Evolution and Human Nature: some key ideas


-The Hopi questions…What are we? How did we get here? Where are we going?…

-Darwin’s Answer: A person is

            -A kind of animal;

            -A product of evolution through random variation and natural selection for reproductive fitness


Darwin’s Answer is


            New (in 1859)







-Correct, because evolution is inevitable given the demonstrated reality of (1) random inheritable variation and (2) correlated variation in reproductive success. (One example: pigmentation of moths during industrialization (and Kettlewell’s experiments)… 

-New,  relative to prior ideas of evolution with no proposed mechanism. Buffon, Schopenhauer; Cuvier and extinction; gradual modification (Buffon) vs separate creation of discrete types (Cuvier).

-Important:  Darwin’s idea helps understand what we now are, as products of evolution under the very different conditions of prior eras.

-Simple:  natural selection is nothing more than survival of the fittest, plus (or including) sexual selection, or reproduction of the fittest…we have been optimized for reproduction

-Universal: applies to all creatures and characteristics, including psychological ones

-Incomplete: most important idea ever ? A theory of everything….not a complete theory of anything, but has something to say about everything: “Nothing about biology (/life, behavior) makes sense except in the light of evolution”? Hardly, but the evolutionary perspective does help to make sense of everything. 

-Illuminates the most basic aspects of human existence: conflict, death, disease, suffering, sex...

            -Conflict, injury, suffering: ‘Nature red in tooth and claw’; George Williams: Mother Nature as a Wicked Old Witch.

            -Good and evil (compare ‘original sin’). When are people selfish? When are they not? Tribal morality and selective altruism, illustrated by The Ten Commandments and genocide in the time of Moses.

            -Especially, why are we unhappy/discontented so much of the time, instead of being unconditionally blissful? The Darwinian answer is that discontent is necessary to motivate us to improve our condition (for instance by resource acquisition) in ways that are favorable for our survival and reproductive fitness. Unconditional happiness would not make for success in a competitive world.

            -Sex: Why male and female? For rapid evolution; Why differences? (Nurturing/aggressive; women live longer…). Why is sex so important to us? Obviously…

            -Human rationality: a decisive evolutionary advantage, but one that can completely subvert the process of natural selection; yet evolution can help understand the limitations of human rationality. Aristotle (‘the rational animal’) vs. St. Augustine (;the animal capable of rationality’)

            -Culture: some aspects of human nature are culturally universal, some not….culture itself as an evolutionary phenomenon….especially morality…why did morality evolve? Why is altruism so often restricted to the in-group?

            -Disease: most is (was) from competition with parasites: disease for the host is health and life for the parasite…so Darwinian selection explains why we get sick, ie why there are so many parasites and why they are so good at infecting us.

            -Death: some issues that evolution can illuminate are

·                     Why shouldn’t we live 1Kyr or 10Kyr? Wallace, Darwin: death for rapid adaptation;             inevitable deterioration? (but breeding in Drosophila). 

·                     Overpopulation (lemmings?): Are shortened lifetimes a sacrifice for the good of the species?…A questionable, group selection argument…

·                     The objection to group selection: a single Methuselah with many kids, or a cheater lemming (below) could have a reproductive advantage over less long-lived conspecifics; but group selection can happen with reproductive isolation. The truth about lemmings…


Natural selection and the basis of heritable variation


            Evolution as a model for the diversity of life…Erasmus Darwin…similarities form a tree structure

            The discovery of extinction (late 1700s, Cuvier Mammoth): new difficulties for the supernatural guidance model: species die, as well as individuals. 

            But selective extinction is a small part of natural selection…heritable variation through small incremental changes can be more powerful, without requiring a discontinuous process of speciation/extinction. (Example: dogs) .

            Genetic model: mutations and (especially) recombination create diversity, generally in fairly small jumps.  Differential reproductive success within a species, not extinction of a particular genotype, is the main source of evolutionary change. Evolution requires two things: heritable variation, and variation in reproductive success.  The latter is least if resources are completely abundant, but animals including our ancestors have typically operated under resource-limited conditions. In those conditions, evolution is inevitable (MUST happen)  given the two principles mentioned. Example: peperred moths, Natural Selection Moth Example '; Ring-tailed warbler speciation


A few background concepts:

species are reproductively isolated, but important individual variation exists within each.

adaptive: technically, what is favored by natural selection, or equivalently what promotes reproductive success (not what promotes happiness, goodness, or general competence)

phenotype: observable characteristics vs genotype

polymorphism/mutation: mutations are the ultimate source of polymorphism but the polymorphism term is applied when alternative variants of a gene (alleles: 20K genes, maybe 10^4 bp each) are common enough that recent mutation events (around 10^-5 per generation per base, dozens or hundreds new in each human) could not account for them all, so they are evidently maintained in the population without drastic selection against them. Polymorphisms are at 1 per few hundred sites, so we are “all 99% the same”, just as 98%  or so of the human genome is shared with chimps…but a different 1 or 2% distinguish us from chimps than from each other.

