Kenyan Fossils Rekindle Debate Over Early Human Diversity
By Kate Wong
Scientific American Blogs
August 9, 2012 
http://blogs.scientificamerican.com/observations/2012/08/09/kenyan-fossils-rekindle-debate-over-early-human-diversity/

[moderator: please use the link above to view the
accompanying illustrations]

If I had to pick the hottest topic in paleoanthropology
right now, I'd say it's the origin and early evolution
of our genus, Homo. Researchers know quite a bit about
our australopithecine predecessors (Lucy and her ilk)
and about later phases of Homo's evolution. But the dawn
of our lineage is cloaked in mystery. One question
experts have long puzzled over is whether Homo split
into multiple lineages early on, or whether the known
early Homo fossils all belong to a single lineage. To
that end, new discoveries made at the site of Koobi Fora
in northern Kenya-one of the Leakey's longtime fossil
hunting grounds-are said to settle that matter in favor
of multiple lineages. But some critics disagree.

The new finds-a partial face including almost all of the
molars in the upper jaw, a nearly complete lower jaw and
a partial lower jaw that date to between 1.78 million
and 1.95 million years ago-bear on the identity of a
famously enigmatic skull from Koobi Fora known as KNM-ER
1470. Ever since the discovery of the 1470 skull in
1972, researchers have struggled to place it in the
human family tree. On one hand, at nearly two million
years old it is the same age as H. habilis fossils from
Koobi Fora and other locales in East Africa. The skull
also shares some features in common with that species,
which most researchers consider to be the founding
member of Homo. On the other hand, 1470 is much larger
than established H. habilis fossils, and differs from
them in having a flat, long face, among other
distinctive traits. Some experts thus assigned 1470 and
some other fossils from Koobi Fora to a separate
species, H. rudolfensis. 

But nailing down whether 1470 is a rogue H. habilis or a
separate species has been tricky because no other skull
shared that long, flat face and the specimen lacks teeth
and a lower jaw to compare with other fossils. This is
where the new fossils from Koobi Fora come in. In a
paper published in the August 9 Nature, Meave Leakey of
the Turkana Basin Institute in Nairobi, Fred Spoor of
the Max Planck Institute for Evolutionary Anthropology
in Leipzig and their colleagues report that the new face
mirrors 1470's face shape, although it is smaller
overall. Inferring 1470's upper jaw anatomy from the new
face, the authors say the lower jaw fossils they found
are good matches for the upper jaws of 1470 and the new
face. (Scientific American is part of Nature Publishing
Group.) New mandible from Koobi Fora

"For the past 40 years we have looked long and hard in
the vast expanse of sediments around Lake Turkana for
fossils that confirm the unique features of 1470's face
and show us what its teeth and lower jaw would have
looked like," Leakey remarked in a prepared statement.
"At last we have some answers." The answers, in their
view, indicate that 1470 and the new fossils represent a
distinct human lineage from other early Homo fossils.
This would mean that two Homo lineages lived alongside
our ancestor H. erectus. H. erectus itself may have
evolved from one of these two groups or another, as-yet-
unknown group. The researchers did not formally name the
new fossils from Koobi Fora, because of confusion
surrounding the fossil that defines H. habilis, but they
suggest that it may be appropriate to assign them to H.
rudolfensis. Bottom line, they're saying the fossils
confirm that the non-erectus early Homo fossils in East
Africa constitute two lineages, not one.

Although it may be hard to imagine sharing turf with
another human species today, members of these ancient
contemporaneous lineages need not have stepped on each
other's toes. In background materials distributed to the
press the discovery team noted that chimpanzees and
gorillas live in some of the same habitats. Both eat
ripe fruit, but gorillas focus more heavily on tough
vegetation than chimps do. "The early hominins [members
of the human branch of the family tree] could have
separated their neighborhoods in the same way," the
researchers explain. "They may simply have focused on
different primary food items." Exactly what these
hominins were eating is uncertain, "but there are clues
from the arrangement of the face and jaws that the newly
described fossils, and the previously known [1470
skull], with their tall faces but shortened front tooth
row, may have been focusing on foods that required
chewing on the back teeth." Analyses of the chemical
composition of the teeth, as well as their wear marks,
may yield further insights into what these hominins ate.

In an accompanying commentary Bernard Wood of George
Washington University calls the new evidence for at
least two parallel lineages in the early evolution of
Homo "compelling." Indeed he suggests that this chapter
of our evolutionary history was even more complex than
that. "My prediction is that by 2064, 100 years after
[Louis] Leakey and colleagues' description of H.
habilis, researchers will view our current hypotheses
about this phase of human evolution as remarkably
simplistic," he writes.

