Cilvēki dzīvo baros vienkārši tāpēc, ka naturāli vienīgās no primātiem homo sapiens sapiens mātītes nevar vienatnē piedzemdēt. Cena par staigāšanu uz divām ekstremitātēm un lielākām smadzenēm. Senākā profesija, dārgie draugi, ir nevis prostitūcija, bet vecmāšu profesija.

Because the human fetus emerges from the birth canal facing in the opposite direction from its mother, it is difficult for the mother, whatever her position, to reach down, as non-human primate mothers often do, to clear a breathing passage for the infant or to remove the umbilical cord from around its neck. If a human mother tries to assist in delivery by guiding the infant from the birth canal, she risks pulling it against the body's angle of flexion, possibly damaging the infant's spinal cord, brachial nerves and muscles. The human adaptation to this challenge is to seek assistance during birth. (..) In summary, modern human birth differs from modern non-human primate birth in three fundamental ways: (1) the neonatal head and body generally pass through a series of rotations during birth in response to the close correspondence between neonatal head and shoulder dimensions and maternal pelvic dimensions; (2) the neonate usually exits the birth canal in an occiput anterior position; and (3) human birth occurs in a social context with others in attendance.
/../ To put it in evolutionary terms, as bipedalism evolved, natural selection favoured the behaviour of seeking assistance during birth. /../The perspective of evolutionary medicine argues that the emotions of childbirth are among the human adaptations to the obstetric complications of bipedalism.

Ļoti kvalitatīvs mazs rakstiņš, bildes arī super:
http://onlinelibrary.wiley.com/doi/10.1046/j.1471-0528.2002.00010.x/full