Darwin’s explanation of races by means of sexual selection

Abstract

In Darwin’s Sacred Cause, Adrian Desmond and James Moore contend that “Darwin would put his utmost into sexual selection because the subject intrigued him, no doubt, but also for a deeper reason: the theory vindicated his lifelong commitment to human brotherhood” (2009: p. 360). Without questioning Desmond and Moore’s evidence, I will raise some puzzles for their view. I will show that attention to the structure of Darwin’s arguments in the Descent of Man shows that they are far from straightforward. As Desmond and Moore note, Darwin seems to have intended sexual selection in non-human animals to serve as evidence for sexual selection in humans. However, Darwin’s account of sexual selection in humans was different from the canonical cases that Darwin described at great length. If explaining the origin of human races was the main reason for introducing sexual selection, and if sexual selection was a key piece of Darwin’s anti-slavery arguments, then it is puzzling why Darwin would have spent so much time discussing cases that did not really support his argument for the origin of human races, and it is also puzzling that his argument for the origin of human races would be so (atypically) poor.

Introduction

Reading Adrian Desmond and James Moore’s Darwin’s Sacred Cause: How a Hatred of Slavery Shaped Darwin’s Views on Human Evolution is like reading about someone vaguely familiar who existed in an alternate universe—a universe with humans at the center and pigeons, peacocks, and barnacles on the outskirts, instead of a universe with humans on the periphery. To make this case, Desmond and Moore seek to uncover the extent of Darwin’s anti-slavery motivations—in their words, the “moral passion firing his evolutionary work.”¹ Indeed, Desmond and Moore’s book amounts to no less than a call for a paradigm shift in the way we should think about Darwin—not as solely or even primarily motivated with explaining the facts of organisms in the natural world, but rather as being driven to provide the scientific underpinnings of the fight against slavery in the nineteenth century.² It is a testament to Desmond and Moore’s detailed examination of Darwin’s drafts, notes, marginalia, letters, and published works, just how successful they are at effecting that paradigm shift—no small feat given people’s entrenched views on Darwin. They exhaustively and convincingly show how, given Darwin’s anti-slavery family and colleagues, together with heated debates over slavery occurring in England and the U.S., Darwin was clearly participating in a larger conversation that led him to try to explain the origin of human races. To cite just one of their examples, they ask us to rethink why Darwin began the Origin of Species with an extensive discussion of pigeons. The pigeon discussion is often interpreted as Darwin showing that a species can be quite variable (as required for natural selection) or laying the groundwork for an analogy between artificial selection and natural selection. But Desmond and Moore point out that pigeons had already been explicitly cited in discussions on human races, and that a reader at the time would have understood what Darwin was really talking about.

According to Desmond and Moore, Darwin sought to defend the anti-slavery position by arguing that humans were all the same species, sharing a common ancestry, contrary to the claims of some other scientists who held that the different races were actually different species, each specially created. This echoed the sentiment of the anti-slavery medallion created by Darwin’s grandfather and displayed by Darwin’s family and friends, which read, “Am I not a man and a brother?” Of course, Darwin didn’t just argue that all humans had a common ancestor; he also argued that all organisms shared one, or at least a very few, common ancestors. Indeed, these two concerns often seemed to go together for Darwin, as reflected in his notebook B musings:

Animals whom we have made our slaves we do not like to consider our equals.—Do not slave holders wish to make the black man other kind? … if we choose to let conjecture run wild then animals our fellow brethern in pain, disease, death & suffering, & famine, our slaves in the most laborious works, our companions in our amusements. they may partake from our origin in one common ancestor; we may be all netted together (231-2).

I am quite convinced by Desmond and Moore’s suggestion that scholars have failed to appreciate the extent to which anti-slavery concerns motivated Darwin (which is not to say that I would go as far as Desmond and Moore, who imply that they were his primary motivations). I am also convinced that common descent played a key role in Darwin’s anti-slavery arguments.³ However, I am less convinced by Desmond and Moore’s claim that:

 … the Descent’s rationale was always human sexual selection, and that was being justified by evidence across the zoological spectrum. Darwin himself admitted wearily that it was a ‘gigantic subject.’ And it was all in aid of explaining the human races” (p. 365-6; emphasis added).

They contend that “Darwin would put his utmost into sexual selection because the subject intrigued him, no doubt, but also for a deeper reason: the theory vindicated his lifelong commitment to human brotherhood” (p. 360). Indeed, according to Desmond and Moore, “Darwin had focused overwhelmingly on sexual selection to prove that all people had descended from one stock … sexual selection as explaining man’s racial ancestry” is the “pièce de résistance” of the Descent of Man (p. 370; emphasis in original). Thus, on Desmond and Moore’s view, the primary reason for Darwin to discuss sexual selection is to explain the racial origins of humans,⁴ and sexual selection forms Darwin’s primary argument for different human races.

