Oxford neurobiologist Colin Blakemore, a distinguished researcher and author of several popular-science books, gave the Ferrier Prize Lecture at the Royal Society on March 15 and was just interviewed by The Guardian. His topic: the evolution of the human brain. Although the lecture precis implies that Blakemore talked about several topics, the Guardian singled out one: Blakemore’s apparent assertion that a rapid increase in human brain size a few hundred thousand years ago was due to a “macromutation”—a single change in the DNA of large effect:
In a recent lecture, the Oxford neurobiologist argued that a mutation in the brain of a single human being 200,000 years ago turned intellectually able apemen into a super-intelligent species that would conquer the world. In short, Homo sapiens is a genetic accident.
Blakemore asks:
The question is: why is [our brain] so big compared to the brains of our predecessors, such as Homo erectus? Until 200,000 years ago, there had been a gradual increase in brain size among hominins, starting three million years ago. Then, abruptly, there was a remarkable increase of about 30% or so.
Blakemore suggests that this big mutation might have occurred in “mitochondrial Eve,” the woman from whom, he says, we all descend:
Genetic studies suggest every living human can be traced back to a single woman called “Mitochondrial Eve” who lived about 200,000 years ago. My suggestion is that the sudden expansion of the brain 200,000 years ago was a dramatic spontaneous mutation in the brain of Mitochondrial Eve or a relative which then spread through the species. A change in a single gene would have been enough.
Finally, Blakemore suggests that the spread of this mutation through our ancestors, and its fixation, was not due to natural selection!:
How have scientists explained this jump in brain size?
Many have argued that if there was a dramatic increase in brain size, there must have been a fantastic advantage that came with it: improvements in tool construction, more complex language and other cultural changes. In other words, they say simple natural selection explains what happened.
So what is your take on this view?
I think they’re fooling themselves. There was very little change in human behaviour at this time, as far as we can see from the fossil record – certainly not one that is explained by a sudden jump in the size of the human brain. These hand-waving arguments about tiny changes in culture explaining the emergence of such a huge change in brain structure just doesn’t hold water. It’s like arguing that a reptile suddenly developed fully formed wings and then sat around for 200,000 years before suddenly saying: Oh my God, I’ve discovered I can fly. It’s ridiculous. . .
What effect did this have?
Very little at first. The environment of early humans was so clement and rich in resources that this greedy new brain, which would have absorbed even more of the body’s energy, could be sustained without danger. Later, when times got hard, during droughts or climate changes, it helped us deal with these crises, which could otherwise have killed us off, by dreaming up novel ideas to problems.
Okay, here are just some of the problems with Blakemore’s thesis:
1. First of all—and this has been endlessly repeated by geneticists—it’s misleading to say that “every living human can be traced back to a single woman called ‘Mitochondrial Eve’ who lived about 200,000 years ago.” What we know is that all the DNA in one of our cell organelles, the mitochondrion, descends from a female that lived then. But the rest of our DNA, the vast majority of it, descends from other ancestors, so that each bit of our genome comes from (to use the technical jargon “coalesces back to”) a different ancestral individual. Our genome is a mosaic of bits of DNA from different people.
Mitochondrial “Eve” was the ancestor of only our mitochondrial DNA. It’s extremely improbable (I’d say the chances are zero) of any other gene not in the mitochondrial DNA descending from this same woman. Blakemore does allow that the big-brain mutation could have occurred in a “relative” of Eve, but that’s not necessary either, except in the sense that all humans living at that time were relatives because they shared a common ancestor.
2. There’s not the slightest bit of evidence that this large increase in brain size resulted from a single mutation in the DNA. Yes, the increase in brain size may have been geologically sudden, but we can get things that would look instantaneous in the fossil record through a sudden bout of natural selection that fixes several or many genes over a relatively short period, say thousands of years. A punctuated pattern of evolution does not necessarily point to the occurrence of single “macromutations.” Steve Gould sometimes made this mistake when talking about punctuated equilibrium.
Blakemore has every right to theorize about macromutations, but in a public lecture (or interview) it would be seemly if he mentioned the problems with his “macromutation” idea.
One is that a big change in brain size without a corresponding increase in skull size probably would have been maladaptive, if not fatal. It’s much more likely that brain and skull co-evolved gradually due to the accumulation of several to many mutations, which is normally how the evolution of complex traits occurs in nature. Too, the brain is plastic, but is it plastic enough to suddenly accommodate a 30% increase in volume without evolutionary changes in wiring? Finally, the usual finding when you look at the genetic basis of “complex” adaptations in the wild (and I’m talking about things other than color, or the disappearance of traits like stickleback spines), it’s almost always due to more than one gene.
