52. Handsome Men, Lousy Semen: 4. The Phenotype-Linked Fertility Hypothesis

I have been discussing Soler et al’s 2014 article in the Journal of Evolutionary Biology or, more specifically, the press release that accompanied that article [see 49].  Soler et al found that men considered attractive had better quality semen whereas men deemed more masculine did not.

Once I start burrowing down on something it is hard for me to move on (hence the bazillion loose ends in this blog).  And I did become a bit fascinated with Soler et al’s study.  It left me wondering: What possible rationale would lead someone to measure semen quality and men’s appearance?  Why even ask the question?

Now, there is nothing wrong with conducting preliminary or exploratory research without any preconceived notion of what you may find.  That is, it is quite acceptable to answer “Why not?” and “I don’t know” to the questions of “Why ask the question?” and “What does it matter?” In fact, much of science has been built around people merely being curious about why things are or how they work. Most initial discoveries were made by people who would now be considered amateurs or laypeople (those who had no direct affiliation to an university or were not compensated for their scientific work).

However, things have changed.  Science is now a paid profession and practiced exclusively (more or less) by members of a specific guild.  As a consequence, it is difficult to conduct and publish research without either funding or ethics clearance.  And to get that funding or clearance, you must first outline the method of your study (how you will gather your data) and provide answers to the questions of rationale and relevance.

So, what is the theory behind Soler et al’s research?  What is the rationale that connects male facial attractiveness with quality of semen?  The rationale, it would appear, is based on promiscuous birds.

Let me explain.

Soler et al begin their article with two possible explanations of why women might prefer attractive men.  One possibility is that facial traits (attractiveness) may provide cues to other beneficial features such as intelligence or health and females may prefer attractive men in order to pass these desirable traits to their children.

[A lot of ink has been spilled over arguments about the relationship between beauty and intelligence (as well as race).  Even if we leave out the virtual impossibility of constructing any culture-free method of assessing global intelligence or beauty and ignore the mountains of data and argument over the inherent biases created through the process of social stereotyping, the correlation between intelligence and beauty is, at best, modest.  If beauty does serves to genetically select intelligence, then it is doing a spectacularly bad job of it.]

In contrast to a genetic benefit, females may also choose attractive men because attractive men may be more virile.  According to Soler et al, support for the relationship between attractiveness and fertility can be found in the phenotype-linked fertility hypothesis.

Here come the promiscuous birds.

The phenotype-linked fertility hypothesis was coined by Sheldon in 1994.  In his speculative article, Sheldon was trying to explain why female birds, after forming a pair-bond, would continue to seek out mating opportunities with other males.  Among birds it had previously been assumed that social monogamy equalled sexual monogamy. We know now that genetic monogamy (evidence of one mate) among socially monogamous bird species is more the exception than the rule. The phenomenon of extra-pair paternity represents an important and relatively recent discovery in avian research.

Sheldon posed that mating outside the social monogamous bond increased the likelihood of successful egg fertilization and those males from which females sought extra-pair paternity possessed features or phenotypes that suggested higher fertility.  Hence the label: phenotype-linked fertility hypothesis. Formally defined, a phenotype is features of an organism that we can observe.  Your phenotype — what you look like — is derived from your genetic makeup as well as environmental influences.

Sheldon was very clear on two points.  First, he did not feel that extra-pair paternity was driven by birds attempting to pass genetic benefit to their young.  That is, extra-pair males were not selected for reasons of fitness (genetic improvement) but more for the purpose of enhanced fertility.  Second, Sheldon acknowledged that empirical evidence in support of his hypothesis was not yet abundant.  However, he did provide a number of possible directions for future research.

Sheldon’s main reason for rejecting genetic improvement or fitness as the rationale underpinning extra-pair paternity was based on classic evolutionary theory, specifically Fisher’s fundamental theorem of natural selection.

And what is Fisher’s fundamental theorem of natural selection, you ask?

Well, I am glad you asked because that is where I am heading in the next few posts.

52. Tarsus