I object to the statement "our behaviors are shaped in ways that increase our fitness follows necessarily from the theory of evolution."

That is a individual-centered view of evolution. But evolution works on genes, not individuals. Had you said "our behaviors are shaped in ways that increase the fitness of our genes" then I would have agreed.

In your second paragraph, you said "Also, there are multiple levels when considering optimal behavior."

I disagree. There is only one level - that of the genes. If you're a Tasmanian devil and part of you mutates to produce the cancer which is devil facial tumor disease, and that cancer spreads to all of the other Tasmanian devils, and kills off the species, then evolution doesn't care. That set of genes managed to transcend the individual and survive without it. (Which is a good thing since it kills its host.)

Elsewhere in this thread I gave a model where two independent mutations occur at effectively the same time in the same person. One is a big advantage, the other a minor disadvantage. Both together still convey a big evolutionary advantage. This means that the minor disadvantage is very likely to spread into the entire population, because it's part of the same genome as the big advantage.

We see this all the time. As a trivial example, about 8% of our genome is made up of endogenous retroviruses. These are viruses which incorporated themselves into our DNA, and then a host mutation killed them off. They are no longer do anything for us. But our body spends a slight amount of energy transcribing them. No advantage plus slight disadvantage => net negative. Still, the evolutionary pressure to remove those bits of dead retroviruses is so weak that they have persisted for millions of years. We share some of that DNA with chimpanzees, for example.

There was likely never a time when those genes gave any advantage to an individual or even were net neutral, which is why I object to the statement "behaviors that are detrimental get weeded out."

Your statement assumes an infinite amount of time in a stable background - but species live for only a few million years (on average) and the background is always changing, so your statement isn't useful.

Yes yes, I read the selfish gene too. I don't mean that as a slight, as most of my significant understanding of evolution comes from that book. Yes, ultimately its about genes attempting to propagate themselves. But completely ignoring higher "levels" of selection is overly reductionist. It's like saying consciousness is simply chemical reactions firing in the brain. While technically true, this analysis is not at the correct level of abstraction for maximum understanding (also the same reason why we don't program in assembly).

Genes create behaviors in their host organisms. This is a large class of affects that genes have that ultimately exert selective pressures. This is the correct level of abstraction to understand this mechanism. Similarly for analyzing unfit behaviors for an individual that are ultimately fit for the group as a whole, thus the behavior is not completely weeded out.

I haven't read "The Selfish Gene" though I know of Dawkins' views. My original basis for understanding evolutionary thought comes from Gould, and you can see that influence here in my opposition to the view that behaviors have a direct genetic basis. Wikipedia summarizes his (and my) viewpoint nicely:

Gould's primary criticism held that human sociobiological explanations lacked evidential support, and argued that adaptive behaviors are frequently assumed to be genetic for no other reason than their supposed universality, or their adaptive nature. Gould emphasized that adaptive behaviors can be passed on through culture as well, and either hypothesis is equally plausible. Gould did not deny the relevance of biology to human nature, but reframed the debate as "biological potentiality vs. biological determinism". Gould stated that the human brain allows for a wide range of behaviors. Its flexibility "permits us to be aggressive or peaceful, dominant or submissive, spiteful or generous… Violence, sexism, and general nastiness are biological since they represent one subset of a possible range of behaviors. But peacefulness, equality, and kindness are just as biological—and we may see their influence increase if we can create social structures that permit them to flourish."

My resolution to the issue is to take the strict view that biological evolution only deals with genes, and that other mechanisms can be and are better at describing what you've termed the "higher levels" of selection.

The usual analogy is to computers, where software is constrained by the hardware, but still highly flexible. My own analogy is to think of weather. Fundamentally it's based on quantum mechanics, and at a higher level as particle dynamics, but weather forecast models use neither approach because because the minutia of those lower levels -- the detailed collision dynamics of a specific O2 against an N2 for example -- don't appreciably affect the large-scale weather. In fact, non-quantum mechanics can give rise to similar effects. There is no need to consider the effect of the weak force in order to predict tomorrow's weather.

