Fossil Sparks: New Finds Ignite Controversy over Ape and Human Evolution
Bower, Bruce, Science News
Fifty years ago, British anatomist Wilfrid Le Gros Clark explained in a lecture why evolutionary scientists argue so vehemently about how ancient apelike and humanlike creatures eventually gave way to modern humans. "Every fossil relic which appears to throw light on connecting links in man's ancestry always has, and always will, arouse controversy," he stated, "and it is right that this should be so, for it is very true that the sparks of controversy often illuminate the way to truth."
Le Gros Clark was no stranger to wringing the truth out of bits of fossilized skeleton. In 1953, he assisted in unmasking the infamous Piltdown hoax. For more than 40 years, researchers had assumed that skull and jaw fragments collected from a British gravel pit came from a previously unknown early human species. The finds actually consisted of an orangutan's lower jaw and a modern man's skull.
But Le Gros Clark knew that genuine fossil discoveries ignite brighter sparks of controversy than any cranial con job ever could. Given limited evidence about long-gone populations of our predecessors, researchers devise competing evolutionary scenarios that are often difficult to disprove and that can easily accommodate whatever ancient bones turn up next.
Scientific reactions to the latest fossil finds and analyses underscore Le Gros Clark's point. Consider a handful of 10-million-year-old teeth recently unearthed in Ethiopia and attributed by their discoverers to a direct ancestor or close relative of the gorilla. If the scientists are right, ancient gorillas initially diverged from human ancestors more than 10 million years ago, several million years before DNA-based analyses date the split. However, some researchers regard the ancient teeth as remnants of an extinct ape that probably bore no relation at all to gorillas.
Further along evolution's path lie new fossil finds in Kenya that tell a disputed story about the emergence of direct human ancestors. Scientists who uncovered the ancient braincase and partial upper jaw say that this evidence, combined with prior fossils, indicates that two Homo species lived simultaneously in eastern Africa from about 1.9 million to 1.4 million years ago. In this scenario, one species died out and the other led to modern humans. But one prominent anthropologist rejects that conclusion, placing both new fossils in a single species that preceded Homo sapiens.
Finally, a research team recently argued that its new analysis of fossil teeth from sites in and beyond Africa supports the controversial notion that human ancestors trekked from Africa into Asia well before 2 million years ago and then colonized Europe from Asia. Critics of the work say that more fossil evidence is needed to overturn this team's conclusion that Africans migrated into Asia no more than 1.8 million years ago and eventually settled Europe as well.
"It's possible that hominids [the fossil ancestors of people] left Africa as early as 2 million years ago," says anthropologist Tim White of the University of California, Berkeley, "out it's hard to untangle the geographic patterns of their movements."
PIECES OF APE In February 2006, a field assistant working with fossil hunters in Ethiopia's Chorora Formation, a series of sediment layers dated at between 10 million and 11 million years old, found an ape's canine tooth. One year later, the researchers returned to the site and found eight more teeth from the same ancient-ape species, which they dubbed Chororapithecus abyssinicus.
Anthropologist Gen Suwa of the University of Tokyo and his coworkers see signs of gorilla ancestry in the fossils. Computerized tomography scans show that the gorilla-size teeth contain thick enamel suitable for shredding foods such as stems and leaves, the scientists report in the Aug. 23 Nature. Modern gorillas display slightly thinner dental enamel hut eat the same types of vegetation. …