Tuesday, May 23, 2017

Is Graecopithecus a hominin?

Graecopithecus, from Fuss and colleagues 2017, figure 1.

I've gotten a few questions about this Graecopithecus, so I guess I should weigh in with some kind of opinion.  The problem is that there isn't much to have an opinion on.

The Graecopithecus fossils in question are a jaw from Greece and a tooth from Bulgaria, shown above.  The fossils have been known for decades, but the new study from Jochen Fuss and colleagues applies micro-CT to the teeth and attempts to draw from that a classification of the fossil.  As far as I can tell (and remember I'm not a paleoanthropologist), this is a pretty neat way to get information out of a pretty uninformative fossil.  Based on the shape of the roots of the teeth, Fuss and colleagues propose that Graecopithecus may have been or definitely was a hominin.  Their certainty on this point varies in different locations in the paper, suggesting that reviewers made them tone it down.

As you can see in the photo above, the jaw is kind of a mess.  The teeth are extremely worn, so all the useful information that paleoanthropologists usually get from the crowns is gone.  The roots of the teeth are therefore the only information left for trying to figure out what sort of ape Graecopithecus was.  The authors claim that the roots of the fourth premolar are more similar to humans than to living great apes or apes known from the fossil record.  Ergo, it's a hominin.

As I mentioned above, in different parts of the paper, the authors' certainty regarding their hominin identification changes.  In the abstract, they say "it shows features that point to a possible phylogenetic affinity with hominins." Nicely cautious.  In the description of the specimens, they conclude, "G. freybergi is a hominid in the size range of female chimpanzees based on dentognathic size."  At the end of the paper, they conclude, "the dental root attributes of Graecopithecus suggest hominin affinities, such that its hominin status cannot be excluded."  Again, very cautious and appropriate.  The final sentence then goes back to being certain, "it seems likely that the Eastern Mediterranean needs to be considered as just as likely a place of hominine diversification and hominin origins as tropical Africa."

I'm not one to dismiss evidence simply because it originates from an evolutionist or it's inconvenient to my view of the world, but I am prone to be skeptical of evidence that is slim.  There's a lot that goes into being a hominin, based on the hominins that we know about.  The chief characteristic that currently unites all hominins is the ability to walk upright on two legs.  That involves a host of anatomical features that can be seen throughout the skeleton.  This is the root of a tooth.  I don't doubt that it's interesting and possibly very informative.  But is it informative enough to say that Graecopithecus is definitely a hominin?  Maybe.  Maybe not.

I'd love to see more micro-CT work done on other Miocene apes (and there are a lot of Miocene apes).  I'd like to know how different Graecopithecus really is from other Miocene apes.  I'd also really like to see more of the skeleton of Graecopithecus, because even if I grant that the shape of the tooth of Graecopithecus is only found in hominins, it's still possible that Graecopithecus is the one exception where that shape occurs in something that isn't a hominin.

My verdict: I'm no expert on hominin teeth, but call me a skeptic on this one.

Don't take my word for it, though. Read the original research report right here:

Fuss et al. 2017. Potential hominin affinities of Graecopithecus from the Late Miocene of Europe. PLoS ONE 12(5): e0177127.

Feedback? Email me at toddcharleswood [at] gmail [dot] com. If you enjoyed this article, please consider a contribution to Core Academy of Science. Thank you.

Monday, May 22, 2017

Origins 2017 Registration now open!

Registration is now available for Origins 2017, the annual conference of the Creation Biology Society and the Creation Geology Society.  The conference will be July 19-22 at San Diego Christian College.

Feedback? Email me at toddcharleswood [at] gmail [dot] com. If you enjoyed this article, please consider a contribution to Core Academy of Science. Thank you.

Monday, May 15, 2017

The Darrow Statue and the Friendly Atheist

Well, this was predictable.

