Shizuyo Sutou
Molecular and paleontological dating indicates human appearance 6 million years ago. Early hominin fossils show that they were bipeds. Three salient characteristics distinguish humans from other primates: bipedality, practical nakedness, and the family reproductive unit. Once a hairless mutation was initially introduced, the three characteristics became separately inexplicable. All primates except humans can carry their babies without using their hands. A hairless mother would be forced to stand and walk upright to hold a baby. Her activities would be markedly limited. The male partner would have to collect food and carry it to her to keep their baby from starving; irresponsible and selfish males could not have left their offspring. The mother would have sexually accepted her partner at any time as a reward for food. Sexual relations irrespective of estrus cycles might have strengthened the pair bond. Consequently, hairless and upright pairs would have established strong families. Early hominins had the opposable hallux and remained as arboreal denizens. Climate changes probably forced them to terrestrial life, but the ground was full of danger and trees were indispensable for refuge and nesting. Consequently, archaic hominins had mosaic characteristics of the upper body adapted for arboreal life and the lower body for terrestrial life, for which a larger brain became advantageous. Alternative strategies became possible: development of a large pelvis with a big birth canal through which a baby with a big head could pass, or delivery of an immature baby, with rearing after birth. The former was physically incompatible with an upright posture, and structurally unfavorable for swift movement. The latter was unavailable to primates, the babies of which had to cling to the mother; upright hominins were able to hold the immature baby with hands and raise it after birth.
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