Chromosomes: 22  times 2 +Xy or XX

Additive/non-additive variation and heritability…cake analogy; happiness depends on a combination of ambition and competence?



Sociobology, aka evolutionary psychology: 4 key claims


I.  A person is

            -A kind of animal (DNA fraction in common?= 98%)

            -A gene's way of making another gene (Konner, Dawkins); PGP (Chicken>Egg>Chicken)and GPG (Egg>Chicken>Egg) are equally valid in different ways. Obviously genes don't have desires or purposes. On the other hand, people are not replicated in later generations, as genes are…and whatever you make of yourself during your life doesn't get passed on biologically to your descendants.)


II. Humans are adapted by evolution to the hunter-gatherer social environment.


Evolution is slow, lags…cultures last maybe 1Kyr, species for millions.  Modern culture easily traceable and recognizable for a few K yrs back..but it took > 2M years (pleistocene) to become human, mostly in an ‘ancestral’ environment different from the modern one.


Crude time line: 5-6M common ancestor with chimps and Bonobo, became australopithecus..homo genus identified from about 2M back…erectus, then sapiens…Neanderthals usually classified as sapiens, 100K ago, found a little later in parallel with our ancestors, Cro-Magnon.


Side effects of "evolutionary lag":

            myopia from reading?

            Hearing loss from loud sounds, 1Khz per decade, less in Scottish Highlands where my                              immediate ancestors came from.

            Desserts and obesity. Self-control in food intake was not strongly selected for..no risk of excess

            Others?  Violence and guns…what wasn’t too much aggressiveness now is too much?

            *Foresight and saving, not much rewarded in the Pleistocene.

                        (When there’s nothing to save…no payoff for frugality)


The future (“where are we going”)…can human nature change more rapidly under sufficient pressure from a changed environment? Speed under pressure…Darwin's finches, pepper moths..reverted; domesticated foxes in a few generations (with curly tails); varieties of dogs mostly bred in past 200 years, evolved from wolves only about 15000 years ago.


Evolution can't plan ahead. Thus conservation would not be favored by natural selection, especially in mobile communities. Hence potential for despoiling of the planet. We don't naturally think in millenia, but we should, and we can. In this and in other contexts, we might do better than ‘obey’ our genes.


Evolution encourages inadequate, essentially tribal moral systems that can be seen as motivating much of what goes on in even the most sophisticated societies.  In-group (tribal) morality worked in the Pleistocene; it  can be a problem in a global community, but even now is probably favored by selective pressures. Altruism within an in-group, frequently accompanied by conflict and war between groups.  How far can rational deliberation allow us to rise above our tribal nature?  All this is obviously culturally contingent. But is it completely culturally contingent, or do inherited genetic characteristics have some relevance?


Changing selection pressures: medicine reduces selective pressure for physiological fitness, cultural complexities increase pressure for cognitive competence…


III Genetic influences on our nature are shaped by natural selection for reproductive fitness. Dawkins: we are vehicles for our genes through which they reproduce. But:

            Debates about levels of selection;

            Non-additive genetic effects, complexity…e.g. talent/ambition combine nonlinearly to influence contentment; compare balanced ingredients in a cake…



IV Despite the predominant influence of culture and individual life history in human psychological development, genetic constraints can claim at least a small degree of relevance to a vast range of human idiosyncrasies that can be observed in the everyday, things we take for granted. 


            Consider mate choice. We might say loosely or metaphorically that your genes ‘want’ to replicate themselves; they ‘want’you to choose a partner radiating youthful health and beauty, because those physical qualities are associated with fertility.


            But this obviously metaphorical language introduces dangers of misinterpretation: what does talk about what genes ‘want’ really mean?? And perhaps still more potentially misleading: what does it mean to say that you ‘want’ what will replicate your genes?


            1. Genes provide a genetic background that maximizes reproductive fitness.

            2. Starting from this genetic background, various complex developmental processes, especially socialization in a particular cultural context, shape our emotional dispositions and our values in ways that are indirectly and perhaps only weakly influenced by our genetic makeup. 

            3. What we want—the particular desires and choices that we make consciously and deliberately—is influenced (again, indirectly and weakly) by those characteristic dispositions and values, as well as by whatever conscious reflection we bring to the decision-making process.



Your own attraction to health and beauty in the choice of a partner reflects the preferences we metaphorically (and too simply) ascribe to your genes. But there are tradeoffs that may be different for you as an individual than they were for reproduction in your hunter-gatherer ancestry. These set the relative importance and priorities among a host of relevant things such as wealth, intellect, your partner's willingness or unwillingness to help with childrearing... Your parents might have a third set of priorities for choice of a partner. The tradeoff that makes you happiest might not be the one that you're genetically predisposed to make…or is it? In principle at least, it should be possible to discover whether people who marry for sex, youth and beauty, at the expense of other qualities, are or are not happier as a result that those who disregard the hypothetical pull of their genetic predisposition.  (Why might the genes make a choice that isn't right for you? One clear example: evolutionary lag; in the modern world, is the stage set for a ‘revenge of the nerds’?)



