Jeremy Solomon
imabum14@gmail.com
Saturday, April 2, 2011
I'll Be a Monkey's Uncle
A major theme of the book is how two seemingly different organisms are related. In most cases, Shubin takes the less-developed organism's features and explains how the organism evolved into an entirely different one. This process doesn't apply to the relationship between humans and apes (our closest relatives) with whom we co-evolved from a single common ancestor. If the "missing link" were to be found, what features would scientists use to prove its relatedness to both humans and apes? What does this say about the differences between humans and apes, in terms of which adaptations each species developed, and how the split occured?
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To start off, the theory of evolution is still debated. With individuals believing in creation, it is hard to tell what the “missing link” is because it is still a controversial topic. However, if evolution was true in humans, and there was a “missing link”, many body structures would be used to show the comparison. In humans, 46 chromosomes are in somatic cells whereas in apes, 48 chromosomes are in somatic cells. As discussed by Dennis O’Neil in his website, chromosomes 12 and 13 of the Ape’s genetic composition “seem” as though they would be chromosome 2 of humans if they were to be fused together. As seen on phylointelligence.org, chromosome 2 of humans (band patterns) is very identical to the fusion of chromosome 2p (chromosome 13) and 2q (chromosome 12) or chimpanzees. If scientists could somehow prove the fusion of chromosomes 12 and 13 in chimpanzees, then scientists would be able to prove the relationship between humans and apes.
ReplyDeleteWith the difference in chromosomes, different types of bodies were formed. For example, humans are animals that engage in a type of motion called bipedalism. Thus, our arms are smaller and weaker than our legs, and we thus walk upright on two feet. To complement our bipedalism, the pelvis has become “broader and more bowl shaped” (O’Neil). Thus, we are able to have a more erect body. At the split of apes and humans, a more upright organism which could walk on two legs was formed. This may have been because of a selective advantage. One selective advantage of this evolution would be the ability to walk and run in a more stable manner.
The ability to walk and run in a more stable manner also ties in with the structure of the foot. In primates, a more curled foot is present. As said in Campbell, “the earliest known primates were tree-dwellers, and many of the characteristics of primates are adaptations to the demands of living in the trees” (723). Thus, the foot was curled in early primates because it allowed for easier living within the trees. The curled foot allowed for “hanging” in trees and a more firm grip to stay within the tree without falling. Humans on the other hand have a more flat foot incapable of grasping objects to hang from. This evolution ties in with the ability to walk and run in a more stable manner. The flatter foot evolved from primates in order to allow for land living primates to live a more suitable life with an easier mode of locomotion. In simpler terms, by having the flat feet, the land primates were able to live and walk on land other that stay within the trees. Thus, bipedalism was created as a result of the flat foot because it allowed for a more efficient way to take advantage of the flat foot. Thus, the split of primates occurred because of the change in habitats from tree-living to more land-living primates. It was not a disadvantage to be a tree-living primate; however, it is an advantage to have a flat foot and be a land living primate because of the increased stability in motion.
Sources:
Campbell
http://phylointelligence.org/genetics.html
http://anthro.palomar.edu/primate/prim_8.htm (O’Neil)
Shreeraj Patel
shreeraj.patel1@gmail.com
The following response has been divided in order to meet character requirements
ReplyDeleteAs Shreeraj explained, differences in the chromosomes of humans and apes caused there to be a difference in the body types formed. More specifically, it is the type of genes that are expressed that lead to differences amongst members of a species. Differences in the amount of chromosomes of an animal might cause the proteins that are translated to cooperate differently resulting in differing phenotypes. However, this too is determined by which genes on the differing chromosomes are expressed. This is known as variation amongst a society. Following Darwin’s theory of evolution, this genotypic variation results in differing phenotypes or traits. The phenotypes each result in either a more advantageous way to access resources or a less advantageous way. This is known as natural selection. Those with the more advantageous traits will continue to reproduce at a more successful trait than those that lack it. This weeds out those that lack the trait until all members of the species possess and have therefore evolved (1).
An interesting difference between us and apes that Shreeraj pointed out is bipedalism. Given what we know about evolution and natural selection, the ability to stand up and walk on two feet must have provided humans an advantage that apes didn’t receive. Shreeraj mentioned that a possibility this occurred could have been to allow humans a more stable way to walk and run. There are many other possibilities this development occurred. One is that it was too hot near the ground (2). Another is that it used less energy that walking on four legs (3). Another still theorizes that it was to allow for the formation of a bigger brain (4). All of these theories are equally plausible. But perhaps the most fascinating theory is the “Running Man Theory”
This theory is extremely logical. It starts with a unique quality to human beings. It is well known that some animals run faster than others. But a fact that seems to be forgotten is humans have an unparalled ability to run long distances. A cheetah can run approximately 70 mph or 30 m/s. They can accelerate from 0 to 20 m/s in 2 seconds, faster than a race car. However, this apparently great selective advantage has an equally great downside. This burst of speed causes the cheetah’s body to hear up to a point near brain damage. Furthermore, when they kill their prey they have to rest a significant time in order for the oxygen in their bodies to be replenished (5). This is a common theme amongst animals. In fact, only one animal has the capacity to run at a fast speed for a long period of time, human beings. This is the “Running Man Theory.” The ability of a human being to literally run their prey to death is the selective advantage that allowed our race to become so complex. It’s known as persistence hunting. By chasing our prey until it died, we were able to feed off large game without the use of tools. We were able to receive the necessary nutrients and proteins that lead to brain growth and complexity. Furthermore, this advantage led to the selective advantages of an efficient perspiration system, respiratory systems separated from muscles, an Achilles tendon, an arched foot, and upright posture (6). Each new trait expressed by the variation Shreeraj mentioned allowed those that had it the ability to chase down their prey better and access the nutrients from their game. This in turn allowed these traits to continue being passed down until all humans possessed them. Then, the access to food allowed our brains to grow and become more complex, resulting in tools, language, writing, culture, computers, and all the above. So not only is a selective advantage that we were able to run and persistence hunt like no other animals, but it had an effect like no other advantage on defining society and who we are today.
ReplyDelete1.http://email.eva.mpg.de/~paabo/pdf1/Khaitovich_Evolution_NatureReviewsGenetics_2006.pdf
2. http://www.dailymail.co.uk/sciencetech/article-1285270/New-evidence-humans-walked-upright-hot.html
3. http://www.howstuffworks.com/bipedalism.htm
4. http://www.onelife.com/evolve/manev.html
5. http://www.bluelion.org/cheetah.htm
6. http://www.trtreads.org/Chapter_2.html
-Robbie Thomashow
(diehardcubsfan93@comcast.net)