Does the Mother or Father Determine the Offspring Sex Ratio? Investigating the Relationship between Maternal Digit Ratio and Offspring Sex Ratio

Abstract

ObjectiveIn mammals, high parental testosterone levels present around the time of conception are thought to skew offspring sex ratio toward sons. The second to fourth digit ratio (digit ratio) is now widely accepted as a negative correlate of prenatal testosterone. Thus, we investigated the association between digit ratio and offspring sex ratio.MethodsA total of 508 Korean patients (257 males and 251 females) less than 60 years old who had one or more offspring were prospectively enrolled. The lengths of the 2nd and 4th digits of the right hand were measured by a single investigator using a digital vernier calliper. Next, the patients’ lifetime offspring birth sex ratios were investigated.ResultsMaternal (rather than paternal) digit ratio was significantly associated with the number of sons (r = -0.153, p = 0.015), number of daughters (r = 0.130, p = 0.039), and offspring sex ratio (r = -0.171, p = 0.007). And, the maternal digit ratio was a significant factor for predicting offspring sex ratio (B = -1.620, p = 0.008) on multiple linear regression analysis. The female patients with a lower digit ratio (< 0.95) were found to have a higher offspring sex ratio (0.609 versus 0.521, p = 0.046) compared to those with a higher digit ratio (≥ 0.95). Furthermore, females in the low digit ratio group have a probability 1.138 greater of having sons than females in the high digit ratio group.ConclusionsMaternal digit ratio was negatively associated with offspring sex ratio. Females with a lower digit ratio were more likely to have more male offspring compared to those with a higher digit ratio. Thus, our results suggest that the sex of offspring might be more influenced by maternal rather than paternal factors.

Polyunsaturated fatty acids influence offspring sex ratio in cows

“…Two main research lines have attempted to explain possible mechanisms involved [3]. The first is based on the finding that more dominant mothers produce more male offspring, possibly mediated via alterations in their testosterone levels [4]. The second has investigated associations between the body condition or diet of the mother and offspring sex.…”

Experimental and Self‐reported Measures of Risk Taking and Digit Ratio (2d:4d): Evidence From a Large, Systematic Study

“…Note, for example, the evidence that fetal and maternal testosterone levels are positively correlated(Gitau et al, 2005; but see alsoRodeck et al, 1985) and the evidence of a negative correlation between a mother's digit ratio and the likelihood of having a son(Kim et al, 2015).…”

Family effects on the digit ratio (2D:4D): The role of the interbirth interval

“…These discrepancies could be attributed partially to differences in methodology, especially the ways of grouping subjects (categories of birth order, sexual orientation groups, and so on) in different studies. Another possibility is that, most probably, the recorded effects are not caused solely by interactions between siblings themselves (through their mother at the individual level) but also (at the population level) by nonrandom relationships of digit ratio with sex ratio in progeny––the tendency of females with low 2D:4D ratio to give birth to more sons (Kim, Oh, Kim, Yoon, & Kim, ; Manning, Martin, Trivers, & Soler, ; Ventura et al, ), in connection to inheritance of digit ratio and possible positive assortment in 2D:4D ratio in parents (Manning, ). However, our results regarding the effect of SR in sibship on digit ratio were in disagreement with this prediction: more sex‐typical 2D:4D ratios were found in children from mixed sibships, while in one‐sex siblings the 2D:4D ratios were less sex‐typical.…”