Thursday, March 17, 2011

Evolutionary Psychology: The Science of Human Nature

Having been tickled by Google Alert that my name had been mentioned in the comments at Pharyngula (P. Z. Myer's blog), I took a quick look. Just a few comments for now:

1) I became an evolutionary psychologist when studying the behavioral ecology of Microtus pennsylvanicus got boring. Those cute little field voles got boring because their ethology is relatively simple. Human ethology is a lot more interesting, mostly because it is a lot more complex. Should we not try to study it because it is more complex? Or because it might not jibe with some people's political preconceptions?

2) I assign Gould & Lewontin's "spandrels" paper to my students in evolutionary biology, along with various criticisms of it. I also assign Eldredge & Gould's "punk eek" paper and Gould and Vrba's "exaptation" paper (along with close to three dozen others, not to mention the entire Origin of Species, 1st. ed.). I also give them chunks of George William's 1966 classic, Adaptation and Natural Selection, so that they will know exactly how "onerous" the concept of "adaptation" actually is.

3) Here's the definition of "adaptation" I use:
An evolutionary adaptation is any heritable phenotypic character whose frequency of appearance in a population is the result of increased reproductive success relative to alternative versions of that heritable phenotypic character.
4) Here are the criteria I believe are most useful when one is attempting to determine if one is dealing with an "adaptation":
Qualification 1: An evolutionary adaptation will be expressed by most of the members of a given population, in a pattern that approximates a normal distribution;

Qualification 2: An evolutionary adaptation can be correlated with underlying anatomical and physiological structures, which constitute the efficient (or proximate) cause of the evolution of the adaptation;

Qualification 3: An evolutionary adaptation can be correlated with a pre-existing evolutionary environment of adaptation (EEA), the circumstances of which can then be correlated with differential survival and reproduction; and

Qualification 4: An evolutionary adaptation can be correlated with the presence and expression of an underlying gene or gene complex, which directly or indirectly causes and influences the expression of the phenotypic trait that constitutes the adaptation.
To me, it seems reasonable that if one can apply those to a specific human behavior, one can make arguments about its evolutionary derivation. Would anyone disagree?

As for the ridiculous idea that evolutionary psychology only deals with sex, has anyone making such a claim actually read a textbook on the subject? Here are several:

Human Evolutionary Psychology

Evolutionary Psychology: The New Science of the Mind (4th Edition)

Evolution and Human Behavior, 2nd Edition: Darwinian Perspectives on Human Nature

Evolutionary Psychology: The Science of Human Nature

[Full Disclosure Notice: The fourth title is indeed by Yours Truly.]

If you haven't, then please do so, and then we can discuss these questions.

While we're on the subject, Part II of Evolutionary Psychology: The Science of Human Nature (on the ethology of between-group behavior in humans) is coming out in May. My next project is an introductory textbook in evolutionary biology, entitled Evolutionary Biology: The Darwinian Revolutions, again in two parts. Part I (due out in September) is The Modern Synthesis and Part II (due out next May) is The Evolving Synthesis.

After that (if I live that long) will be On Purpose: The Evolution of Design by Means of Natural Selection (won't there be some fireworks when that comes out?), in which I present one of the core arguments for The Metaphysical Foundations of the Biological Sciences, in the spirit of E. A. Burtt's The Metaphysical Foundations of Modern Physical Science. Should be fun!


As always, comments, criticisms, and suggestions are warmly welcomed!


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At 3/17/2011 12:17:00 PM, Blogger NickM said...

"Qualification 1: An evolutionary adaptation will be expressed by most of the members of a given population, in a pattern that approximates a normal distribution;"

Eh? Why? I doubt that the presence or absence of eyes follows a normal distribution in humans, yet they are nevertheless adaptations.

At 3/17/2011 02:57:00 PM, Blogger Larry Moran said...

#1 is irrelevant because non-adaptations show the same distribution.

#2 is completely circular and therefore useless. The real question is "whether" the physical structure caused the evolution of the feature. Once you've established that the structure caused evolution then you've established that it's an adaptation.

#3 only works if you are certain you understand the pre-existing environment and the population that inhabited it. Many evolutionary biologists are absolutely certain that they know how and where our primitive hunter-gatherer ancestors lived and how they behaved. Are they correct? That's the real question.

#4 is a bummer. Most of evolutionary psychology fails to demonstrate that a given bahavior actually has a genetic component.

At 3/17/2011 08:30:00 PM, Blogger Allen MacNeill said...

The problem with using a complex phenotypic trait, such as eyes, is that such traits are the product of a suite of genetic and developmental factors.

However, if one focuses on a much simpler trait, such as bill depth (as in Geospiza fortis, then usually one does indeed find a distribution that approximates a normal distribution (or a skewed normal distribution in the case of a trait under directional selection).

This was one of R. A. Fisher's most important contributions to the theory of natural selection: that traits that show "continuous variation" are the kinds of traits that can be altered by selection.

At 3/17/2011 08:45:00 PM, Blogger Allen MacNeill said...


For your comment #1, see my reply to Nick in comment #3.

As for your comment #2, the point here is that if there is no direct or indirect structural or functional correlate to a particular DNA sequence, then the presence or absence of that sequence is of no consequence whatsoever to fitness and therefore cannot be an adaptation.

And, viewed from the standpoint of behavioral selection, if you can't find an underlying neurobiological substrate for the behavior, it is unlikely that the capacity for that behavior has evolved by natural selection.

For example, human language is correlated with specific anatomical regions of the brain (i.e. Broca's and Wernicke's areas), which if damaged result in aphasia. Therefore, it is reasonable to infer that these regions are functionally tied to language, and that the underlying genetic and developmental programs that bring about the assembly and operation of such regions have evolved by natural selection.

Your comment #3 is a gross example of a straw man argument. I know of no one – not evolutionary biologist nor evolutionary psychologist nor anthropologist nor archaeologist – who claims to be "absolutely certain that they know how and where our primitive hunter-gatherer ancestors lived and how they behaved". On the contrary, we attempt to infer the EEA of a particular adaptation by correlations with contemporary examples and diligent examination of the archaeological and fossil evidence. This is how one infers the EEA and function of the forelimbs/pectoral fins of Tiktaalik, right? Why is doing the same thing for something like inter-group warfare or sororal polygyny less valid?

And your comment #4 is yet another straw man. Konrad Lorenz, Niko Tinbergen and Karl von Frisch shared a Nobel prize for studies of animal behaviors in which not one controlling gene for any of the behaviors were identified (and for which we still have only inferential evidence). Does this mean that fixed action patterns, imprinting, sign stimuli, and the dance communication system of honey bees are therefore not valid examples of behavioral adaptations that have evolved by natural selection?

At 4/14/2011 02:22:00 AM, Blogger Saeid Mushtagh said...

can you help me answer this:

Q: How many years will it take for a biological variation (anatomical, physiological, or behavioral) that depends on as little as 5 single nucleotide mutations to randomly arise?

please post your answer to:

At 5/22/2011 07:13:00 PM, Blogger Allen MacNeill said...

As of Sunday 22 May 2011, Evolutionary Psychology: The Science of Human Nature, Part I is #45 on's list of books on evolutionary psychology. Part II will be released in June.

At 2/23/2012 06:33:00 PM, Anonymous Cindy said...

Such a great article which those cute little field voles got boring because their ethology is relatively simple. In which Human ethology is a lot more interesting, mostly because it is a lot more complex.Thanks for sharing this article.


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