3. Finally, perhaps the biggest problem with Blakemore’s suggestion is this: if the mutation wasn’t favored by selection, how did it get fixed? He says that the big-brain mutation was initially “neutral”—that in fact it normally would have been disfavored because a bigger brain eats up too much metabolic energy, but was tolerated because there were lots of foods and resources around. Then, when the environment became leaner and meaner, that big mutation would show its adaptive effects. To repeat from above:
The environment of early humans was so clement and rich in resources that this greedy new brain, which would have absorbed even more of the body’s energy, could be sustained without danger. Later, when times got hard, during droughts or climate changes, it helped us deal with these crises, which could otherwise have killed us off, by dreaming up novel ideas to problems.
This scenario invokes a big brain as a preadaptation: a trait that just happened to be hanging around but then became useful when the environment changed. Note that Blakemore is claiming more than just that the macromutation stayed around at low frequencies because it was tolerated during fat times and then later became fixed through selection when times got tough. Rather, he’s asserting that the mutation swept to fixation without natural selection. Again:
In other words, they say simple natural selection explains what happened.
So what is your take on this view?
I think they’re fooling themselves. There was very little change in human behaviour at this time, as far as we can see from the fossil record – certainly not one that is explained by a sudden jump in the size of the human brain.
I find this scenario pretty implausible. Implausible not just because you need other changes in the body (like a bigger cranial capacity and perhaps some new wiring) to accommodate a brain that is suddenly 30% larger, but because Blakemore gives no explanation for how a big mutation that has no effect on fitness (or even a slightly negative effect) swept through the population in the first place (i.e. gets “fixed” as we geneticists say). A mutation can be “tolerated” in a species, but that doesn’t explain why it spreads through the population until everybody has it. It seems much more likely that changes in brain size, since they were sustained over millions of years of evolution, resulted from natural selection.
Granted, we don’t know what kind of selection. There are as many theories for the evolution of bigger human brains as there are theorists. Suggestions have included the advantages of big brains for hunting, for living in social groups, for attracting females, for trying to suss out the intentions of your fellows, for using tools, and so on. This is one of the questions whose answer we may never know. All scientists must live with the idea that some answers are simply beyond our ken. (That’s why it’s easier for us to not invoke gods to explain the unknown.)
But I think that Blakemore’s own suggestion is deficient in several ways. The Guardian can’t point them out in an interview, but that’s what websites like this one are for.
I have to say that although lots of people concoct evolutionary stories about humans, many of those folks could benefit from a little acquaintance with population and evolutionary genetics.
Blakemore’s “Bayesian Conjecture Lecture Series.”
Just a thought: you say that a big change in brain size without a corresponding increase in skull size would have been fatal. Probably so; but from what little I know of evo-devo, isn’t it possible for this to happen at the same time? Say there was a mutation causing increase in cranial capacity – the stem cells know there ought to be tissue in there, so it gets filled in with brain. I wonder if it’s even possible that the initially larger brain is too undifferentiated to have much of a corresponding increase in intelligence; that subsequent evolution refined its functionality.
I agree that it’s implausible – there would have to be a corresponding degree of neck muscle increase to support the head, etc. – but implausible things seem to happen all the time in biology.
Completely agree that it would be very improbable for such a feature to become fixed in a population by drift alone. Maybe sexual selection though?
Note, though, that you are invoking at least two OTHER mutations, not just the one big-brain mutation.
The problem with any sexual-selection hypothesis for brain-size evolution, I think, is that, scaled to body size, male and female brain size is about the same. If sexual selection operated (presumably on males?), you’d expect one sex to have bigger brains than the other.
Good point on sexual selection.
Why two other mutations though?
I was thinking of a way for one mutation – increase in cranial size – to take advantage of existing tissue plasticity and come up with a bigger brain. Clearly other mutations could later make this more functional, but it’s that first step that makes the whole thing workable.
Why couldn’t sexual selection work on both sexes at once? Maybe both males and females were attracted to larger-headed mates.
Maybe the big headed types had less protruding eyebrow ridges and so larger-looking and more attractive eyes.
Maybe they just gave better head.
(I’m being facetious, but I’m just a layman who doesn’t understand why sexual selection has to be one-way.)
