THE HUMAN EVOLUTION TREE GETS BUSHIER

The next two wire stories make a nice juxtaposition: yet another fossil
hominid that shows the tree of human evolution is even bushier than we
thought; and a move by Arkansas legislators to prohibit the teaching of
evolution. It's hard to believe but here it is: 2001 with an embarrassment
of fossil riches and creationists bleeting for "just one fossil." I suppose
the good book was right: there are none so blind as those who will not see.

Reuters
Paleontologists in Africa have found the 3.5 million-year-old skull from
what they say is an entirely new branch of the early human family tree.

Paleontologists in Africa have found a 3.5 million-year-old skull from
what they say is an entirely new branch of the early human family tree,
a discovery that threatens to overturn the prevailing view that a single
line of descent stretched through the early stages of human ancestry.

The discoverers and other scientists of human evolution say they are not
necessarily surprised by the findings, but certainly confused.

Now it seems that the fossil species Australopithecus afarensis, which
lived from about four million to three million years ago and is best
known from the celebrated Lucy skeleton, was not alone on the African
plain. Lucy may not even be a direct human ancestor after all.

Indeed, the family tree, once drawn with a trunk straight and true, is
beginning to look more like a bush, with a tangle of branches of
uncertain relationship leading in many directions.

The skull discovery was made in 1999 by a research team led by Dr. Meave
G. Leakey excavating on the western side of Lake Turkana in northern
Kenya.

Only after careful analysis did the scientists conclude that the nearly
complete skull and partial jaw represented a completely different genus
and species. The flattened face and small molars were strikingly
different from those of the contemporary afarensis, or Lucy, species.

In a report in today's issue of the journal Nature, Dr. Leakey formally
named the new member of the hominid family Kenyanthropus platyops, or
flat-faced man of Kenya. The dates for the fossils, ranging from 3.2 to
3.5 million years old, were derived from volcanic ash buried at the
site. The sex of the individual has not been determined.

"Kenyanthropus shows persuasively that at least two lineages existed as
far back as 3.5 million years," Dr. Leakey said in a statement issued by
the National Museums of Kenya in Nairobi, where she is the principal
paleoanthropologist. "The early stages of human evolution are more
complex than we previously thought."

In a telephone interview, Dr. Leakey said the diversity in fossil
hominids should not be surprising, because the ancestry of mammals is
usually marked by many different branches. When the early hominids split
off from ancestors of the ape and started walking on two legs, they
would have been capable of moving into new habitats and developing into
new species.

Dr. Ian Tattersall, an evolutionary biologist at the American Museum of
Natural History in New York, said the discovery was "very important
because it finally recognized the diversity among fossil hominids."

Until recently, scientists have recognized only three groups of
hominids. The genus Homo evolved more than two million years ago and led
to modern humans. Paranthropus was a robust contemporary of Homo that
became extinct about one million years ago. Both groups were presumed to
have descended from an early species of the other hominid genus,
Australopithecus.

Ever since its discovery in 1974 in Ethiopia by Dr. Donald Johanson, the
australopithecine known as Lucy, or afarensis, has been generally
regarded as the most likely common ancestor of all subsequent hominids,
including humans.

In the absence of any other hominid fossils between about 3.8 million
and 3 million years ago, it seemed to be the only tentative conclusion
scientists could draw.

Dr. Frank Brown, a University of Utah geologist who was a member of Dr.
Leakey's team, said the place of afarensis and the new fossil species in
human ancestry would be debated in the coming years. Dr. Leakey's
journal article does not take a position on the issue.

"Anthropologists will have to decide which of these forms of early human
actually lies in our ancestral tree," Dr. Brown said. "It cannot be
both."

In a commentary in Nature, Dr. Daniel E. Lieberman of George Washington
University wrote, "I suspect the chief role of K. platyops in the next
few years will be to act as a sort of party spoiler, highlighting the
confusion that confronts research into evolutionary relationships among
hominids."

Or as Dr. Tim D. White of the University of California at Berkeley said
in an interview, "The arms will be waving faster than helicopter
blades."

Dr. White is a paleoanthropologist working in Ethiopia who was earlier
associated with Dr. Johanson in research on the Lucy specimen. He
reserved judgment on the new discovery, saying that whether the "new
fossils expand an envelope beyond a single lineage or fit within the old
envelope of afarensis" was still an open question.

Meave Leakey is the wife of Richard Leakey, himself a paleontologist and
the son of Louis and Mary Leakey, who pioneered the search for early
hominid fossils in Africa. One of Meave Leakey's co-authors is her
daughter, Louise, who is completing doctoral studies at the University
of London and carrying on the family's fossil-hunting tradition.

If the issue becomes an Australopithecus afarensis vs. Kenyanthropus
platyops debate, it could reopen old wounds from previous conflicts
between the Leakey family and Dr. Johanson, which became bitter after
the Lucy discovery. Among other issues, members of the Leakey family
initially questioned the place of afarensis in early human evolution.

In a foretaste of arguments to come, Dr. Lieberman said the newly
discovered skull "almost certainly" represents a new species. None of
its main characteristics is in itself new, he noted, but "the
combination of features is not found in any other known species." But he
said he was less sure that the fossils belonged to a new genus, a
broader grouping.

Dr. Leakey acknowledged that "the genus designation is going to be what
people question most."

Defending her decision, she said that the fossils definitely did not
resemble the genus Homo, which evolved much later, and that the teeth
were too small and the face too distinctive to belong to a member of the
Paranthropus genus. And she said she resisted placing the species within
the Australopithecus genus simply because they were contemporaries.

"Australopithecus has become too much of a dumping place," Dr. Leakey
complained.

In particular, she said in the team's report that the fossils' "unique
pattern of facial and dental morphology" probably reflected the fact
that the species occupied a new habitat and ate different foods than the
afarensis.

From about 2.5 million years onward, until the extinction of
Neanderthals about 28,000 years ago, there were always two or more
species of hominid in existence.

For two decades, afarensis stood alone as the earliest hominid species.
Then Dr. White in 1994 discovered fossils in Ethiopia that are thought
to be 4.4 million years old and have been named Ardipithecus ramidus;
details of the fossils remain scant. A year later, Dr. Leakey identified
the earliest known australopithecine, the four-million-year-old
anamensis.

The new discovery, Dr. Leakey said, "just shows that the hominid
diversity that was apparent from 2.5 million years on is now extended
much earlier."
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E-SKEPTIC FOR MARCH 28, 2001 Copyright 2001 Michael Shermer, Skeptics
Society, Skeptic magazine, e-Skeptic magazine (www.skeptic.com and skepticmag@aol.com).

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