I recently griped about the preposterously one-sided portrayal of Dayton in an article in the Chattanooga Times-Free Press. The article's author seems to go out of his way to find the most outrageous voice in the county to present as "opposition" to the statue of Clarence Darrow coming to the courthouse lawn. No voices from Rhea County were presented for balance or difference of opinion.  It's just the county vs. the humanists.  Our local TV station WRCB had a similar article, but they talked to the local Historical Society president Ralph Green for a different view.  They still portrayed this statue as "causing controversy," but I have to give them credit for at least talking to someone else in Rhea County.

I saw Ralph at a banquet last week, and I asked him about the article and the statue.  He told me there were a few people who were not really happy about the statue, but June Griffin is the only one making a fuss.  Again, my point here is that while Mrs. Griffin has every right to make a legal fuss about anything she wants, that does not make her a typical representative of Dayton or Rhea County.

And what do you know?  Someone else fell for this fake controversy.

On a blog titled the "Friendly Atheist," Hemant Mehta has a lot of fun with the article.  First, he recommends readers watch Inherit the Wind.  That might be an interesting movie, but it's terrible history.  Next, he describes Dayton as "one of those places where acceptance of evolution is still seen as heretical in many circles."  Ah yes, one of "those places."  I suppose that might be true in some circles I'm completely oblivious to, but I've been involved with teaching evolution in Rhea County for more than a decade now.  No one's tried to lynch me.

Next, we read, "But some activists are still not happy with the decision to allow the Darrow statue to go up."  Some activists?  He cites one.  After quoting the article, he's got one really great conclusion: "There’s your Christian reaction to the statue of Darrow: Evolution is a joke, this ain’t France, and we’re gonna vandalize that piece of art."

Christian reaction to the statue of Darrow?  Really?  One person in Rhea County is held up as the "Christian reaction?"  I'm sorry, but isn't that stereotyping?  At the very least, it doesn't exhibit basic principles of evidence-based reasoning or critical thinking.  A sample size of one is insufficient to represent the entire population of Christians.  It's not statistically significant.  Even more, Ralph Green is also quoted in the same article as being favorable to the statue, and he's a Christian too.

Here is where I should insert some kind of snide comment about atheists or even how terrible Mehta's blog is, but that would be falling victim to exactly what he's done to Dayton.  I don't want to be like that.  I want to do better than that.  I want to think carefully and critically and not just condemn entire groups of people for the behavior of a handful. I know I'm bad at this because it's human nature to jump to conclusions, so God help me!

Feedback? Email me at toddcharleswood [at] gmail [dot] com. If you enjoyed this article, please consider a contribution to Core Academy of Science. Thank you.

Friday, May 12, 2017

Bucking the Trend: The Brain and Date of Homo naledi

Based on a diagram from Wood (2016) (see below for full
reference).  Blue points represent Homo and red points
represent all other hominin genera.

There's a famous diagram going around that purportedly demonstrates continuous human evolution from nonhuman ancestors. It apparently was popularized by Nick Matzke back when the Panda's Thumb blog was still posting pretty regular content.  See his original post here.  In a followup on his website, he cautions that his data should be used wisely, or as he says, "don't be naive when you use the data."

Despite his reasonable warning, I've always felt that the diagram was misused in the zeal to refute creationists, primarily by ignoring phylogeny.  Despite some paleontologists' preference for the march-of-progress view of human evolution, the more realistic and biological view is one of a branching tree (or better, as Lee Berger describes it, a braided stream).  It seemed like too many people were using that diagram to emphasize a simplistic view of gradualistic emergence of modern humanity.  For example, the diagram includes the "robust australopithecines" that are now placed in a separate genus Paranthropus and are thought to be a side branch of human evolution.  It was as if otherwise sensible scientists were thinking, "Let's take a giant step backward in our understanding of evolution so we can score points against creationists."

So when I was putting together my response to Homo naledi last year, I decided to revisit the question (inspired at the time by reading RTB's latest human origins book).  You can read the technical details here:

Wood. 2016. Estimating the Statistical Significance of Hominin Encephalization. JCTSB 6:40-45.

