Male female twins have sex
Boy-Girl Twins: 5 Things Parents Need to Know
Feb 9, However, in some cases, relationships between twin siblings can go a bit far. In some cases, brothers or sisters can become so intimate that they become sexually intimate. In a way, it's as though they're having sex with themselves ( what with being identical and all). Keep reading to discover twins opening.
Incest between twins
Boy-Girl Twins: 5 Things Every Parent Needs to Know | Talk About Twins
Male twins reduce fitness of female co-twins in humans | PNAS
Description:Effect of producing same- versus mixed-sex twins on the mother's fitness, measured as the number of grandchildren produced by her offspring controlling for differing numbers of offspring raised to adulthood. Discussion There is increasing evidence that conditions experienced before birth can have profound effects on the subsequent growth, survival, and reproductive capacity of individuals 1 — 8. For example, the prenatal acquisition of hormones from developing neighbors in viviparous animals has been shown to have significant consequences for adult morphology, physiology, and behavior both in mammals 9 , 12 , including humans 11 , 13 — 20 , as well as in viviparous lizards An intriguing implication of such effects is that if, through sex-specific interactions among offspring, litter sex ratios influence offspring success in adulthood, this interaction will modify optimal offspring sex ratios for mothers However, so far, the fitness consequences of prebirth sex ratio for offspring and mothers are largely unknown for viviparous animals, and hence their fitness consequences for the mother cannot be incorporated into models of adaptive sex-ratio bias
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