists walked across a flat expanse in the badlands of northeastern Ethiopia, scanning the ground for fossils. An eagle-eyed field assistant, Omar Abdulla, spotted an ancient molar lying on the surface, exposed by wind erosion.

Researchers have unearthed tooth fossils in Ethiopia dating to about 2.65 million years ago of a previously unknown species in the human evolutionary lineage, one that lived in the same time and place as the earliest-known member of the genus Homo to which our own species belongs.

Big History seeks to retell the human story in light of scientific advances by such methods as radiocarbon dating and genetic analysis. Brian Villmoare's book The Evolution of Everything: The Patterns and Causes of Big History provides a deep, causal view of the forces that have shaped the universe, the earth, and humanity.

Why recent study on modern brain size has experts scratching heads

Decades of research suggest that our brains have shrunk over time, but not all scientists agree.

Researchers refute a hypothesis that the human brain shrank 3,000 years ago as a result of the transition to living in modern societies.

No, we aren’t devolving: Human brain size hasn’t changed since Jebel Irhoud Person stalked the Sahara 300,000 years ago, says new team