As our ancestors began to stand upright we began to understand how evolution started to take different directions on the way to our current bodies and abilities. These early bipeds looked very little like us but also were a significant divergence from the chimps and apes. Clearly, the change in body stature requiring walking upright is far different than the bony skeleton and head position of the knuckle-walkers. It is interesting to note how the position of the skull and foramen magnum have lead researchers to determine bipedal ability with very limited fossilized remains. This simple difference begs us to search for links in our evolutionary chain that might include a similar pelvic girdle and secondary spinal curvatures more like modern humans. The change in foot bones associated with an opposable great toe do seem to indicate a major transition from life in the trees. Likewise, it seems the length of the upper extremities also was a change which occurred without a significant fossilized trail.
Hominin diversity is exemplified by the variations that occurred over time with respect to dentition. These potential ancestors must have experienced changes in diet which were sustained over many generations for teeth to develop which accommodated different methods of mastication. The decrease in canine size seems reasonable if these creatures did not require large teeth for biting for personal defense. As molars appeared in the fossil record, chewing foods seems to have lead to our current jaws and teeth. This seems as important a path to follow as the development of an upright stature when examining the transition to modern humans. The dental record from our distant ancestors to modern man is an interesting change when only considering the canine teeth. We still have canine teeth that differ in design from our incisors and molars, yet they serve no significant purpose for our everyday diet. Like a vestigial tail or our vermiform appendix, canine teeth seem to be a remnant from our ancestors in Africa.
Of all the remains discussed so far which took millions of years of time, none of the hominins had yet shown significant increases in brain volume. I find it interesting to consider that these bipeds spent so long on earth developing different body characteristics to accommodate their environment, climate, and food sources, yet larger brains incorporating greater abilities of reasoning had not been selected for as advantageous genetically. It seems as though a body undergoes natural selection primarily as an avenue for survival rather than a mechanism of advanced cerebral power. If all of the changes that we have discussed from class took 2-4 million years to occur, it is amazing that our brain size could have expanded over only a couple hundred thousand years.
Fossilized skeletal remains of our hominin ancestors offer snapshots in time of evolutionary changes leading to our current human design. These snapshots, when pieced together, can create the tree of diversity which began with our most distant hominin ancestor who left the trees for a life on the ground. The information that is gleaned from the fossil record not only provides information about our historic evolution, but may lead us to understand how our current environment might lead to changes in our future.