Jonathan R Smith
Dr Teri Potter
ANTH 1030
August 8, 2015
Bipedal and cranium evolution
The development of the Hominid line in the development in bimetallism and the increase in brain size. Over human evolution he sign of both have also been signified by great leaps in other areas. The fossil record shows varying lines and genetic signatures show how the lines from chimps have deviated from their common ancestor.
Bipedal locomotion is one of the greatest evolutionary events of human history. The very nature of Bipedal movement is distinct to Homo sapiens today, but could very well have occurred in many species. The ability to grasp and carry objects while walking, run to escape a predator, or to obtain resources, has set bipedal movement apart from other animals on the planet. A recent research study (Neither Chimpanzee not human) shows provide some insight into what they believe is the oldest found ancestor to modern humans, Ardipithecus. The study shows how the species shows the first signs of bipedal evolution with a development in a terrestrial niche in the woodland-to-forests that occupied Ethiopia and Kenya. They further use feature such as teeth and smaller canine teeth that are more similar to modern humans then some other hominids that live at or within the same time frame. “Ardipithecus was one of the few surviving lineages of the Miocene ape adaptive radiation: it preserved fundamental arboreal adaptations and it exclusively shares several independent character complexes with all later hominids.” This even grew into a debate within California Berkleys Athropology and Human Evolution Department, if to reclassify Hominids based on this feature, since this is an adaptation distinct to Humans within the Apes.
Though there is a growing view that what has traditionally been considered the evolutionary model of us evolving from a Chimp like quadrupedal Ape, to that of a possible semi-quadruped. The view is held on the distinct lack of fossils for Chimps and other great apes beyond 4.4 to 8.6 million years ago. The idea, though I am skeptical about, it is that a Forest dwelling Monkey became more terrestrial and that all Apes developed from this one species. This monkey due to its terrestrial nature began to become bipedal in motion resulting in the loss of its tail. A plausible scenario based on studies from capuchin monkeys, and the human locomotion that they acquire after long period of terrestrial dwelling and movement. This then led to two species that one became Gorillia and subsequent species that started populating dense forests. Populations then reconnected leading to Chimpanzees from Pre-Humans. The article that this came from didn’t seem very plausible to me at first. This was until reading an article from The New York Times about a genetics study done in 2006 by Broad University Mass. indicating a possibility of two splits using the fossil record and genetic analysis to support his claim. The splits he concluded would have occurred about 7 million years ago and 5.4 million years ago respectively. Then using the sudden explosion of plausibly bipedal hominid that occurred in the fossil record as evidence. Indicating the possibility that Bipedal locomotion could have begun far further in the past then previously thought. Since many varying species that lived within the same area and around the same period in time show signs of bipedal movement. I myself don’t have enough knowledge about all the hominid species to provide a good perspective. The theory though with current evidence with Neanderthals made me rethink what I knew. It shows that no single theory about the evolution of bipedal motion and human evolution is completely clear.
The evolution of bipedal walking has created some distinct patterns in species that seem to be common, even among none primates. A bowl shaped pelvis in hominids, the inline structure of the large toe within the foot (Both Hominids and Non-Hominids), the foramen magnum, the vertebrate column, Lengthening of the leg limbs the enlarged knee joint. The pelvis as a result to bipedal walking gait is that it widened and helping provide support for the up right structure. The transition of walking is not that different from Quadra pedal, the locomotion is very much the same. The increased size of the knee bone and seems to be the first step in the evolutionary chain in conjunction with the hip and thighbone more angled. This seems to start around 4 million years ago. At approximately 2.5 million year the spine begins to curve. Between 1.95 the hip support for the legs begins to appear leading to full bipedal movement.
These stages in evolution also had some effects on our brain size. The brain as we continue to improve technology or gather resourced has increase in size. Sahelanthropus tchadensis is the oldest known hominid or near hominid found the brain cc was about 350cc. One defining feature is the small teeth that it shares with later hominids similar to modern humans. Ardipithecus ramidus still had the brain size of that similar to chimpanzees, but showed features that more closely resemble later hominids. Australopithecus africanus is the first skulls that see the brain cc change to an average of 420 to 500cc. Australopithecus sediba is a strong candidate for the ancestor of Homo showing several human like traits in the skull. The volume of the single specimen found is 420cc and is that of a boy. Homo habilis shows a considerable increase in brain size from the contemporaries and previous hominids. From 500 to 800 cc one of the largest brain capacities of that period, along with the finding of stone tools. The bulge of the Broca’s area indicate that Homo habilis the possibility of speech. Though due to the large range of brain capacity there is debate on habilis and dividing it into separate species. Including one specimen (ER 1470 – Homo rudolfensis) that shows a less robust brow ridge seen in Homo erectus that could be reclassified based on a new species. Homo georgicus seems to be a likely candidate to bridge between Homo habilis and Homo erectus with a brain capacity of 600 to 780 cc shows a slight increase in height over other specimen. Homo Erectus existed between 1.8 and 300,000 years ago and had an average brain capacity of 1100 cc ranging from 750 to 1225cc. Homo sapiens (archaic, neanderthalensis and sapiens) all show an increased brain capacity from erectus. Archaic brain capacity is about 1200cc that is an increase fro erectus but has many features similar to erectus; one change that is noticeable is the less robust skeleton structure for Erectus. Neanderthalensis had a brain capacity of 1450cc that seems to correlate with the greater bulk of the species.
Sapiens or modern humans have a brain capacity of 1350cc. This seem to be a trait that is continuing today over the past 10,000 years and traits such as smaller teeth size and slowly fluctuating cranial capacity has occurred along with less robust bodies. Teeth size seems to be proportional to areas where food-processing techniques have been used the longest. Showing how even today we are evolving.
The changes that have occurred on the path of human evolution show how a species even today can evolve. The change and ability to walk upright and the changes physically required to do this. Hominid increase in larger cranial capacity as we migrate a crossed land out of the forest. This leading to us humanity as we continue to evolve.
Two splits between Human and Chimp lines Suggested, Nicholas Wade, New York Times May 18, 2006
Human Characteristics: Walking upright, Smithsonian, Smithsonian Magazine August 4, 2015
http://www.talkorigins.org/faqs/homs/species.html