http://en.wikipedia.org/wiki/Obstetrical_dilemma
The obstetrical dilemma began when human ancestors started to evolve into a bipedal creature. Because humans are the only obligately bipedal primates, meaning their body shape requires them to only use two legs, major alterations had to be made to the shape of the female pelvis.[1] A number of structures in the body changed size, proportion, or location in order to accommodate bipedal locomotion and allow a person to stand upright and face forward. To help support the upper body, a number of structural changes were made to the pelvis. The ilial pelvic bone shifted forward and broadened, while the ischial pelvic bone shrank, narrowing the pelvic canal. These changes were occurring at the same time as humans were developing larger craniums. Therefore, in order to successfully undergo childbirth, the infant must be born earlier and earlier, thereby making the child increasingly developmentally premature.[4] The concept of the infant being born underdeveloped is called altriciality. Other ways of evolving to cope with bipedalism and larger craniums were also important such as neonatal rotation of the shoulders to allow the infant to fit through the canal, shorter gestation length which allows the infant to be born smaller, assistance with birth, and a malleable neonatal head which is softer and leaves the birth canal more easily.
what is their proof that we human ancestors started to evolve to bipedal creatures? Kasi the problem with evolution is they say 1 + 1 = 2. Then after a few years "mukha 3 yun answer ah..sige 1 + 2 = 3
They are not so sure.
From your link.
This change
seems to have evolved over time because this dilemma does not seem to pose a problem for our most recent relatives, non-human primates, who still manage to give birth with little difficulty.
Human ancestors
seemed to originally give birth in a similar way that non-human primates do. Most primates have neonatal heads that are close in size to the mother’s birth canal.
ito sa bipedalism
There are at least
twelve distinct hypotheses as to how and why bipedalism evolved in humans, and also some
debate as to when.
Recent studies of 4.4 million years old Ardipithecus ramidus suggest bipedalism, it is
thus possible that bipedalism evolved very early in homininae and was reduced in chimpanzee and gorilla when they became more specialized. According to Richard Dawkins in his book "The Ancestor's Tale", chimps and bonobos are descended from Australopithecus gracile type species while gorillas are descended from Paranthropus. These apes
may have once been bipedal, but then lost this ability when they were forced back into an arboreal habitat,
presumably by those australopithecines who eventually became us (see Homininae). Early homininaes such as Ardipithecus ramidus
may have possessed an arboreal type of bipedalism that later independently evolved towards knuckle-walking in chimpanzees and gorillas[48] and towards efficient walking and running in modern humans (see figure). It is also
proposed that one cause of Neanderthal extinction was a less efficient running.