Jerry, what about the possibility in primates of sexual selection not for size, but for functional dimorphism, as cautiously suggested by Lindenfors et al. 2007 (doi:10.1186/1741-7007-5-20), with a tentative “cultural” feedback loop at the population level as proposed by Lind and Lindenfors 2010 (doi:10.1371/journal.pone.0009241) ?
I suppose the proposed “macromutation” could spread throughout the population just by genetic drift (couldn’t it?), although this seems to me to be the least likely option for its spread!
Yes, this is of course a possibility. I just think selection is more likely and, at any rate, Blakemore doesn’t mention how the mutation was supposed to have spread.
Our large brains require such a huge investment that the genes that create it cannot be neutral.
This scenario does not explain the large brain size of Homo Neanderthalis which is actually slightly larger then Homo Sapiens (both about 1400 cc). It also doesn’t explain the brain size of Homo Heidelbergensis which, at 1200 cc is a lot closer to Homo Sapiens then 30%.
http://www.anthro.fsu.edu/people/faculty/falk/Handbook_V2.htm
Thanks, that was interesting, I look forward to reading it.
“the high intelligence of today’s primates flowered from trends in primate brain evolution that reach back into deep time (Radinsky 1974).”
Looks like a complex process is suggested, with coevolution (if that is the correct term) between overall brain size and sizes of different structures.
Meanwhile, it seems to me some simple theories may explain the lower limit on brain size though:
Social Bees Have Bigger Brain Area for Learning, Memory. The (plastic) size of some structures actually seem to reflect demands put on them (as observed on “social” vs “non-social” bees in the same species). (Which ties back to the question of sizes of specific structures, of course.)
In an area where results seems scarce, it is encouraging.
Apparently we have the same objection, but you were a lot faster than I was. (There were no comments yet when I started typing and editing.) See my post below.
Blakemore seems to continually pick the least likely option at every stage. I think that central “wish” is that the human brain got big for no adaptive reason. I’m not sure why he’s so attached to this idea, but I think that this virtually forces him to make the two other improbable claims, namely that:
1. Macromutation is the explanation for the significant morphological change, rather than several smaller (more probable) ones.
2. The (macro)mutation spread throughout the population by drift, not by selection. This despite it supposedly having a slight (or more probably massive) deleterious effect.
Hmmf.
By the way, Jerry, this was yet another fantastic post. I really do enjoy reading your reviews of all things evolutionary.
So many questions, so many alarm lights flashing, I don’t even know where to start, so I’ll limit myself to just one:
Where, in Prof. Blakemore’s scheme of hominid evolution, do the Neanderthals fit in?
If I understand the common usage of ‘Mitochondrial Eve’ MRCA correctly, as in the specific context of the Blakemore interview, it is restricted to the H. sapiens sapiens clade.
Taking the long view (leaving aside the most recent ten kiloyears), the Neanderthals deserve the ‘superintelligent species’ accolade every bit as much — or as little — as we do. So, assuming for a moment that Blakemore’s single macromutation hypothesis were correct, it should have happened at an earlier branching point.
On the other hand, I suppose Blakemore is right about brain plasticity and knowledge. But, from an evolutionary point of view, this would seem to invalidate his previous argument about the improbability of ‘unused capacities’ sitting around for 200 kiloyears. Following Blakemore’s reasoning, while assuming a biologically stable H. sapiens sapiens, why the exponential rate of cultural change in the last milennia/centuries/decades? (Just a provocative countefactual hypothesis. I don’t believe Blakemore would postulate a post-glacial macromutation instead of a cultural explanation. It’s so easy — and so tempting — to confuse cultural and biological processes and timescales during the Palaeolithic.)
Tangentially, David Deutsch had a nice take on this at a recent TED lecture:
http://www.ted.com/talks/david_deutsch_a_new_way_to_explain_explanation.html
Thanks, that was interesting too. It is obvious that Deutsch has expanded on his ideas, and I will add “robustness” as a desideratum for theory up and above the robustness through rigidity that interconnection of hypotheses and theories engender.
However, I’m not entirely happy with Deutsch ideas.
First, he is entirely too embracing of philosophy on the matter of empiricism.
(Well, no surprises there! 😀 But the fact is that even though for example his demolition of solipsism is elegant and stronger, it is enough to ask “where is the evidence”, in the same way that we can say stronger things on theism but that question is really enough.)
Second, he is entertaining the idea of “explanation”, where he reverses the order of testing being the strongest criteria and “beauty” measures such as parsimony or robustness being weaker. (He even specifically says something along those lines in this talk.) The problem with that is that testing passes testing, but beauty measures on theory can’t be tested as such.
