Bipedalism, childhood, and ritualisation of human sexual behaviour: A hominin model scenario of ontogenetic selection

In this paper, the term childhood denotes the ontogenetic developmental stage of weaned mammal infants who are still helpless and need to be nurtured and protected for survival. Human infants have a pronounced childhood phase in contrast to great apes. For a hominin model scenario proposed here, it will be argued that upright bipedal locomotion facilitated early weaning and, as a consequence, the emergence of childhood. To raise their infants to healthy maturity by preventing early pregnancy after weaning, females exploited a succession of contraceptive traits, from concealed oestrus and adipose breasts to menopause. In turn, to ensure a sufficient reproduction rate of their own genes, males developed several related counter measures, from sexual objectification of female bodies as permanent mating targets, to altered male mental filters, then recognising young mature females as being beautiful and sexually attractive. In response to stuffed dry breasts that, to avoid mating, imitated breastfeeding and lactational amenorrhea, males could regularly verify milk secretion by inspecting breasts and nipples visually, manually and orally before copulation. When later such inspections lost their original fertility relevance, these activities may regionally have evolved into symbolic courtship habits, similar to ritualisation in the behaviour of waterfowls that had been investigated previously by Julian Huxley and Konrad Lorenz. Along this causal chain, contemporary sexual conflicts may - in part - have ultimately originated from initial hominin bipedalism.