Can the neutral theory of evolution explain what makes us human?
|April 1, 2014||Posted by vjtorley under Intelligent Design|
When it comes to explaining the origin of complexity, evolutionists are a house divided. Here’s what Professor Richard Dawkins has to say on the subject:
I have written many times that natural selection is NOT the only mechanism of evolution. I have said it is the only known mechanism of ADAPTIVE evolution. And I’ll say that again. Natural selection is the only known mechanism of adaptive evolution, meaning the evolution of complex adaptations carrying the illusion of design. If you have another candidate not involving selection, let’s hear it. (Source, November 26, 2011.)
Compare that with what Professor PZ Myers wrote recently, in two posts which are provocatively titled, The fundamental failure of the evolutionary psychology premise and Complexity is not usually the product of selection (December 10 and 11, 2012):
…[R]andom genetic drift, the variation in a population caused by sampling error, is far more significant than most people (including most evolutionary psychologists) assume.
Why? Because selection is blind to small differences. Chance dominates, unless the selection coefficient is relatively large.
What that means is that selection works best in large populations, while chance dominates in small populations…
What it also means is that in any population there will be a range of variation that is effectively invisible to selection, a range that will be rather narrow in an immense population of bacteria, but will be relatively wide in small populations…like, for instance, a large, slow-breeding population of Pleistocene primates. [PZ means humans, of course – VJT.]
I’ve been assured that this is a decent summary of evolutionary psychology by a credible source. If you understood what I wrote above, you’ll immediately see the problem.1. Organs are complex functional adaptations, results of selection processes.
2. The brain is an organ.
3. Therefore, we can understand it in terms of the past, just as we do for every part of the body in humans and in all other life forms on earth.
First of all, let’s just dismiss that “complex” quantifier. It’s irrelevant and often not true…
…[C]omplexity usually isn’t a product of selection, but primarily of chance.
I think if selection were always the rule, then we’d never have evolved beyond prokaryotes — all that fancy stuff eukaryotes added just gets in the way of the one true business of evolution, reproduction…
Even in something as specific as the physiological function of a biochemical pathway, adaptation isn’t the complete answer, and evolution relies on neutral or nearly neutral precursor events to produce greater functional complexity.
Professor Larry Moran, like PZ Myers, is a big fan of the nearly neutral theory of evolution, which states that “the fate of mutations with only slight positive or negative effect on fitness will depend on how population size affects the outcome.” (Myers explains the differences between the selection theory of evolution, the neutral theory and the nearly neutral theory here.)
Professor Moran’s view: 22.4 million neutral mutations were what made us human
In a recent post dated April 2, 2014, Professor Larry Moran clarifies his position:
At no time have I ever denied that natural selection plays a role in the evolution of humans. It would be ridiculous to do that…
The differences in the complexities of chimp and human brains are almost certainly due, in part, to adaptation and fixation of beneficial alleles by natural selection.
As I do not wish to be accused of intentionally misrepresenting Professor Moran’s views, I invite readers to peruse his latest post and judge its merits for themselves. I would also like to apologize for unintentionally misinterpreting his views on human evolution.
I would also remind Professor Moran that when two people whose views on a subject are poles apart try to enter into dialogue, mutual misunderstandings are bound to occur. Accusations of lying are therefore unhelpful.
I should add that since Professor Moran’s Sandwalk blog is just the click of a mouse button away, it would be senseless for me to try to intentionally misrepresent his views.
Finally, for the record, I do not regard evolutionary biologists as stupid, as Professor Moran seems to think. I’m quite sure that many of them are a lot more intelligent than I. What I do think is that they, like most human beings, are prone to ideological bias against viewpoints which they find profoundly uncongenial, and that in attempting to discredit these viewpoints, they are liable to be swayed by emotion rather than reason. Intelligent Design is a theory which tends to make hackles rise in scientific circles.
END OF UPDATE
For Moran, the differences between humans and chimps can ultimately be explained by 22.4 million mutations being fixed in each of their genomes. Most of thee mutations (he believes) will be either neutral or nearly neutral. As he puts it:
The human and chimp genomes are 98.6% identical or 1.4% different. That difference amounts to 44.8 million base pairs distributed throughout the entire genome. If this difference is due to evolution then it means that 22.4 million mutations have become fixed in each lineage (humans and chimp) since they diverged about five million years ago.
When I expressed doubt in a recent post that an accumulation of minor mutations could account for the macroevolutionary transition leading to the emergence of human beings from a primate ancestor, Professor Moran reiterated his position:
I recently wrote up a little description of the differences between the human and chimpanzee/bonobo genomes showing that those differences are perfectly consistent with everything we know about mutation rates and the fixation of alleles in populations [Why are the human and chimpanzee/bonobo genomes so similar?]. In other words, I answered Vincent Torley’s question.
