Blog Five: Human Evolution

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.

4 thoughts on “Blog Five: Human Evolution

  1. I agree that there could be clues as to where our evolution is headed from studying the remains of our ancestors. Much of science is geared towards making reliable predictions. As Bill Nye said, natural laws work the same now as they always did. A lot of what is happening with species currently, like antibiotic resistance in bacteria and pesticide resistance in insects, could be predicted by natural selection. I do think we may diverge from earlier species though.

    The reason for that is that we have far more control over our change and development than previous species. We can change our own environment, through our actions and our development of technology. With all the GMOs out there, I do wonder if we are headed towards human genetic engineering in the near future. I do not think that is necessarily a bad thing, either. We might be able to avoid some of the nastier parts of natural evolution, like how our evolution towards bipedalism made childbirth difficult. I do find the idea somewhat troubling though, as people make decisions to have “designer babies” that have traits not selected for survival or comfort.

  2. I also thought it was very interesting that bipedalism isn’t correlated with large brain size. It was surprising to me because I thought that it would have been the other way around. Species would get smarter and then realize it was better to walk on two feet. However, this was definitely not the case. Many bipedal species had brains on the smaller size, and because of this most of them did not survive. I also wrote about dental patterns in my blog this week. It’s one of the best ways, I think, to differentiate between different species and learn important things about that species, like what kinds of foods they probably ate. I also think it’s pretty interesting that we still have canine teeth, despite no real use for them. This goes to show that just because we don’t have use for a trait, doesn’t mean it’ll disappear with evolution.

  3. Your post was very interesting. You made a lot of good points. One in particular that stuck with me is “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. ” This is so true, I’ve never thought about this in this light. It’s weird that the hominins body physically changed based on evolution but no increases in brain volume. Fossil remains helps us get a glimpsed of our past, but you’re right, it also will help us to understand how our current environment will lead to changes in our future.

  4. I really enjoyed your post! I also think it’s really interesting how scientists can determine bipedalism by looking at the foramen magnum in the skull. You also mentioned how feet and the length of the extremities were key indicators; which I would like to extend to the hands themselves. Another way to distinguish “knuckle-walkers” from bipeds is by actually looking at the knuckles. It is incredibly strenuous on the bones to bear so much weight, so when hominids evolved to rely less on their hands and more on their feet, the bones in their hands became more delicate (Note that this would most likely much more difficult to differentiate due the fact that there are multiple bones instead of just one). However, this subtle difference is yet another method scientists can use to determine bipedalism and therefor create a more detailed picture of where we came from.

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