As a bearded man, this has to be one of my favorite just-so stories. In Descent of Man, Darwin spoke quite a bit about the beard, and the different races/ethnies and the distribution of beards in them. Darwin (1871: 581) wrote:
On the other hand, bearded races admire and greatly value their beards ; among the Anglo-Saxons every part of the body had a recognised value … [also writing on pg 603] … for we know that with savages, the men of the beardless races take infinite pains in eradicating every hair from their faces as something odious, whilst the men of the bearded races feel the greatest pride in their beards.
Any man who has grown a beard admires and greatly values their beard. Darwin noted that beards were scant in Asian and Native American populations, as well as in Africa.
“Darwin specifically cited the human beard as a response to sexual selection serving mate attraction.” [Psychology Today, Beauty and the Beard]
Now, going off of this, we have this just-so story.
Men with the best beards attracted the most mates. Men who attracted the most mates had the most children. Men who had the most children had the best beards therefore, “beard genes” were naturally selected and eventually became fixated in males.
This has to be my favorite just-so story.
The New Republic almost word-for-word states my just-so story provided above:
Over the millennia, the theory goes, beardedmen were more successful in procreation than their smoother competitors, and the human beardevolved into its present form.
With so many so-called adaptations and things serving as “mate attractors”, how can selection “know” which trait to “act on”? This shows the ridiculousness of the just-so storytellers main weapon: reverse engineering.
Reverse engineering is “the inference from function to cause” (Richardson, 2007: 51). So they take the function (beards are seen as attractive to women) and then infer the cause (men with the best, most attractive beards were selected by women and thus “beard genes” became fixated in males since the best beards were fitness signallers to women since they found them attractive). But there is a flaw with reverse engineering: when accounting for such “design” in nature, in terms of adaptation, it can lead to just-so storytelling. AKA ad hoc hypotheses that explain what they purport to explain and only what they purport to explain.
Reverse engineering uses the design feature (beards) then extrapolate backward to presume its function (men with beards were seen as more attractive and thus, ‘beard genes’ became fixated since that’s what women found attractive). Reverse engineering can be used to make any story sound coherent; they necessarily conform with the data. Indeed, as Smith (2016: 279; emphasis mine) writes:
An important weakness in the use of narratives for scientific purposes is that the ending is known before the narrative is constructed. Merton42 pointed out that a “disarming characteristic” of ex post facto explanations is that they are always consistent with the observations because they are selected to be so.
This is why it’s problematic to accept this type of storytelling: they are consistent with the observations because they are crafted that way, but there is no observation that would increase the probability of the hypothesis being true so it’s just storytelling. In lieu of a time machine, we cannot verify these types of stories.
So we notice that beards (obviously) exist. Then we work backward and infer the function from the already-known outcome (as seen above). We then create the story that they were seen as attractive to women, thus they have been selected by women since they make for a more attractive mate. That a hypothesis conforms with the observation is not evidence that the hypothesis in question is true.
Research exists that men with beards are seen as more formidable mates for long-term relationships (Dixson et al, 2016). Mcintosh et al (2017) reported that “Women preferred full beards over clean-shaven faces and masculinised over feminised faces.” However, there is data that men with beards are perceived as more dominant but are not seen as more attractive than clean-shaven faces (Muscarella and Cunningham, 1996; Neave and Shields, 2008) Though evidence for current adaptiveness is not evidence for evolutionary adaptiveness. The fact that X is adaptive today is not evidence that X was adaptive in the human OEE (original evolutionary environment). This again goes back to reverse engineering. Attempting to account for design in nature amounts to nothing but storytelling since the hypotheses are inherently ad hoc. Evolutionary functional analysis most definitely leads to just-so storytelling, and the story of how and why men have beards falls prey to this as well.
Men’s beards may be the result of women’s choice, as X may be the reason for Y, but without a way to independently verify the hypothesis in question, it is then a just-so story. No, showing that women find men with beards to be better long-term partners is not evidence that female choice in the OEE (or in any point in evolutionary history) is evidence for the claim that beards became fixated in males due to female choice—sexual selection.
The problem with adaptationist explanations is that other modes of evolution are disregarded (nevermind the fact that the supposed mode of adaptation is supposed to be natural selection for the specific fitness-enhancing trait which cannot occur since NS has no mind and there are no laws of selection for trait fixation; Fodor, 2008; Fodor and Piatteli-Palmarini, 2010; also see Replies to Our Critics) such as drift, mutation, and migration (see Gould and Lewontin, 1979; also see Simon, 2018 for other critiques of EP hypotheses, namely that they are not testable).
In sum, the story that beards were sexually selected-for by women due to X (no matter what X is, be it attractiveness, dominance, etc) is a just-so story. It cannot be independently verified. Yes, beards are seen as status symbols and there is a considerable amount of research on men’s beards and what women think they mean today, but, again, that X is adaptive today is not evidence that X was adaptive in an evolutionary context. Simplicity, coherence, and fruitfulness are no reasons to believe a hypothesis (Smith, 2016); the hypothesis must be independently testable but there is no way to test this hypothesis—or any other—that trait X (beards, in this case) moved to fixation in virtue of its effect on reproductive fitness, therefore it is a just-so story.