I cannot resist a comment: most of "The Gay Animal . . ." is based on a near universal misreading of Darwin. The reasons for this are many and complex, and those are only the ones I recognize. First, "nasty brutish and short" is Hobbes, not Darwin; "nature red in tooth and claw" is Tennyson but often erroneously associated with Darwin. Darwin's theories are not based on "survival of the fittest", but on the relatively greater survival of the offspring of those whose traits do not overly handicap them relative to others.

Does not slip trippingly from the tounge, does it. That is one of the reasons for the consistent misstatement of the theory. It is easier to say that something was "evolved for a purpose" than that eons of nudging produced an eye or a human. "Teleology", purpose-driven evolution, was the name for what is today called "intelligent design" and precisely what Darwin was arguing against; an argument he won hands down, and given the nature of science, an argument he has won every day for more than one hundred and fifty years.

That is another reason for the misunderstanding of Darwin: if you cannot destroy a revolutionary idea, and Darwin's would not go away, you normalize it back to the status quo ante. You evolve Natural Selection back to the argument from design. The author refers to "the standard account of Darwinian sexual selection", but that is not Darwin.

A couple of points: first any simplistic idea that only individuals who contribute genes to procreation can continue should be finally put to rest by considering, e.g. the worker bee. They are sterile, they are myriad, they are highly evolved. I may not have the "correct" explanation how we got here, but one that says worker bees cannot exist clearly is inadequate.

Second, the philosophical transformation that enabled Darwin's theory--Wallace had the same idea at about the same time--was the appearance in language (around 1750) of a new definition of "individual". (This development also enabled the American Revolution.) In biology, "individual" is what we call a single human or bee. Before the transformation (this is the "for dummies" version, not because I think you are dummies, but because neither of us has time for a book, just now) the perception of "individual" was the expression of a "type". Thus each human was an imperfect example of a perfect ideal or "type". (This view allows for original sin, as well: there is a perfect man and you are not he.) Since the ideal was unchanging, there could be no evolution of species. Individuals had different color hair or longer legs, but these were mere variations in inessential characteristics. Things should stay as they are and be comprehensible to simple minds.

Around 1750, a new meaning arose that described each individual as an expression of its own individuality, grouped into species according to our, oh so imperfect understanding of what traits are important, not by original, devine writ. Individuals were different from each other in important ways, not merely cosmetic variations. Individuals could pass on traits to their offspring, and the ones who had more offspring who in turn had more offspring--whether through virtue or dumb luck--would pass on more traits to future generations than the others, thus bringing about meaningful change in the nature of the species.

What is important in all of this, since we are not having a course in Darwin, is that important differences, unpredictable differences, are absolutely essential to his thought--the sine qua non--therefore anyone who gives you a simple, simplistic, binary explanation of evolution, completely misses the boat. The claim that either a trait is "adaptive" or it is doomed, is not serious biology. Lots of variation is necessary. Most of it will not have consequences; variation that has consequences has consequences. There is no moral component; there is no standard against which to measure "fittest"; the "environment" to which adaptation is useful is almost exclusively other creatures and thus mutable. What is useful today may be counterproductive tomorrow. The evolution of one species, or group, may so alter the "environment" as to materially change what is "adaptive". (This is the Baldwin Effect.) Interestingly, that does not prevent many people who propose such explanations from being extraordinarily successful biologists, or even from being successful theorists of biology, given that even among such scholars, misunderstanding of Darwin's perception is common.