Hello, sister mine! It's been rather long since I've posted, and for that I apologize. I've been meaning to bust out an epic piece on the subject of early humans, to incorporate some of the fragmented bits of hypotheses that have been floatin' around in my mind as of late. I'm super excited because I've finally stumbled across the perfect article to tie it all together!
National Geographic published
this article back in '06, entitled "Dikka Baby." It's about a fossil discovery made by an Ethiopian scientist, Zeresenay Alemseged, in Africa's Great Rift Valley (a place where a goodly number of hominin fossils have been found -- our early ancestors liked to hang out there, as it's a well-sheltered and fertile river valley. And, luckily for us future folk, tends to preserve remains quite nicely). What's totally spectacular about this fossil is that it consists of a nearly complete Australopithecus afarensis skeleton -- that of a three year old child, dubbed the Dikka baby.
A. afarensis was one of our very early ancestors, and lived more than three MILLION years ago. I know you're somewhat familiar with H. habilis and H. erectus on, so here's a handy timeline for reference:
The most famous example we have of A. afarensis is
"Lucy," a partial skeleton found in 1974. Much of what we know about this species comes from the largely (somewhat dubiously) reconstructed parts of Lucy's skull and body, so having a complete skeleton is fantastic. Also, Lucy was an adult when she died, so with the Dikka baby we have some insight into what this species was like as a child.
What's particularly special about this stage in human evolution is that it marks a transition into one of our most distinct trademarks: a relatively long span of time between birth and self-sufficiency, known as the infant-dependency period.
For some background:
Primates have some of the longest infant-dependency periods of all mammals, and among primates, humans have the longest. There are a few likely reasons for this; the foremost being our large brains. We actually can't stay in our mothers' wombs for long enough for our brains to completely develop, because if we did our heads would be too big to fit through the birth canal! So instead of coming out all chop-chop-ready-to-go like a baby deer, we have this period following birth in which we are totally dependent upon our mothers and the larger group so that we can mature to the point that some animals are just born at.
The Dikka baby's brain case (yes, that is a scientific term for the skull) is not quite modern human- sized, but still rather larger than a chimp's. This is indicative of a prolonged childhood. Now, this is where things start to get interesting. A. afarensis was bipedal, meaning they walked on two feet. While their upper bodies were still fairly ape-like, their hips and spine were positioned to allow upright walking, and instead of the grasping toes of their cousins, they had flatter feet and shorter toes to help propel the body forward in a walking motion. Without grasping feet, a baby can't cling to her mother like a chimp, and so has to be carried. This would have inhibited the mother's ability to provide for herself, and in turn caused her to depend more upon the larger group than her earlier ancestors would have. This dependency served to strengthen family bonds, and is the predecessor to the family structure that we modern humans identify by.
Now, the reason for which humans developed bipedalism has been the subject of great speculation among anthropologists. Some say it was to allow endurance; it expends less energy than "knuckle-walking," and while we can't move as fast as our knuckle-walking ancestors, we can go for longer distances. Some say a higher vantage point was beneficial in the sub-Saharan grasslands where we originated. All agree that freeing up our hands to be able to carry things was a really great idea. But to carry what? What could be so important for us to be able to carry that our entire physiology would rearrange itself in order to accommodate? Well, babies of course. But if you think about the way evolution works, this theory doesn't make much sense. People have to reproduce in order to have babies to carry, and if they're surviving long enough to have babies then obviously their physiology isn't going to have much incentive to change. However, try thinking about it like this: what if the
only babies who are surviving are the ones whose
mothers are able to carry them? These mothers must have the inclination towards bipedalism in order to do so, and therefore their progeny are going to have a higher chance than the last generation to carry this mutation as well. So in this way, the traits that allow bipedal walking have the advantage; it's like evolution in reverse!
Of course, no anthropological study is complete without input from the linguists. And they have hypothesized this big-brain-induced lengthy dependency period actually prompted the development of speech itself! Think about the way a mother coos and comforts her baby, and the way the baby makes noises in response. Combined with the group dependency I mentioned earlier, this could very well be where the forms of communication that led to speech really got started! I'm very interested in what you think of this model, as well.
The point all of this leads up to is really quite profound; that the very logistics of having a physically large brain are responsible for such staple human characteristics as bipedalism, social bonds, and speech, rather than our intelligence per se. It opens up the possibility of our earlier ancestors being much much smarter than we have assumed. All that was needed was the ability to pass on information, and the mental incentive to actually
share knowledge with our peers, to point us in the direction that led to where we are today.