Four Pitfalls (Tempting but dangerous over-extensions of these ideas):



            I. The naturalistic fallacy: whatever is revealed as "natural" as a matter of fact is OK.  Yet, “nature…is what we were put in this world to rise above.” Thornhill example: “The Natural History of Rape”.



            Are fact and value then independent? Yes, in a weak sense, but knowing facts (including facts about what’s natural) still matters.

You can't justify any decision without ultimately appealing to some value judgment, and ultimately value judgments can't be derived exclusively from facts. You can never go immediately from an ‘is’ to an ‘ought’.

In other words, ‘ No values in, no values out’.

But: facts also have to be considered…

Ought you to go and get an MBA degree? The answer must depend, among other things, on how much you value material wealth. But it also depends on how much material wealth it can be expected to bring you, and this really a question of fact.  Your various relevant values combine multiplicatively with the actual expected gains and losses of various kinds to determine which decision will appear the proper one for you to make.

Likewise, if we ask, for instance, whether our society's taboo on sex between adults and minors is justifiable, the answer should depend on the factual consequences of that for all concerned, and at the same time on value judgments about those consequences: are those consequences acceptable?    Justification of the taboo could not be based on the facts (consequences) alone, but neither can it be independent of them.  Cultural variation…


            II. Social Darwinism: we should let the strongest prevail, and not strive for social justice; life as a forced contest for survival and reproduction…vs. man as inherently free, more or less rational and moral by nature. This is a particularly important special case of the naturalistic fallacy.

Darwinism is most usually adopted by political pundits of the right, but it doesn't have to belong there.

Karl Marx was a big fan of Darwin, even wanted to dedicate Das Kapital to Darwin, and believed that variations in genetic fitness were important for social stratification. Nevertheless, he avoided the naturalistic and the inevitability fallacy in promoting his egalitarian and arguably somewhat "unnatural" social ideal: "From each according to his ability, to each according to his need".

Did Marx's perfect society fail for biological reasons, because he underrated the role of self interest when he assumed that state monopolies could reward self-interest sufficiently? Does our collective genetic makeup predispose us to construct a stratified society?

Darwinism is commonly criticized from the left, but--Maynard Smith, Communist; Trivers, Black Panther; Peter Singer (“Darwin for the Left”)…etc.



III. The inevitability fallacy: what's "natural" is inevitable—a fallacy that often arises from a false antithesis between nature and nurture, or a misinterpretation of "genetic determination"). Compare length/width, engine/gasoline, husband and wife. Completely meaningless? Not quite, in area case….a set of rectangles might vary more in height, or else they might in width; but this wouldn't justify neglect of either factor for most purposes (although for some it could be worth knowing….cf. Headstart? Could still be seriously misled, e.g. by generalizing to unobserved environmental conditions..)

Should we consider  even culturally universal phenomena like war or marriage to be in some way inherent?? What if  they are only almost universal? Or only the result of a controllable predisposition? Or completely malleable, and only universal by accident?  How do  we assess the relative influence of genetic and cultural variables in human development?

New scope for free choice in the modern world: drugs for mood and personality; enhanced contraception. You can ‘disobey’ your genes now more than ever. (But: is it nevertheless important to recognize what is difficult to change in your own nature??)

            Because naturalism and naïve genetic determinism are both fallacies, the proper response to a demonstration that some kind of behavior is "natural" could be to tolerate, oppose it with penalties, or oppose it through education and socialization.


How the “Selfish Gene” idea can be misleading: the case against it, from Denis Noble:



            IV. The anthropomorphic fallacy: viewing animal behavior in human terms, or vice versa, e.g. "rape" (better known as “coercive inercourse”)  by mallard ducks. Are those mallards behaving badly? Should they be punished? Not a completely silly notion, but of course the concept of rape loses pretty much all the meaning that it has for us, if we apply it to a bird. So calling what birds do "rape" is misleading. And in exactly the same way, any attempt to reason about rape in humans on the basis of what animals is equally dangerous.


The evolutionary framework for the present

            We are using this here only to elucidate the present, unlike real evolutionary biologists.


Illustrative major issue: How can altruism be supported through natural selection?


General caveats in applying this framework: we shouldn't assume that everything must be adaptive. Exceptions are expected from: (1) pure chance (hippo island, long tusk). Meteorite spares long tusk hippos. (2) Side effects, e.g. sequencing and language from throwing? Sidewalk ramps for wheelchairs, are good for bicyclists as well.. (3) In group morality (tribal conflict, racism) as an extension from favoring ones kin…later

            Another caveat: the verifiability problem; just so stories…how the leopard got its spots; does evol. psych. just supply dubious rationales for what we knew already?

            Example: In the area of gender differences, wealth and physical attractiveness are traded off differently by men and women. That's the conventional wisdom, and it's been shown to have some basis in reality. But the interpretation is controversial: did this evolve as a genetic predisposition or is it culturally based?  We'll discuss this.



Timeline of human evolution