African evolution

Article: Out of Africa, But Into What?

The "out of Africa" theory for human origins dominates modern science, beating out a competing theory that modern humans may have evolved in a few locations. But that does not mean the Africa-first theorists are sitting on their laurels.

Anthropologists and geneticists who study African origins are making the theory as robust as possible. They also are trying to answer a few contested questions: After Africa, where did early humans go first, and how does that explain the seeming anomaly that humans fossils at times suggest more than one origin?

This summer, two researchers at Cambridge University, the geneticist William Amos and biologist Andrea Manica, presented what they believe is a definitive answer: The evolution of skulls match up with previously found genetic evidence that pinpoint human origins to central or southern Africa before their rapid migration around the world.

The researchers analyzed the shapes of 4,666 male skulls from 105 places around the world, all of them less than 2,000 years old. As expected, they found that skulls nearer to Africa showed a higher degree of difference, reflecting the early evolutionary branching of modern humans. Human skulls found at great distances from Africa showed less change within their own groups, reflecting a loss of genetic diversity.

"What you find is a very nice linear decline of variability as you move farther away from Africa," Amos said. This pattern in the skulls also matched research in genetics showing more diversity in older African populations, and less at greater distances, the team reported in July in the journal Nature. "We failed to find evidence of a second origin," they said. Discoveries of skulls that suggest second origins are anomalies, since the preponderance of data show an out-of-Africa pattern.

Although the Cambridge team of skull experts confirmed their findings with previous genetic evidence, a debate has raged for a few decades on which is the best test of evolutionary branching: fossils or genetic samples from modern creatures?

The Cambridge researchers said the skulls often have the best advantage in the study of human origins. "There are so many of them and they come from populations that are not very well represented genetically," said Amos. Although genetic samples for aboriginal Americans and Australians are rare, for example, skulls are in abundance. The global skull data can "open up lots of nice testable hypotheses" on which routes early humans took when they left Africa, Amos said.

Many geneticists have argued that genetic samples are the best proof of migrations, and they are hard at work trying to trace human migrations as well. Since last year, the National Geographic Society in Washington, D.C., has led this research. "Every drop of human blood contains a history book written in the language of our genes," said Spencer Wells, a population geneticist. Wells is lead scientist in National Geographic's five-year project to analyze approximately 100,000 DNA samples from people across the globe.

Anthropologists and geneticists tend to agree that modern humans left Africa between 50,000 and 70,000 years ago, but a number of mysteries remain. Scientists are not sure which are the oldest populations in Africa, for example. They also wonder about the role a 5,000-mile network of trade routes called the Silk Road played in dispersing genetic diversity across the Middle East, India, and Asia. The number of times that humans migrated to the Americas is also up for debate, as is the time when they first arrived in the arctic regions.

Despite these mysteries, few experts doubt the out-of-Africa scenario in broad terms, said Erik Trinkaus, a physical anthropologist at Washington University in St. Louis. "The issue is how much modern humans spreading out of Africa after 50,000 years ago interbred with regional groups of archaic humans, where and when," he said. The new studies "reinforce the idea of a special isolation of modern humanity from anything less 'pure,'" meaning an avoidance of mating with other archaic humans.

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This work is so fascinating - I remember watching a National Geographic documentary titled "The Journey of Man" when I was in high school - unfortunately I don't remember much of it because I was really tired and fell asleep on the couch watching it. But just the idea that we all come from Africa.. it's really exciting.

And with evidence like this, I can't help but wonder how people don't believe in the concept of human evolution. Or perhaps we've got the wrong story, i.e. the Bible is more limited than we think. Maybe, because it wasn't until we developed as homo sapiens that we were able to read and write, our documentation of religion and God is missing the hundreds or thousands or millions of years when God also existed in the earlier humans' presence, when they didn't understand who He was, nor have any means of recording their experiences for future generations to comprehend.

Were Adam and Eve actually a pair of early, early humans, living in a lush Garden of Eden in Africa? Hmmm..!


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