In this unit, we have learned many ancient relatives of Homo sapiens. There is a large tree of human evolution, and the tree has many branches. The names are quite complicated and confusing, such as Ardipithecus, Australopithecines, Australopithecus afarensis, and so forth. I have found an image online to describe the relationships of these names. The large tree has been divided into several groups, including the Ardipithecus group, about five million years ago, the Australopithecus group, about three million years ago, the Paranthropus group, about two million years ago and the Homo group. Of course, we belong to the homo group.

The Ardipithecus group is believed to be the earliest humans, and the closest link to the other primates. They evolved in Africa, and the major characteristics of them is to walk upright. In this group, there are names like Sahelanthropus tchadensis, Orroin tugenensis, Ardipithecus kadabba, and Ardipithecus ramidus. The Australopithecus group includes names like Australopithecus anamensis, Australopithecus afarensis, Australopithecus garhi, and Australopithecus africanus. The Paranthropus group has very large teeth and powerful jaws, which enabled them to feed on a variety of foods. In this group, there are names like Paranthropus aethiopicus, Paranthropus boisei, and Paranthropus robustus. At last, it is the Homo group, and the other members in this group are quite like modern humans, compared with the members of other groups, and these names include Homo habilis, Homo erectus, Homo florsiensis, Homo neanderthalesis, and Homo sapiens, and I think these parts will be covered in the next unit. The tree is quite clear and useful, it could be found here: http://humanorigins.si.edu/evidence/human-family-tree

For some hominin traits that can inform us about modern human biology, firstly, I think it should be walking upright. It is like the first step away from the other primates living in the forests. In the process of evolution, ancient homos have the ability to walk upright, and their increased flexibility helped them to adapt to various environments. As introduced in our course, the earliest evidence is found in Sahelanthropous about six million years ago. Gradually, we have stronger knees and a spinal with more suitable shape, as well as different toes, pointing in one direction. Walking upright has freed the hands, so that the hands could create tools, collect food and pick fruits, and even create more complicated culture in later days. In one website, I found that there are also costs for walking upright. Modern humans often have back pain and other skeletal problems, and these could be treated as a side effect of walking upright, because the weight has to be distributed only on two limbs. (humanorigins.si.edu)

Another trait I think worthy mentioning is the increase of brain size. We now regarded ourselves as the most intellectual being in the world, and I think the brain is the most important contributor to our intelligence. Gradually, the brain size increased. We gradually had a larger and more complex brain, which is essential for the surviving of our ancestors, and I think it is also essential to the diversified and rich cultures we have created. Interestingly, there are also costs for a larger brain, including its large consumption of energy. The brain is 2% of our body weight, but it consumes more than 20% of the oxygen supply and more than 20% of our blood flow. Also, larger brain also means larger head, and it would bring more pains and dangers for the child birth process, especially in the ancient times. (humanorigins.si.edu)

References

Human Family Tree. Retrieved from http://humanorigins.si.edu/evidence/human-family-tree

Humanorigins.si.edu. Walking Upright. Retrieved from http://humanorigins.si.edu/human-characteristics/walking-upright

Humanorigins.si.edu. Brains. Retrieved from http://humanorigins.si.edu/human-characteristics/brains