Nick Matzke has
compiled all the data on hominin cranial capacities into a single chart:
I think I can see a pattern there, can you? He also has data on body size and brain size over there, take a gander at it. It looks like a simple and obvious example of evolutionary change in our lineage, I think.
Alas, it only shows specimens older than 10,000 years. I’m sure that right around 6,000 years ago, there was a sudden, dramatic change as the deity injected a soul into those crania.
Do you mean to say that the crania of those that bought into the deity started getting smaller (a trend that seems to be continuing to this day)? Hmm, inject soul, take out brain. Makes sense.
I would be sorely disappointed in a deity that had to resort to such a mundane method as injection for an after market modification such as a soul. Maybe a soul is just attached with bolts? That would help explain why so many of us have removed ours, no need for hauling around all that excess weight.
I’m intrigued, and can’t see an explanation at the Panda’s Thumb post – is the apparent increase in the spread of data as we go left-to-right an effect of there being more examples of recent fossils, or does it indicate a real increase in variability going hand-in-hand with the increase in average capacity?
Yeah, sure, but look at all the gaps!
You don’t have fossil data for every day!
Which one of those dots is me?
Morgan, eyeballing the graph, it looks to me that there is no more variability on the right than on the left, on a percentage basis. Think about how much elephants vary in brain size. In absolute cc, likely much more than humans. I wouldn’t be surprised if a small and large elephant’s brain varied by more than 2000 cc, i.e., the entire volume of a large human brain. That doesn’t mean elephants have more variability in that measure. It just means they are bigger.
tommy: Funny you should mention that. Plato (a great inspiration to Christianity, I might add) talks about souls being rivited into bodies.
As for the graph and data, very interesting review. If only they could measure surface area of the cortex of these ancestors, which I suspect is a more interesting indicator of cognitive capacities.
Note that the average on the right-hand side is about 1500 cc, which is larger than the current average of 1400 cc. This obviously means that the pseudoscientific racists are right, and we’re getting progressively dumber because of all these pesky black people.
I would like a study of christian brains verses athiests brains. Still, christians manage to reproduce in abundance, despite their prediliction for little boys…..What genes are they preserving?
From the Panda’s Thumb article. “The evidence is simply an astonishing confirmation of evolution, and the endless pages of creationist diatribes about the lack of transitional hominid fossils are revealed to be mere verbal obfuscation when compared to this simple chart.”
When a chart like the one above is put into use the evidence becomes irrefutable. We need more like it.
According to the talk.origins article on hominid species there are at least eight different species in the interval that Nick examined.
http://www.talkorigins.org/faqs/homs/species.html
It’s not clear to me that the relationship he shows is referring to one particular lineage that he traces through all those species from Australopithecus to Homo sapiens or whether he’s lumping together all species throughout the timeframe from 3 million years go to the present.
It makes a big difference in how you interpret the data. In one case it looks like phyletic gradualism with a lot of variation, while in another case it might look punctuated. I think we should pause a bit before announcing that this is rock solid evidence of selection for increased brain size. It may well indicate such a thing (I think it does) but any competent creationist could raise very reasonable objections to the data.
For one thing, we need to know more about the correlation between body size and cranial capacity for each individual data point and each of the eight species. We would also like to know whether the data was from males or females and whether there was significant sexual dimorphism at the time.
We all know why these things are important. It’s because cranial capacity is correlated with body size and body size is correlated with environment as well as having a genetic component. Let’s imagine that primitive hominid species didn’t get enough food to live long lives and be healthy. As a result of poor living conditions their median body size was less than the maximum possible size they could have attained. Imagine that one of the new species (e.g., Homo erectus) migrated to a new environment where food was more plentiful and body sizes were larger. Another population branched off from Homo erectus in Africa and gave rise to Homo heidelbergensis and this new species was more advanced culturally and technologically so it was able to adapt better to a new environment and grow to larger size.
If we don’t know the relationship between sculls and the bodies they sat on top of, then we can’t decide between different senarios. The data is interesting and suggestive but not conclusive. There are too many obvious flaws and this should give us pause before heralding this as one of our icons of evolution.