Other researchers are not convinced that the new Koobi
Fora fossils show multiple lineages of early Homo co-
existed. Adam Van Arsdale of Wellesly College, who has
studied the 1.76 million-year-old H. erectus fossils
from the site of Dmanisi in the Republic of Georgia,
notes that in light of the considerable variation
evident in the well-dated Dmanisi sample, the variation
in the early Homo fossils from Africa can be
accommodated by one species. In fact, the new Kenyan
fossils show features in common with the Dmanisi ones,
and thus help to link early Homo in Africa to H. erectus
in Georgia, he says. In his view, all of these fossils-
the habilis/rufolfensis ones and H. erectus-belong to
one lineage.

"What the African assemblage lacks is a good sample from
a single locality that shows variation. Instead you have
lots of fragmentary, isolated specimens, all with
temporal uncertainty, that show a huge amount of
variation," Van Arsdale explains. Whereas Leakey and
Spoor see this variation as evidence for multiple
concurrent lineages, "I tend to see this new evidence as
making it harder to reject the idea of a single evolving
lineage," he says.

A more pointed criticism of the new study comes from Lee
Berger of the University of the Witwatersrand in
Johannesburg. Berger notes that in their paper Leakey,
Spoor and their colleagues neglected to compare the new
Koobi Fora fossils to Australopithecus africanus and A.
sediba fossils from South Africa, which were
contemporaries of early Homo from East Africa. (Berger
led the team that discovered A. sediba, which was
announced in 2010 and held up as a possible ancestor of
Homo.) By ignoring those South African fossils, Berger
contends, the team cannot rule out alternatives to their
interpretation.

Berger also took issue with the team's use of
fragmentary material to argue its position. "All this
paper does, unfortunately, is highlight the mess that
the isolated and fragmentary East African record in this
time period makes of the debate around the origins of
the genus Homo, and it does little to illuminate the
question," he contends. Berger has previously argued
that A. sediba, which is best known from two largely
complete skeletons exhibiting a mosaic of
australopithecine-like and Homo-like traits,
demonstrates that evolution mixed and matched fossil
human features in sometimes surprising ways, and that
fragmentary remains therefore cannot be reliably
assigned to species. "We and others have shown that you
can't take isolated bits and force them into anatomical
association.  The [Koobi Fora] mandible goes with the
maxilla?  Where is the evidence for that," he demands.
"While we need more fossils like this, it's not helpful
to shoehorn them into debates they are not complete
enough to be of use as evidence in."

Spoor counters that he and his colleagues did include
the South African fossils in their analysis, but that
they excluded those comparisons from their report
because their Nature paper focuses on the question of
what the new fossils reveal about taxa of early Homo in
eastern Africa. "A. africanus and sediba have nothing to
say about that," he asserts, noting that africanus and
sediba have primitive faces, with "nothing specifically
Homo-like in the skull." He adds, "the interesting parts
of A. sediba are in the postcranial skeleton."

Suffice it to say, I doubt very much that we have heard
the last of this debate. Stay tuned.

Update (8/9/12 at 9:53 A.M.): Paleoanthropologist Philip
G. Rightmire of Harvard University sent the below
observations about the new fossils. Like Van Arsdale,
Rightmire has long studied the Dmanisi fossils, but he
arrives at different conclusion about the Koobi Fora
remains:

"It's my impression that the authors are on the money in
attributing their material to the hypodigm including
KNM-ER 1470. For a long time, this group was quite
poorly documented and therefore enigmatic. The new
facial parts duplicate some of the key features of the
original (very distinctive) face, but at a much smaller
scale. Sex dimorphism and individual variation within a
single lineage seems to be the best explanation. Also,
it's clear that this lineage differs from specimens such
as OH 13, OH 24, and KNM-ER 1813 (attributed to Homo
habilis). I'd say that there is a good case for the
presence of two distinct Homo lineages along side Homo
erectus. For me, an important question is which (if any)
of these hominins took the first steps out of Africa, to
establish settlements at localities such as Dmanisi. Our
material is best described as early Homo erectus, but I
think that the direct ancestors to the Dmanisi
population were a more archaic form of Homo. The first
hominins out of Africa may have been Homo habilis (not
the group documented in the new paper). Or we may have
to keep looking for an appropriate ancestor to Homo
erectus. In any case, Homo erectus evolving in Asia
probably dispersed only later (back) to Africa, and of
course toward the Far East."

___________________________________________

Portside aims to provide material of interest to people
on the left that will help them to interpret the world
and to change it.

Submit via email: [log in to unmask]

Submit via the Web: http://portside.org/submittous3

Frequently asked questions: http://portside.org/faq

Sub/Unsub: http://portside.org/subscribe-and-unsubscribe

Search Portside archives: http://portside.org/archive

Contribute to Portside: https://portside.org/donate