Eine Hypothese ist, dass bei verschiedengeschlechtlichen Zwillingen gegenseitige hormonelle Beeinflussungen auftreten können. Insbesondere wird vermutet, dass der höhere Testosteronspiegel des männlichen Zwillings den weiblichen Zwilling beeinflusst. Wenn der weibliche Zwilling einem höheren Testosteron ausgesetzt ist, dann könnte das in den passenden Monaten Auswirkungen haben. Es ist aber in diesem Bereich noch vieles unklar:
Die Wikipedia hat folgendes dazu:
Prenatal Testosterone Transfer also known as prenatal androgen transfer or prenatal hormone transfer refers to the phenomenon in which testosterone synthesized by a developing male fetus transfers to one or more developing fetuses within the womb and influences development. This typically results in the partial masculinization of specific aspects of female behavior, cognition, and morphology, though some studies have found that testosterone transfer can cause an exaggerated masculinization in males. There is strong evidence supporting the occurrence of prenatal testosterone transfer in rodents and other litter-bearing species, such as pigs. When it comes to humans, studies comparing dizygotic opposite-sex and same-sex twins suggest the phenomenon may occur, though the results of these studies are often inconsistent.
Der Mechanismus wird dort wie folgt dargestellt:
Testosterone is a steroid hormone; therefore it has the ability to diffuse through the amniotic fluid between fetuses. In addition, hormones can transfer among fetuses through the mother’s bloodstream
Eine Studie dazu:
In this paper we review the evidence that fetuses gestated with a male co-twin are masculinized in development, perhaps due to the influence of prenatal androgens: the so-called twin testosterone transfer (TTT) hypothesis. Evidence from studies of behavioral, perceptual, cognitive, morphological and physiological traits in same- and opposite-sex human twins is considered. Apart from two studies reporting increases in aspects of sensation-seeking for females with a male rather than a female co-twin, there is sparse evidence supporting the TTT hypothesis in behavioral studies. Outcomes from studies of perception (in particular otoacoustic emissions) and cognition (in particular vocabulary acquisition and visuo-spatial ability) provide more consistent evidence in support of masculinized performance in twins with a male co-twin compared to twins with a female co-twin. The outcomes favorable to the TTT hypothesis for otoacoustic emissions and visuo-spatial ability are restricted to females. Studies of physiology and morphology (e.g., brain volume, tooth size and 2D:4D ratio) also show some influence of co-twin sex, but again these effects are often restricted to female twins. Because females produce little endogenous testosterone, the effects of gestation with a male co-twin may be more pronounced in females than males. Thus, while uneven, the evidence for the TTT hypothesis is sufficient to warrant further investigation, ideally using large samples of same- and opposite-sex twins, along with control groups of same- and opposite-sex siblings when the characteristics assessed are potentially open to social influences.
► Hormones can transfer between fetuses in animals affecting phenotypic development. ► The existence of a similar mechanism in humans remains uncertain. ► A review finds little evidence for masculinization of behavior due to testosterone transfer. ► Some evidence consistent with transfer for perception, cognition and physiology. ► Evidence of masculinization is typically restricted to females with a male co-twin.
Quelle: Evaluating the twin testosterone transfer hypothesis: A review of the empirical evidence
Hier ist also noch vieles unklar. Es scheint einige Hinweise zu geben, dass der Mechanismus auch bei Menschen greift, aber es ist hier wohl weitere Forschung abzuwarten.