I recently posted a systematic review of research on the dual mating strategy hypothesis, what AF/BB is loosely based on. It found that most research on the dual mating hypothesis has failed to replicate.

Research that also failed to replicate in this review involved findings that women preferred more dimorphic men, or shorter term sexual pairings, when women are most fertile. This was central assumption of the dual mating hypothesis.

Here is a recent study that tested this assumption in a randomized controlled trial. RCTs are the gold standard for generating causal scientific evidence. They are at the top of the evidence pyramid. We can't use this methodology often in psychology, but here is one example of when we can.

The methodology and results are succinct: women were given the hormone androstadienone to replicate fertility. Women did not have a preference for male sexually masculine or dimorphic faces in the hormone or placebo condition.

Analyses showed no preference shift towards masculinity in fertile compared to non-fertile phase of menstrual cycle, and no decrease in masculinity preference was found in hormonal contraceptive users as dual mating theory predicts.

An odor stimuli was also used: per the dual mating hypothesis and past research we should expect differential odor sensitivity during periods of fertility. (This has been explained as female preference for more masculine odors during fertility.) No difference in sensitivity to odors was found.

From the discussion:

Firstly, in current study we did not find preference shift regarding facial masculinity between menstrual cycle phases, despite using larger sample size than some of the earlier studies, which is in line with recent studies also reporting non-significant results (Jones et al., 2018; Marcinkowska et al., 2016, 2018).

Also, in current study no evidence was found that hormonal contraceptive use would decrease masculinity preference as group using hormonal contraceptives did not differ from normally ovulating groups regarding preference for facial masculinity.

The authors point out that previous research that has found effects, aside from not having been consistently replicated, did not find robust effects.

Secondly, in current study androstadienone did not affect attractivity evaluations depending on phase of menstrual cycle or use of hormonal contraceptives as dual mating strategy predicts. Earlier studies (Ferdenzi et al., 2016; Thorne et al., 2002) have also reported no clear effect between fertility and androstadienone, and to this date there is no clear evidence that androstadienones effects are dependent on fertility. Also, no main effect was found for androstadienone regarding facial attractiveness as we hypothesized, adding up to the findings of Hare et. al. (2017). In current study 30mg of androstadienone was used, which is larger amount than typically found in male axillae (Gower & Ruparelia, 1993), and its it unlikely that null findings are due to a weak signal.

Recently growing number of studies have failed to find support for dual mating strategy hypothesis. In current study no support for dual mating hypothesis was found, albeit two different signals of genetic quality were used, and a larger sample was collected. These findings are in line with recent studies, that have used within subject paradigm and larger sample sizes. In a comprehensive review Jones et. al (2019) have pointed out methodological problems in studies reporting significant results regarding dual mating strategy hypothesis, mainly low statistical power due small sample size and use of between subject -design. As the statistical power of earlier studies has been low, it is probable that significant results are due false positives which is supported by larger studies failing to replicate these earlier results (Jones et al., 2018; Jünger et al., 2018; Marcinkowska et al 2016, 2018; Stern et al., 2020). Thus, although dual mating strategy has been influential in human mating psychology it does not have strong empirical support.

Final thought here: evolutionary psychology has a bad reputation within psychology as a field with hypotheses that are difficult to test and results that don't replicate well. It looks like the dual mating hypothesis is turning out to be another theory that has become more influential than the evidence warrants.