We humans are a strange bunch. We have self-awareness and yet often act on impulses that remain hidden. We were forged in adversity but live in a world of plenty. Who are we? What is to become of us? To these age-old questions, science has in recent years brought powerful tools and reams of data.
We know, for instance, that three million years ago, a group of primates known as the australopithecines was walking capably on two legs—the better to navigate the African savanna—and yet still had long arms suited to life in the trees. In searching for clues to what selective pressures drove this transition, paleontologists discovered a 3.3-million-year-old fossil—“Lucy's baby”—confirming that the famous Australopithecus afarensis skeleton “Lucy” indeed contains a mosaic of traits related to both walking and climbing (page 4). Other paleontologists have uncovered remains of a previously unknown human species in South Africa (page 12).
Once we came down out of the trees, we lost our hair. Why? It may sound like a dumb question from the back of the classroom, but scientists have asked it and found that a lack of body hair was essential for keeping our primeval bodies cool (page 22).
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Genetics opens a big window onto our human ancestry. If we share nearly 99 percent of our DNA with chimps, why are we, not them, living in the suburbs and driving cars? How does a small amount of DNA make such a big difference? To find out, biostatistician Katherine S. Pollard and others are figuring out what that 1 percent of DNA is and what it does—her account is in this issue (page 30). We also look at how scientists are studying the minuscule bits of DNA that differ from one individual to another for clues to our origins and evolution (page 60).
Human evolution and culture are often intertwined. For instance, as humans started to live longer, grandparents played a role in family life, which in turn made possible more complex social behaviors (page 38).
The more we learn about our own evolution, the more complicated the story becomes. New findings have pushed back the date at which hunter-gatherers colonized the Americas (page 68). And the discovery of “hobbits”—a human species of small stature—has turned the science of human origins on its ear (page 84).
Where is evolution taking us? We present two points of view. Jonathan K. Pritchard, professor of human genetics at the University of Chicago, argues that selection pressure typically acts over tens of thousands of years (page 98), which means we probably won't evolve much anytime soon. But stasis is only one possible future, says University of Washington astrobiologist Peter Ward. In adapting to new environments—say, a colony on Mars—our human species may eventually diverge into two or more. Or we could go the cyborg route and merge with machines (page 106). Whichever option you prefer, there is plenty to ponder.