On re-reading Nick’s article I can see that he relies on the conclusions of Henneberg and de Miguel (2004) who claim that “all hominins appear to be a single gradually evolving lineage” thus refuting the talk.origins article and most of the scientific literature on hominid species.
Perhaps this explains the difference between “hominid” and “hominin”? Are there any experts out there who can tell us if we need to revise all the textbooks? The Creationists are going to love this! It will be another example of stupid evolutionists who made up species where none existed. If true, it’s good evidence for anagenesis and that has serious implications for evolutionary theory.
Nick has a revised post up now, that color-codes the data points by species…and with that, you can now see signs of stasis in some species and more abrupt jumps between them.
Wonderful.
It might be educational and/or interesting to put in modern great apes such as the Chimpanzee species, other relatively intelligent current species (dolphins, dog, and of course octopus).
Also, the male/female issue is going to come up; female lower on average mean and median, with of course large overlap. Is “correcting” for body height or BMI or some other body size type correction any utility and validity?
Rivets are for chumps. All the good stuff is bonded with epoxy these days.
About 10 years ago Ian Tattersall published “The Fossil Trail” in which he makes several observations quite relevant to this chart.
1. These represent at least 3 different genera, and probably more.
2. Our progress on making an evolutionary tree for hominidae and its predecessors has been repeatedly stymied by scientists bringing in species-centric preconceptions that would not have happened with other groups of animals. Foremost among them: bigger brain = closer to us = more advanced.
3. Where’s H. Neanderthal?
Rivets are for chumps. …er, for *chimps*?
Anyway: a researcher who’s been doing cranial size and brain structure/function studies over hominid evolution since his 1997 dissertation on the topic:
Schoenemann, Tom — Anthropology, U.Michigan@Dearborn; U.Pennsylvania
His ‘papers’ page is current and links to many sources.
There are many other researchers of course.
Larry writes,
I think several of your points are reasonable — if it wasn’t clear before, I am agnostic on Henneberg & de Miguel’s idea that all fossil hominins are part of a “lineage”, depending on how you define “lineage” (is a sub-species an offshoot of a lineage or part of it? etc.). If you exclude the robust Australopithecines and the late Neandertals it might basically be true, but that is not something that has to be resolved before anything can be said about human evolution.
Dealing with some of your other points briefly: I have posted a version of the chart with the species colored in — and you will note that my first post included a chart from the paper that compared the changes in brain size *and* body size.
But surely you are letting details get in the way of the Big Picture here. The big picture is:
1. Evolution says that humans descended from apelike ancestors.
2. The available fossil evidence overwhelmingly confirms this hypothesis.
Since a large proportion of the public strongly disbelieves these facts, I would argue it is still important to get the basics out there. There would be a lot less public confusion and creationist exploitation if scientists would more regularly frame where their debates are placed relative to the Big Picture that they agree upon.
Male/female is one consideration; I would assume chronological age of the skull is as well. I know there are decent ways for inferring adult size based on a juvenile skull, but there still might be a little more play in some of the lesser-known species in that regard. Now all we need is for someone to superimpose the great chain of being for hominids along the x axis. :)
FWIW the points used for the graph exclude all juvenile specimens.
See, I am not sure that any of us should buy:
“But surely you are letting details get in the way of the Big Picture here. The big picture is:
1. Evolution says that humans descended from apelike ancestors.
2. The available fossil evidence overwhelmingly confirms this hypothesis.”
Getting the details right is important. The good guys have the harder job. We make good arguments, and do not necessarily convince anyone. But we make bad arguments, and they can pick us apart on little details.
The bad guys are not at all constrained by the truth or reasoning or any of that secular stuff.
Nick Matzke writes,
Of course I agree that evolution is overwhelmingly supported by the data. However, we need to be careful how we present that “overwhelming evidence.” If a non-expert like me can raise questions about the data on change in cranial capacity then so can a Creationist.