Unfortunately for Desmond and Moore, the anti-slavery-centered Darwin is all too similar to Darwin as traditionally pictured, in this respect: He is not very forthcoming on topics that are controversial, even to his closest friends and colleagues. Many of his statements are ambiguous. For example, according to Desmond and Moore, “He told Wallace that his ‘sole reason’ for tackling man was to prove that ‘sexual selection has played an important part in the promotion of races’” (p. 360). But does that mean that he tackled sexual selection in order to tackle man, or that he tackled man in order to tackle sexual selection? Desmond and Moore’s interpretation is further called into question when a bit more of Darwin’s March 1867 letter to Wallace is examined:

I had intended giving a chapter on man, in as much as many call him (not quite truly) an eminently domesticated animal; but I found the subject too large for a chapter. Nor shall I be capable of treating the subject well, & my sole reason for taking it up is that I am pretty well convinced that sexual selection has played an important part in the formation of races, & sexual selection has always been a subject which has interested me much (letter no. 5440).

Darwin’s admission that sexual selection had always been a subject that had interested him might mean that explaining the origin of human races was not his primary reason for discussing sexual selection, which is not to deny that it was a reason. However, seen in context, we can see that explaining the origin of human races was clearly not his sole reason.

To give two other brief examples: Desmond and Moore reveal that Darwin’s first use of the term “sexual selection” (although not the first appearance of the ideas behind sexual selection) seems to have been in his “scrap ruminations” on Knox’s Races of Man in March 1856, around the same time that he was working on his “Big Book” and writing to his correspondents to find out whether different races shared the same ideas of beauty (p. 282). This shows the undeniable interest that Darwin had in using sexual selection to explain the origin of human races, but again, does it mean that the reason for discussing sexual selection is to explain the origin of human races? Similarly, Desmond and Moore uncover Darwin’s note on Prichard’s Researches into the Physical History of Mankind, stating that ‘Man’s Sexual characters are like those of tufted Ducks’ (p. 284)—but this doesn’t say what would have been more of a smoking gun—that tufted duck characters are like those of man, which would have suggested that he was looking for non-human animal cases to support his arguments for humans. I find nuggets like these intriguing, and taking all of Desmond and Moore’s pieces of evidence together (as they should be taken to appreciate their arguments in full) they are very suggestive. Suggestive, but ambiguous.

Admittedly, some are less ambiguous than others. Indeed, perhaps the passage that is the most supportive of Desmond and Moore’s thesis is one that they do not cite; in February 1867, Darwin wrote to Wallace, “The reason of my being so much interested just at present about sexual selection is that I have almost resolved to publish a little essay on the Origin of Mankind, & I still strongly think … that sexual selection has been the main agent in forming the races of Man” (letter no. 5420).⁵ But I’m not trying to claim that Desmond and Moore are wrong in what they say about Darwin; I find it difficult to glean motivations from Darwin’s letters and other sources given how closely Darwin held his cards to his chest.

Instead, I wish to raise some puzzles which arise if we accept Desmond and Moore’s account of Darwin’s motivations. As Desmond and Moore note, Darwin ended Part 1 of the Descent by saying:

We have thus far been baffled in all our attempts to account for the differences between the races of man; but there remains one important agency, namely Sexual Selection, which appears to have acted as powerfully on man, as on many other animals … it can be shewn that it would be an inexplicable fact if man had not been modified by this agency, which has acted so powerfully on innumerable animals, both high and low in the scale. It can further be shewn that the differences between the races of man, as in colour, hairyness, form of features, &c., are of the nature which it might have been expected would have been acted on by sexual selection. But in order to treat this subject in a fitting manner, I have found it necessary to pass the whole animal kingdom in review; I have therefore devoted to it the Second Part of this work (vol. I, p. 249).

This passage seems to support Desmond and Moore’s reading of Darwin; Darwin seems to be saying that the whole reason for the extended treatment of non-human animals (ten chapters worth) in Part II of the Descent is to explain the differences between the human races. But Desmond and Moore tell us very little about how Darwin actually argued that sexual selection could explain the human races. They seem to suggest that female choice for aesthetic characters can straightforwardly explain the differences between human races if we think (as Darwin did) that those differences are “skin-deep” and “a matter of preference” (p. 373), but his arguments are not at all straightforward. I propose to look at Darwin’s fairly complex argument for the origin of human races in detail, something that (as far as I can tell) has not been done before, on the assumption that his published arguments are also relevant for understanding his motivations. Once we do, we will see that his argument is puzzling in a number of respects; not to put too fine a point on it, but it’s not a very good argument—by Darwin’s own standards. Namely, the way that Darwin explained sexual selection in non-human animals has a number of important differences from the way that he explained sexual selection in humans.⁶ Thus, it does not seem as though the discussion of non-human animals provides very good support for the case for human races. (In contrast, I think that Darwin’s arguments are generally excellent, and he makes a much better case for sexual selection in non-human animals).

I proceed by first discussing sexual selection in non-human animals: the phenomena that Darwin sought to explain and his sexual selection explanation itself. I then turn to sexual selection in humans and show how human sexual selection on Darwin’s account was different from most cases of sexual selection in non-humans. I then show that even the exceptional cases in non-human animals were handled differently from the human cases; Darwin offered reasons for why the exceptional non-human cases were exceptional, but offered no such reasons for humans, which is a bit puzzling if we accept Desmond and Moore’s view of things. Finally, I offer some concluding thoughts on the implications of these puzzles.