Instead, weather is much more tractably understood as the gas law, along with parameters for "turbulent diffusion, radiation, moist processes (clouds and precipitation), heat exchange, soil, vegetation, surface water, the kinematic effects of terrain, and convection." It's absolutely true that weather is based in quantum mechanics, but it's not true that a quantum mechanics approach is the best way to understand the weather.

And I assert that that is the same for higher level behaviors, including even culture. Yes, there's an ultimate genetic basis somewhere in the depths, but a natural selection model based on genes is a poor instrument for understanding most human behaviors, and the attempts to do so have all had a sense of post hoc justification rather than having good experimental evidence.

Eg, just because certain dynamics models give rise to, say, homosexuality in a population, doesn't mean that those models reflect the actual process which gave rise to homosexuality in humans. It only means that gene-based evolution does not preclude an evolutionary model for homosexuality.

In any case, I gave a specific example of how an unfit behavior can spread to the entire population. It arises through a mutation, and that mutation happens to be in the same genome as another recent mutation which greatly improves fitness. This unfit behavior is both unfit for the individual and unfit for the group, but the negative consequences are so minor that there's little evolutionary pressure to weed it out.

I even gave the specific example of the endogenous retroviruses, which compose some 8% of our genome, which take some energy to maintain, and some of which are believe to have been inserted during a plague some 60 million years ago, though some are more recent. I find it hard to believe that any of those genes were ever beneficial to an individual or to the group, and yet after millions of years they still have not been fully weeded out.

(I do realize that these remaining sequences do not cause overt behavior. About all they do is take up time and energy during cell duplication. But that's still a behavior, and you have not placed a limit as to what evolution considers as a behavior or not.)

Thanks for your detailed response. I originally misunderstood your point, I thought you were essentially arguing a reductionist view of considering genes and only genes. I agree with much of what you have written, although I personally would fall more on the biological determinism side, where our genes constrain our behavior far more than people generally accept. But that's just my personal view and its certainly up for debate.

My personal view is that the belief in biological determinism is too widespread. Up until the mid-1800s, nurses were often men. Nightingale's views played a big role in making nursing a female dominated field, partially justified by saying that women are naturally nurturers. It's all too easy for people to argue that sex-based, race-based, etc. roles have a biological basis, when it's actually cultural determinism. And we know this because things have changed in timescales that aren't possible under a genetic basis. But it's easier to assume things are because they are than it is to change one self and the views of others.

In any case, I think this thread is nearing the end. I thank you for your participation and consideration.

And my thanks to everyone who chimed in. I found it an insightful discussion. A great example of the reason to keep reading the comments on Hacker News.

> this analysis is not at the correct level of abstraction for maximum understanding

That, by the way, is exactly the reasoning I used when dismissing the claim that "women have affairs to increase the genetic diversity of the sperm that compete for her egg". There are various different depths of causality and levels of abstraction at which one could view women having affairs. That particular level is one which provides almost no explanatory benefit.

(Unrelated point below.)

In addition, it may also be wrong. At previous points in time scientists have claimed that there was an "obvious" evolutionary reason why women DIDN'T have affairs. The argument, as I have heard it, states that in primates the male of the species gets the most genetic diversity by having as many children as possible with as many females as possible. But since the female is limited by biology to a fairly small number offspring, she is better served (evolutionarily) by remaining loyal to a single male in order to increase the degree to which he will help provide for her offspring and thus increase their survival rate. (Remember: it's not the number of offspring, it's the number of offspring times their survival rate that counts.)

Of course, this theory was in vogue at a time when lots of people (erroneously) believed that men had affairs but women didn't. MY conclusion is that it's extremely easy to fool ourselves with evolutionary-sounding excuses for social and cultural behavior and that one should approach any such explanation with extreme skepticism.