Now, I am no expert when it comes to mutations. But I do know something about human evolution – I’ve been studying it, on and off, since I was about eleven. So in today’s post, I’d like to explain some of the reasons why I don’t believe that neutral mutations (or nearly neutral ones) have a hope in Hades of accounting for the complexity of the human brain. And if it cannot account for the human brain, then a fortiori, neither can it account for the human mind. (As readers will be aware, I espouse a form of dualism: for an excellent account of why dualism is far more reasonable than materialism as an account of mind, see Professor David Oderberg’s articles, Hylemorphic Dualism and Concepts, Dualism, and The Human Intellect. Professor Oderberg is a highly respected philosopher who teaches at Reading University.)
How much time do we have?
In my previous post, I drew readers’ attention to a very strange implication of the neutral theory of evolution:
We are told that for a population of N organisms, it takes (4*Ne) generations for a mutation to get fixed in the population, where Ne is the effective size of the human population. For most of human history, the effective population size appears to have been around 10,000, even though the actual human population size is thought to have been considerably higher (350,000 from the Middle Pleistocene onwards, according to a 2008 article by Professor John Hawks). Four times 10,000 equals 40,000 generations, and if we use Professor Moran’s figure of 27.5 years per generation, that’s equivalent to 1,100,000 years ago.
Let me spell that out: if we take a typical mutation out of the 100-odd mutations which (according to the neutral theory of evolution) got fixed in the human population within the last generation (from 1987 to 2014), we will find that that mutation first appeared in the human lineage some 1,100,000 years ago.
Am I the only one who thinks this figure is absolutely extraordinary? And for that matter, doesn’t the notion of a mutation that takes one million years to fix sound a little suspicious?
Professor Moran’s barbed response was:
No, Vincent, you are not the only one who finds the basics of evolution “extraordinary” and “suspicious.” Just about everyone who posts on Uncommon Descent and Evolution News & Views is as ignorant as you.
I take, then, it that Moran accepts the figure of 1,100,000 years.
How recent changes gave rise to the brain of modern man
Now, I have argued, in a previous post titled, Who was Adam and when did he live? Twelve theses and a caveat, that true human beings likely emerged a little over a million years ago, with the appearance of Heidelberg man, the presumed ancestor of modern Homo sapiens, Neandertal man and Denisovan man. (Estimates for the date when Heidelberg man first appeared range from 600,000 to 1,300,000 years ago.) I pointed out that the human prefrontal cortex, which enables us to control our impulses for the sake of long-term goals, has not greatly changed since the appearance of Heidelberg man, who practiced monogamy and frequently sacrificed his life for the good of the tribe, when hunting (see here). That sounds pretty human to me. Of course, other writers have their own opinions regarding the cut-off point for the emergence of true human beings, but that’s my opinion.
What I’d like to point out, however, is that the brain of modern man was in many respects very different that of from his presumed ancestor, Heidelberg man. Benoit Dubreuil summarizes the differences between the two species in his article, Paleolithic public goods games: why human culture and cooperation did not evolve in one step (Biology and Philosophy 25:53–73):
The relative stability of the PFC [prefrontal cortex] during the last 500,000 years can be contrasted with changes in other brain areas. One of the most distinctive features of Homo sapiens’ cranium morphology is its overall more globular structure. This globularization of Homo sapiens’ cranium occurred between 300, and 100,000 years ago and has been associated with the relative enlargement of the temporal and/or parietal lobes (Lieberman et al. 2002; Bruner et al. 2003; Bruner 2004, 2007; Lieberman 2008). (p. 67)
The temporoparietal cortex is certainly involved in many complex cognitive tasks. It plays a central role in attention shifting, perspective taking, episodic memory, and theory of mind (as mentioned in Section “The role of perspective taking”), as well as in complex categorization and semantic processing (that is where Wernicke’s area is located)…
I have argued elsewhere (Dubreuil 2008; Henshilwood and Dubreuil 2009) that a change in the attentional abilities underlying perspective taking and high-level theory of mind best explains the behavioral changes associated with modern Homo sapiens, including the evolution of symbolic and artistic components in material culture. (p. 68)
In other words, the temporoparietal cortex of the brain has undergone a startling degree of evolution, just within the last 100,000 to 300,000 years. This evolution of the brain has a lot to do with the explosion in human symbolic and artistic abilities, since the emergence of Homo sapiens.
In a recent paper, Somel et al. (2013) argue that human-specific cognitive abilities arose around 200,000 years ago, subsequent to the split between Neandertals and Homo sapiens, although they also acknowledge that “it is conceivable that Neanderthals and Denisovans also possessed certain types of human-like linguistic abilities.” They write:
With respect to the trajectory of human brain evolution, the existing data suggest two distinct phases: a long and gradual increase in brain size that was accompanied by cortical reorganization, followed by a more recent phase of region-specific developmental remodelling. This second phase, which led to the emergence of the cognitive traits that produced the human cultural explosion ~200,000 years ago, may have been driven by only a few mutations that affected the expression and/or primary structure of developmental regulators.
