The media frenzy last week over the new Australopithecus sediba papers coincided with all of my new
faculty events on campus. Whenever I was asked to introduce myself and to
describe what I teach and study, every response I heard had to do with the
recent reports of fossil hominin discoveries from Malapa, South Africa.
"I just read about some fossils on msNBC. So that's what
you're into?" … "How about those new finds! Wow!"
And although anything as equally well-preserved as the sediba stuff, but from 18 million years
earlier (like, say, new fossil primates from Rusinga Island) would be greeted
with relatively weak popping of eyeballs and with barely perceptible gaping of
jaws, I'm pleased to be so quickly matched to my field of study. I'm delighted
that paleoanthropology's so prominent in the media. Who doesn't want their
passion to be bathed in limelight? (Besides independent music fans.)
But why does paleoanthropology seem to garner
and even hog so much attention? This is a sometimes perplexing pattern in the science
news and here's a little back and forth between Ken and I inspired by this
question.
Ken: What, if anything, is this [the
new A. sediba finds and analyses]
really saying that we didn't already basically know?
Holly: We don’t know much about the time frame between
2.5 – 1.5 million years ago and this is when a lot of changes take place that
trend toward human-ness and away from ape-ness. The Malapa fossils (A. sediba)
preserve both cranial and postcranial bits of single individuals, so
proportions of brain size, body size, limbs, teeth, etc can be studied which,
again, is a rare opportunity for the hominin fossil record for this time period
which is comprised mainly of cranial and dental remains that even with a
well-preserved braincase for estimating brain size, don’t come with associated
postcranial or skeletal bits for putting that brain size in context. The Malapa
homs had small early hominin (read: ape) sized brains at a time in hominin
history when we hypothesize and even expect hominins to have relatively larger
brains. Many would also expect them to have larger brains given the modern
aspects of their hands and pelvis. Furthermore, the skeleton—from the hand to
the pelvis to the foot—shows a new mosaic of human-like, biped-like, homo-like,
australopith-like, and apelike traits. Lucy (A. afarensis) is famous for
showing a mosaic of these things but the Malapa finds show a different mix. These
finds are a window into the process of evolution, to the order of when traits
like we have appeared in the past. And even if it’s a tiny little momentary portal,
it’s still a peek!
Ken: Why is it
that a single new find can 'revolutionize' our understanding of 'what makes us
human' and all that BS? If we are so vulnerable to a single new find, then why
do we insist on making such bold claims about what we currently have?
Holly: I think
that some of it has to do with the colorful personalities of the people who are
drawn to paleoanthropology—the scientists, writers, reporters, critics, fans
etc. If you care so much about your fossil relatives, that’s pretty
narcissistic isn’t it? I’m not sure new finds revolutionize anybody’s understanding
of “what makes them human” unless they’re
new to paleoanthropology. First-timers to the fossil evidence are probably
blown away and their world-views are changed, but long-time fans would probably
describe their new perspective as hypothesis creation or story change. And yes,
new finds do re-write the story of human evolution if your story includes
details beyond “We share a common ancestor with chimpanzees about 6 million
years ago and since then bipedalism and big brains evolved.” But even that
story could be re-written if we find fossil evidence that bipedalism preceded
the LCA (last common ancestor) with chimpanzees.
Why do we “make
such bold claims about what we currently have?” I don’t think paleoanthropology
holds the monopoly on this behavior. As we discuss on the MT quite a bit, this
is part of the game of science and academia, of getting tenure and promotion,
of getting grant money.
I also think
that paleoanthropologists are simply excited about their finds and can’t help
but share that with the rest of us. If that excitement draws science-deniers
closer to the light, then that’s a huge bonus.
I think there are only so many ways to make sausage. I'm pretty sure that's not the right idiom, but I'm trying to say
that there are only so many ways to garner interest for news reports on new
fossil hominins... so they all start to sound the same. Unless you read further
and learn the ins and outs of paleoanthropology, then each new fossil is
interesting in that informed context, from that informed perspective. If you do
a search, all the phrases are the same for fossil news but if you search for
reports on raging fires you find just as much repetition/unoriginality. There
are only so many words and phrases at our disposal.
Ken: Beyond the circus atmosphere of each successive 'revolutionary' claim, what do we
basically know about our origins that seems solid?
Holly: Humans share
a common ancestor with chimpanzees between 8-4 million years ago (mya). It
lived in Africa. It may or may not have been bipedal but the evidence right now
indicates it was not. Since that split, for four million years (until about 2
mya), hominin evolution took place exclusively in Africa (the record is largest
from East and South Africa), during which time body size remained fairly small (with
rare exceptions) and human-style bipedal traits accumulate in the skeleton.
Teeth are rather large during that time, but they trend smaller as time passes,
especially the canine. About 3.5 mya a separate lineage splits from the australopiths
and the lineage that ends in us. It’s the robust australopiths who had large
teeth and jaws used for a harder and/or tougher diet than contemporaneous
hominins. The robusts lived only in Africa and disappear around 1 mya. The
first cut marked bone and stone tools show up around 2.5 mya in Ethiopia signalling
a change in hominin behavior/ecology/diet. As we discussed here, some much
earlier cut-marked bones were found at another Ethiopian site 0.8 mya earlier. These
isolated “firsts” are followed by a much more regular and ever-denser record of
tool production and meat-processing after 2 mya. Just after 2 mya we find the
first hominin fossils outside of Africa—in Georgia and Indonesia. The brain
gets slightly larger, but not by much, at this time and the skeleton, by about
1.5 mya is close to ours except for the brain size (which is still about half-three-quarters
of our size), tooth size (still a bit large), and the shoulder anatomy which
doesn’t seem to have the full range of motion of ours (which would mean
throwing wasn’t “modern”). Since the first stone tools appear, there is a fairly
steady increase in technological complexity to the present, although the
Acheulean “handaxe” industry certainly sustains for quite a while (perhaps a
million years) suggesting that big bulky stone bifaces were a lot more useful
than they appear. Alongside the technological development is ever-increasing
body size, with variation present, but the maximum size increases over time.
There is also ever-increasing brain size to the present. And this is all
happening as we find hominins inhabiting distant and diverse landscapes.*
Ken: Or is this [
A. sediba] basically just another specimen, even if it's interesting?
Holly: Nope. It’s not just another specimen. We don’t
have many skeletons let alone skeletons with cranial remains and teeth
associated with them. Let alone more than one skeleton associated, giving us
some idea of variation within a species, or at least a family. These fossils are
truly extraordinary and deserve all the fanfare.
Do all new hominin fossils
deserve so much fanfare? I'm sure answers vary widely person-to-person. Some of
us hyperventilate over half a molar, others could never hear of a fossil their
whole life and die incredibly happy. I don't go ga-ga when stock prices go up,
I don't swoon when I read headlines that Brad dumped Angelina, I don't drop
everything when Marc Jacobs makes new pants, but all reports of those stories
certainly come off as obnoxious as those about new hominin fossils. It's just
show biz. And I'm fine with show biz if it gets people interested in evolution
which can snowball into them learning about evolution. I love that new fossils
even make the news when there are stocks, and celebs, and fashion shows hogging
so much of the attention.
*I left out so many established/cool details because this post is already too long.