[Parsimony, and likely robustness, can be shown to minimize reversals, they don’t actually arbitrate on theory or between theory.]
That is a long way from theory as it is commonly understood, I think.
That said, he does bring up the characteristics and problems of crypto-inductivism in his book. (Which is profiled on TED.)
For that, if not for his “crypto-explanativism”, I’m eternally grateful.
Thanks for the critique of the Deutsch talk.
Re parsimony, I wonder whether you and Deutsch are really at odds. Towards the end of his talk, he states: “That the truth consists of hard to vary assertions about reality is the most important fact about the physical world.” The ‘hard to vary’ quality is actually his pièce-de-résistance. When a hypothesis has been tested, found valid, and cannot be varied within a given framework of knowledge, is it not, by elimination, the most parsimonious within that framework? (OK, I’m prepared to get spanked epistemologically. 🙂 )
“There are as many theories for the evolution of bigger human brains as there are theorists. Suggestions have included the advantages of big brains for hunting, for living in social groups, for attracting females, for trying to suss out the intentions of your fellows, for using tools, and so on.”</i
It seems to me that big brains/intelligence is an adaptation that should have many, many causal factors. I think of human intelligence as a generalized tool – useful for a variety of different purposes – a single cause would create pressure for a single adaptation.
I don't buy the argument that:
“The environment of early humans was so clement and rich in resources that this greedy new brain, which would have absorbed even more of the body’s energy, could be sustained without danger.”
If survival is so easy, then the population increases to the point that survival is not easy – simple Malthusian population theory. A brain that is has much greater metabolic needs that doesn’t have some compensating advantage is still not going to have an easy time spreading though out a population.
Isn’t the problem here that such a population theory is rejected by experiment – AFAIU few natural populations crashes in accordance to that theory? (They and/or their predators recover et cetera – different model.)
That, and that there doesn’t seem to be a connection between malthusian theory and fixation.
Following up on your post, I discovered that his actual lecture is posted at the Royal Society web site. I hope to find time to watch it soon.
Link:
http://royalsociety.tv/dpx_royalsociety/dpx.php?cmd=autoplay&type=solo&dpxuser=dpx_v12&pres=479
Just finished watching the video: a bust, and the questions…meme selection, memic systems? I mean he is done remarkable good work in plasticity and other areas but..sigh…..constraining our own evolution? Great effort Dr Blakemore.
Thxs Dr Zimmeryngula for pointing to the link.Good exercise in “restrain”..for a sunday. The graph showing the “sudden” jump in homo brain volume is, well, insufficient, and as it has pointed out has many facets that arent considered. Was waiting for the “macromutation” clincher: didnt come, or maybe I missed it.
Watching the lecture, it’s easy to see how the brain size part is really not central to Blakemore’s thesis. I wonder why he got side-tracked on that in the Guardian interview.
Also, what statistical devil rode him to see a ‘jump’ in hominins’ brain volume, where available data (e.g. his own slide, but also the Falk paper linked by John Danley) depressingly allow for not much more than linear growth?
Is this the Dogmatic Groupthink&tm; of Darwinianism I keep hearing about?
Dr Blakemore has plasticity as a main qualifier in his title,thence ill wait to watch the lecture, but arguing there was a sudden increase in brain volume for H. sapiens is not warranted by the scant evidence. It is more cogent-to me- to argue that when one contrasts the known lineage brain volumes before sapiens, incremental increases in volume are apparent for each genus. From australo, to habilis, to erectus, to sapiens so forth. Every post lineage shows an increased skull capacity, which says very little if nothing about the cognitive “abilities” of the beholders. Cristopher Walsh at Harvard and Bruce Lahn-the ones I know-have published work on human microcephalia that could point to genes involved in increading volume by regulating cell number and brain architecture(Both have published review not lon ago, and of course there is the wonderful solid Dr Holloway).
Quick observation from a non-biologist. Could a macromutation that produces big brains and big heads be neutral unless it also, coincidentally, caused the necessary widening of the female pelvis? [shrugs]
You know, that’s a REALLY GOOD point!!!
Another developmental limit on cranial capacity is the geometry of the female pelvis. All those big-headed babies have to get born, you know. Human mothers have markedly more difficult and dangerous labor than most mammal species (with the exception of the hyena), precisely because human babies have such freakishly huge heads.
