海角大神

Fossil discovery complicates Homo sapiens' family tree

A team led by renowned paleoanthropologist Meave Leakey has discovered new fossils that they say suggests that our apelike ancestors shared their habitat with other hominid species. 

|
Fred Spoor/National Geographic/Nature/AP
This undated handout photo provided by National Geographic and Nature shows Meave Leakey as she carefully excavates the new face KNM-ER 62000 near Koobi Fora, northern Kenya. Leakey hails from a famous family of paleoanthropologists who say that the newly found fossils confirm their controversial theory that the human family tree may have sprouted some long-lost branches going back nearly two million years.

Our聽family聽tree聽may have聽sprouted聽some聽long-lost聽branches聽going聽back聽nearly聽2聽million聽years. A famous聽paleontology聽family聽has聽found聽fossils聽that they聽think聽confirm聽their聽theory聽that there are聽two聽additional聽pre-human聽species聽besides聽the聽one聽that聽eventually聽led聽to聽modern聽humans.

A team聽led聽by Meave Leakey, daughter-in-law of famed scientist Louis Leakey,聽found聽facial bones from聽one聽creature and jawbones from聽two聽others in Kenya. That聽led聽the researchers to conclude that man's early ancestor had plenty of human-like company from other聽species.

These would not be Homo erectus, believed to be our direct ancestor. They would be more like very distant cousins, who when you go聽back聽even longer in time, shared an ancient common ancestor,聽one聽scientist said.

But other experts in聽human聽evolution are not convinced by what they say is a leap to large conclusions based聽on聽limited evidence. It is the continuation of a long-running squabble in anthropology about the earliest members of our own genus, or class, called Homo 鈥攁n increasingly messy聽family聽history. And much of it stems from a controversial discovery that the Leakeys made 40聽years聽ago.

In their new findings, the Leakey team says that none of their newest聽fossil聽discoveries match erectus, so they had to be from another flat-faced relatively large聽species聽with big teeth.

The new specimens have "a really distinct profile" and thus they are "something very different," said Meave Leakey, describing the study published online Wednesday in Nature.

What these new bones did match was an old聽fossil聽that Meave and her husband Richard helped find in 1972 that was baffling. That skull, called 1470, just did not fit with Homo erectus, the Leakeys contended. They said it was too flat-faced with a non-jutting jaw. They initially said it was well more than 2.5聽million聽years聽old in a dating mistake that was later seized upon by creationists as evidence against evolution because it indicated how scientists can make dating mistakes. It turned out to be2聽million聽years聽old.

For the past 40聽years, the scientific question has been whether 1470 was a freak mutation of erectus or something new. For many聽years, the Leakeys have maintained that the male skull known as 1470 showed that there were more than聽one聽speciesof ancient hominids, but other scientists said it wasn't enough proof.

The Leakeys' new discoveries are more evidence that this earlier "enigmatic face" was a separate聽species, said study co-author Fred Spoor of the Max Planck Institute in Germany. The new bones were聽found聽between 2007 and 2009 about six miles (10 kilometers) away from the old site聽near聽the fossil-rich Lake Turkana region, Leakey said.

So that would make聽two聽species聽鈥 erectus and the聽one聽represented by 1470.

But it's not that simple. The Leakey scientific team contends that other聽fossils聽of old hominids 鈥 not those cited in their new study 鈥 don't seem to match either erectus or 1470. They argue that the other聽fossils聽seem to have smaller heads and not just because they are female. For that reason, the Leakeys believe there were three living Homo聽species聽between 1.8聽millionand聽2聽million聽years聽ago. They would be Homo erectus, the 1470聽species, and a third聽branch.

"Anyway you cut it there are three聽species," study co-author Susan Anton, an anthropologist at New York University. "One聽of them is named erectus and that ultimately in our opinion is going to lead to us."

Both of the聽species聽that Meave Leakey said existed聽back聽then went extinct more than a聽million聽years聽ago in evolutionary dead-ends.

"Human聽evolution is clearly not the straight line that it once was," Spoor said.

The three different聽species聽could have been living at the same time at the same place, but probably didn't interact much, he said. Still, he said, East Africa聽nearly聽2聽million聽years聽ago "was quite a crowded place."

And making matters somewhat more confusing, the Leakeys and Spoor refused to give names to the聽two聽non-erectus聽speciesor attach them to some of the other Homo聽species聽names that are in scientific literature but still disputed. That's because of confusion about what聽species聽belongs where, Anton said.

Two聽likely possibilities are Homo rudolfensis 鈥攚hich is where 1470 and its kin seem to belong 鈥 and Homo habilis, where the other non-erectus belong, Anton said. The team said the new聽fossils聽mean scientists can reclassify those categorized as non-erectus聽species聽and聽confirm聽the earlier but disputed Leakey claim.

But Tim White, a prominent evolutionary biologist at the University of California Berkeley, is not buying this new聽species聽idea, nor is Milford Wolpoff, a longtime professor of anthropology at the University of Michigan. They said the Leakeys are making too big a jump from too little evidence.

White said it's similar to someone looking at the jaw of a female gymnast in the Olympics, the jaw of a male shot-putter, ignoring the faces in the crowd and deciding the shot-putter and gymnast have to be a different聽species.

Eric Delson, a paleoanthropology professor at Lehman College in New York, said he buys the Leakeys' study, but added: "There's no question that it's not definite." He said it won't convince doubters until聽fossils聽of both sexes of both non- erectusspecies聽are聽found.

"It's a messy time period," Delson said.

___

!

You've read  of  free articles. Subscribe to continue.
Real news can be honest, hopeful, credible, constructive.
海角大神 was founded in 1908 to lift the standard of journalism and uplift humanity. We aim to 鈥渟peak the truth in love.鈥 Our goal is not to tell you what to think, but to give you the essential knowledge and understanding to come to your own intelligent conclusions. Join us in this mission by subscribing.
QR Code to Fossil discovery complicates Homo sapiens' family tree
Read this article in
/Science/2012/0808/Fossil-discovery-complicates-Homo-sapiens-family-tree
QR Code to Subscription page
Start your subscription today
/subscribe