I don’t think being skeptical is an irrelevant “detail.” I think it’s part of good science and I think it’s an important part of what we should be doing to fight the opponents of science.
The chart created by Nick is the kind of thing I would show in an introductory anthropology course. it clearly shows one of the most important trends in hominid evolution. I just thought I’d address some of the questions raised in the comments:
First, hominin refers to the same group of animals for which hominid was traditionally used. Hominin has come out of cladistics and refers to Australopithecus, Paranthropus (if you choose to use it) and Homo. Other genera may be hominids/hominins, but at this time it is unclear what many of the very ancient animals really were. If a researcher refers to hominins, they will be using the term hominid to refer to the great apes or only the African apes depending.
Increasing variability in time….This could be attributed to the much, much larger sample sizes for later hominids or the larger (assumed) populations of such hominids, which would allow for greater variability (a flush effect) or several other possibilities.
As for female cranial size: whereas females do have smaller crania than males (on average), female crania are larger relative to body size than males. When examining the fossil record, determination of sex can be very tricky especially when there are no post-cranial remains.
Body size in the fossil record: Trying to relate body size and cranial capacity for the fossil record is incredibly difficult. There are precious few relatively complete specimens, (Lucy (A.L. 288) and Nariokotome Boy (WT15000) come to mind) making body size estimates unreliable at best. Further, there is no consensus on how many species are present and which specimens (including the mostly unassociated post-cranial remains) belong in which species. Ian Tatersall has argued that there may be twenty or more species represented in the time period covered by this chart.
Larry and others,
You seemed to be saying that a chart like this shouldn’t be used for public education because of the various questions about e.g. punctuations vs. smoothness. To me it sounds like you are basically saying that scientists shouldn’t show anything to the public until we understand every last thing. This seems like a ludicrous position to me, but maybe I’ve got you wrong.
I think it would be productive to discuss how educators and speakers *should* present the hominin fossil record to students and the public, if you don’t like the above graph. Would a graph like the above be appropriate with the species color in (as on PT?). Is the “constant rate of change” spin on the black-and-white graph primarily what you are objecting to, or is there something else?
Nick said:
That’s certainly not what I intended. The chart is neat. It should be shared. I do not think it provides evidence of what Nick called before “the big picture.”
I think it is easy to conflate evolution with our species’ evolution. A large brain wasn’t necessary. We put our imagined best features forward and call their development progress. We are stuck on ourselves.
(same reason, different science: fuss over Pluto. When we say “planet” what we really mean is “object like what we live on.” We are stuck on ourselves)
We have fossils from a number of related species, that seem to show an increas in cranial capacity over time. We have a few problems.
We do not believe that evolution towards larger cranial capacity is the natural order of things. It is in fact what happened with some of these species, but that was not the only option.
We do not believe that there was a constant, steady increase in cranial capacity. We do not believe evolution generally occurs in that way.
We do believe that the chart subsumes multiple speciation events, and we are not in full agreement about where they are.
And as neat as this big clean Nike swoosh of a chart is, we do not believe that an increase in the cranial capacity of any species not linearly ancestral to our own had any effect whatsoever on the size of our brains.
It’s a very interesting chart. I like the one with the color on Panda’s Thumb even better. But I would hope that we do not make a case for evolution based on it.
We think you’re a little full of yourself, there Jonathon
You silly vertebrates, with your fixation on the size of your brains–
It gives me pains.
It isn’t the size,
It’s what you do with it that determines whether they will call you “wise”.
The comparison of cranial capacities of all the hominins on that chart
Is not just worthwhile information–it is also art.
But, speaking as a cephalopod, I think it would be every bit as dumb
To look at cranial capacity as it would be to trace the history of your famed opposable thumb.
Why, look at the size of the cranium on Karl Rove–
And yet the man is as dumb as a kitchen appliance like a refrigerator or electric stove.
I’ll take tentacles over thumbs and a flexible nervous system over one stuffed into a skull, and if you don’t think that’s clever
Well, I never!
Ta-ta
Vertebrata!