(Human brain evolution: transcripts, metabolites and their regulators by M. Somel, X. Liu, and P. Khaitovich, in (2013) Nature Reviews Neuroscience 14, 112–127, (February 2013), doi: 10.1038/nrn3372. The full version is available online.)
The authors also note that “among 23 genes harbouring amino acid changes at conserved positions that are human-specific and not shared with Denisovans, eight have roles in neural and synaptic development” (p. 119).
Readers will recall that one implication of the neutral and near-neutral theories of evolution espoused by Professors Myers and Moran was that new traits should have taken 1,100,000 years to get fixed in the human population, if they were the product of neutral (or near-neutral) mutations. But here we have a biological trait that shaped the course of human history, that did not exist prior to 300,000 years ago!
Heidelberg man was no dimwit
Now, I don’t want to overstate my case here. Heidelberg man was no dimwit: as I pointed out in my post on Heidelberg man, he was evidently capable of fishing, controlling fire, making complex tools using techniques that took hundreds of hours to learn, and hunting big game (a risky but rewarding activity) using stone-tipped spears. Heidelberg man also practiced compassion in a very human manner: individuals with severe physical and mental abnormalities were taken care of by their tribe for a period of several years. For my part, I believe that Heidelberg man did indeed possess language, and that he also possessed some degree of artistic ability. In their review of recent research, titled, On the antiquity of language: the reinterpretation of Neandertal linguistic capacities and its consequences (in Frontiers in Psychology, 4:397. doi: 10.3389/fpsyg.2013.00397), Dan Dediu and Stephen Levinson argue that the Neandertals’ advanced cultural behavior, coupled with their vocal capacity to produce language, suggests that they actually used language. If both modern humans and Neandertals used language, then it’s reasonable to infer that their last common ancestor, Heidelberg man, did as well. And according to a 2011 paper, The First Appearance of Symmetry in the Human Lineage: where Perception meets Art (careful: large file!) by Dr. Derek Hodgson (in Symmetry, 2011, 3, 37-53; doi:10.3390/3010037), tools dating from 750,000 years ago, created either by Heidelberg man or late Homo erectus, have been unearthed in Africa. The design of these tools manifests a concern for three-dimensional symmetry on the part of their makers, which is a clear indication of artistic ability. (See also the discussion of the Master hand-axe here.)
Nevertheless, it seems that the features that distinguish Homo sapiens from his predecessors are of relatively recent origin, and the date of their emergence in the fossil record does not fit with the predictions of the neutral theory of evolution. Moreover, since these features were apparently responsible for an explosion in cultural creativity in human beings, they can hardly be describe as “neutral mutations.” If a trait that dramatically enhances creativity is not a beneficial mutation, then nothing is.
Earlier beneficial mutations that helped make us who we are
In their article, Evolution of the Brain in Humans – Paleoneurology (in The New Encyclopedia of Neuroscience, Springer, 2009, pp. 1326-1334), Holloway et al. chart the evolution of the human brain over the last four million years. They emphasize that the prefrontal lobe has changed very little in the past few hundred thousand years: “The only difference between Neandertal and modern human endocasts is that the former are larger and more flattened. Most importantly, the Neandertal prefrontal lobe does not appear more primitive.” I cited Dubreuil’s article above, arguing that the prefrontal cortex reached its modern form with the appearance of Heidelberg man (the presumed common ancestor of Neandertal man and modern man) and that it enabled our ancestors to control their impulses while pursuing long-term goals. Again, it is hard to see how this could be anything but a beneficial trait.
In their article, Holloway et al. chronicle two earlier events in the evolution of the human brain, which would also have clearly benefited our ancestors:
At least two important reorganizational events occurred rather early in hominid evolution, (i) a reduction in the relative volume of primary visual striate cortex (PVC, area 17 of Brodmann), which occurred early in australopithecine taxa, perhaps as early as 3.5 MYA [million years ago – VJT] and (ii) a configuration of Broca’s region (Brodmann areas 44, 45, and 47) that appears human-like rather than apelike by about 1.8 MYA. At roughly this same time, cerebral asymmetries, as discussed above, are clearly present in early Homo taxa, starting with KNM-ER 1470, Homo rudolfensis…
Certainly, the second reorganizational pattern, involving Broca’s region, cerebral asymmetries of a modern human type and perhaps prefrontal lobe enlargement, strongly suggests selection operating on a more cohesive and cooperative social behavioral repertoire, with primitive language a clear possibility.
The authors go on to acknowledge, however, that “relative brain size was not yet at the modern human peak.”
In conclusion: there appear to have been at least four changes in the development of the human brain over the last few million years, which can only be described as beneficial. In addition, the most recent of these changes emerged and fixed itself within the human population far more quickly than allowed for by the neutral theory of evolution. The neutral theory of evolution thus appears to be woefully deficient, as an account of what makes us human.
I’d like to close with a short quote from the late John Maynard Keynes. “When my information changes, I alter my conclusions. What do you do, sir?”