From my memory, these are other reasons to stand up found in the animal kingdom . . . . Courting ritual (unlikely, doggystyle?)
Face-to-face copulation is extremely rare. I can't think of any other mammal that can do it. (Although I don't know anything about the fully or nearly aquatic mammals like dolphins and sea lions.) Humans have the capability because of two unique anatomical distinctions:
- Our wide pelvis. It allows all the legs and other body parts to fit comfortably into the crowded space. This evolved as our brains enlarged, to fit the baby's cranium through the birth canal. As it is, our babies are born at a much lower level of brain development than other mammals, they are more helpless for a longer period of time, and their heads continue growing longer after birth. Ardipithecus, with a brain less than half the size of ours, did not have such a wide pelvis.
- And of course the bipedal stance. A couple of key muscles have been rerouted to make it easy to lock our knees, most famously the gluteus maximus which gives our butt its characteristic dual-hemisphere shape. This also makes it possible to lie down with our legs fully horizontal and fully straightened, without which face-to-face copulation would be awkward and uncomfortable.
The Discovery Channel is kid-friendly and completely avoided the subject of mating, so I don't know whether Ardipithecus was far enough along in these transitions to facilitate the "missionary position."
From my scanning of academic sources on the topic, there were early hominids that had evolved efficient bipedal walking and were not considered quadrupeds.
Presumably scholars are working overtime to overhaul those written records, now that Ardipithecus has given us an almost entirely new look at the early history of hominids. Such as pushing our branching off from the other Great Apes back two million years and tossing the Savannah Hypothesis into the dustbin.
The fossil was first discovered in the 1990s but it took more than a decade--and lots of computing power--to assemble and correlate it. But that computing power also gives us a better reconstruction of her musculature, from the geometry of the ligament attachment points on the bones, and from real-time 3-D simulations of the inertial shifts generated by walking and other movements.
The two-hour TV special was certainly spellbinding. Paleontologists, primatologists, physicists, those folks who figure out with amazing accuracy what your missing eight-year-old looks like at sixteen, and a guy whose profession is the reconstruction of hominids and other animals from all of this information, gave us a one-minute animation of Ardipithecus walking through the forest, showing the movements of the muscles, the balancing, and the way the upper body moved in response to all of this.
I regard a certain ‘water-based hypothesis’ of hominid evolution to be pseudoscience.
It does seem that way now that we have incontrovertible evidence of a transitional species (the "Missing Link") that was an erect-walking forest-dweller but retained the ability to climb trees almost as well as a chimpanzee in an emergency.
But I wouldn't have been so quick to discard the Aquatic Ape Hypothesis last year. I'm still waiting for answers to two questions:
- Why are we the only apes with these (seemingly) vestigial little webs between our fingers?
- Why are we the only apes buoyant enough to permit the integration of long periods of swimming into our normal daily routine?