Increase in cranium size means either (1) increase in fetal cranium size, or (2) increase in cranium growth after birth. The former requires mama to have wider and wider hips. The latter requires the plates of the skull to stay unfused for longer, risking brain damage due to trauma, as well as various sorts of malformations and defects.
It’s reasonable to suspect that the human brain got as big as it could without putting survival at risk due to these or other factors.
In fact many women would and do die delivering an infant with a large head. We who survive with manageable tearing consider ourselves lucky. Unlucky are those that easily deliver children with abnormally small heads…
“Suggestions have included the advantages of big brains for hunting, for living in social groups, for attracting females”
Oh yeah, women loooove big brains in men.
I would have ranked the “single mutation” as the biggest problem with Blakemore’s claims. Presumably he makes such a claim because he’s identified the specific mutation – if not then he’s just spouting bullshit like a priest. I just have to laugh at his claim that humans had big brains but didn’t really need them, and yet he goes on about some beast sprouting wings and not using them for so long, then suddenly deciding to fly. It would appear that Blakemore may have a big brain but he hasn’t decided to use it yet – he probably doesn’t need it in this time of plenty. And there’s another laughable idea – that somehow earth was an Eden all those years ago. Food just came out of nowhere – perhaps it rained down from the skies? I never realized that the hunter-gatherer was a recent development which came about by the extinction of our smaller-brained evolutionary relatives.
“I have to say that although lots of people concoct evolutionary stories about humans, many of those folks could benefit from a little acquaintance with population and evolutionary genetics.”
Indeed, much what I thought while reading your post. But the reason he won’t try to acquaint himself is that he’s a NEURObiologist. They’re special. They have their own departments and don’t sully themselves with that which comes under the purview of mere biology.
I just thought I’d come back and toast some marshmallows next to the burning stupid.
“In short, Homo sapiens is a genetic accident.”
As opposed, of course, to all other life forms which were designed by some deity.
Jerry: “It’s extremely improbable (I’d say the chances are zero) of any other gene not in the mitochondrial DNA descending from this same woman.”
Is it really zero, or just low probability? Are we really that unlikely to have inherited any nuclear DNA from “Eve”?
We have a discussion on the topic going here: http://secularcafe.org/showthread.php?p=120550#post120550
I suppose it’s plausible that big brains got fixed in an isolated population due to the founder effect, and that this was how the “preadaptation” came about… but although that’s plausible, in the absence of powerful evidence to support it, it just seems more likely that it was due to some form of selective pressure.
I suppose it depends how you parse it. Certainly there would be genes that Eve had and that we also have. But that there was a specific mutation that arose in Eve that is present in all of us? Effectively impossible, I would think.
Children, can you say “special pleading”? Now try, “Man is the animal that rationalizes.” Blakemore’s
wild-assed guessfanciful hypothesis is just the latest in a long string of tales that humans are somehow special and singled out for greatness by natural or extra-natural causes.Yup, what you said.
It is SO hard for us to not see “high intelligence” as the point of all reality. “Just take a look around! I’m highly intelligent; and I’m the center of the universe, ergo…”
But, just look at the last 3+ billion years. Divide the number of species that evolved human-like intelligence over the number of species that have ever existed… and suddenly it doesn’t look all that adaptive.
It is my understanding that the brain of Homo Erectus increased about 30% (from around 900cc to 1200cc over the course of a million and a half years, and that skull casts clearly indicate speech capacity. We have a somewhat larger brain (1350cc), but not dramatically so. What is the evidence of a sudden recent expansion in brain size of which Blakemore speaks?
I just stumbled about this article because I’m trying to re-read what Blakemore told in a lecture I heard a year ago (FENS meeting, Amsterdam). So, maybe I can clarify one thing. (Pardon if I repeat something that has already been said in the comments; I didn’t read all of them.)
It’s about the much-discussed macromutation. In the lecture, Blakemore showed a picture from Chenn & Walsh (2002), Science 297: 365ff. In that article, it was shown that a mutation in beta-catenin (truncation at the NH2-terminal) leads to dramatically increased brains and skulls in mice, even with gyri!
So, no “macro”-mutation is needed, and the skull does (of course!) adapt to brain size.
As you see, I was quite intrigued by Blakemore’s idea. He went on pointing out that the function of cortical areas is in many cases defined plastically during postnatal development, i.e. by culture. So, an increased cortical surface in Homo sapiens may have been a preadaptation, allowing to use the vast and barren neocortex for cultural achievements like language.