In the paper, I concluded that there was definitely a trend, even when examined phylogenetically.  The closer you get to Homo sapiens (in radiometric time or on the phylogeny), the larger the average brain size gets.  The trend happens exclusively in Homo, though, which I thought was really interesting.  At the time I published that paper, the main exception was Homo floresiensis, the small hominin discovered in Indonesia.  He has a small brain size but lived relatively recently.  With the new dating result from Homo naledi, we can now add another point to that diagram, and you see that the trend is starting to get a little messy.  There are now two significant outliers from the main line of increasing brain size.

Don't read too much into that, though.  Two outliers aren't enough to negate a statistically significant trend, but they are intriguing.  And they make me wonder what else is out there just waiting to be discovered?

Feedback? Email me at toddcharleswood [at] gmail [dot] com. If you enjoyed this article, please consider a contribution to Core Academy of Science. Thank you.

Thursday, May 11, 2017

Homo naledi is not a mix of two different species

Composite skeleton of Homo naledi from the
Dinaledi Chamber.  Source: Wits

One of the odder reactions to Homo naledi when it was announced back in 2015 was the notion that there was more than one hominin species in the Dinaledi chamber.  I saw that idea hinted at in a Newsweek editorial from Jeffrey Schwartz, and it was later picked up by others including a few creationists.  The skeleton in that photo above is actually a composite probably made from multiple individuals.  How can we be sure that they all belong to the same species?  Now that we have fossils from the Lesedi chamber, let's revisit that claim.

I originally said it was incredibly unlikely to be more than one species for statistical reasons.  I posted this comment on a private group on Facebook, and I thought it might help explain why the "multiple species" idea doesn't work:
I think it has not been "dealt with" in any formal way, mostly because there is no merit to the claim since it's very unlikely. Actually, we might "calculate" a rough probability. Let's assume there are 30 individuals in the cave, evenly divided between two species. Marchi et al. (2016) report 14 right femoral elements recovered during the first two Dinaledi excavations, all of which are very similar to one another morphologically and therefore from a single species. But a random sample of 14 from a selection of 30 right femurs should give 7 of one species and 7 of the other, all things being equal. Given 30 right femurs, there are 30!/(14!)(16!) = 145422675 possible combinations of 14 different femurs. Since there are 15 right femurs from one species, that means there are 15 ways of selecting just 14 of those femurs. So that means there is a probability of 15/145422675 or 1e-7 of randomly selecting 14 right femurs from the same species (without replacement) in a sample of 30 right femurs evenly split between species. And that's just the right femurs! It gets impossibly improbable when you realize you have the same improbability for every other identifiable skeletal element. It's just a ludicrous proposal.
For those who don't like math (and there are many, don't feel bad), now we have another line of evidence that refutes with the "multiple species" idea: the skeleton of Neo.

Neo skeleton (Homo naledi) from Lesedi Chamber
Source: eLife
This skeleton was found in close proximity in the Lesedi chamber and very likely represents a single individual.  The skull possesses the diagnostic combination of characters of Homo naledi from the original Dinaledi chamber.  The collar bone matches the fragmentary ones recovered from the Dinaledi chamber.  The arm bones are less complete, but they also match the arm bones found in the Dinaledi chamber.  Neo's four hand bones are similar in shape to the hand recovered from the Dinaledi chamber, but they are larger.  The pieces of backbone from Lesedi also match the pieces of backbone from Dinaledi.  Neo's thigh bone (femur) is also very similar to the corresponding bones from the Dinaledi chamber.

So here we have the same set of characteristics observed from the composite skeleton of Dinaledi in a single individual's skeleton from Lesedi.  That really ought to clinch it: Homo naledi is one thing, not two different species stitched together.  The statistics support that conclusion, and so does the skeleton of Neo.

Let's put that idea to rest.

Feedback? Email me at toddcharleswood [at] gmail [dot] com. If you enjoyed this article, please consider a contribution to Core Academy of Science. Thank you.