In the last chapter of the book, "The Meaning of It All," Shubin presents a simplified tree of life from unicellular organisms to humans. He notes several key features in the development of humans, including multicellularity, bilateral symmetry, skulls, hands and feet, a three-boned middle ear, and a bipedal gait with large brains (p. 183).
This list of features, of course, does not include all the important and defining characteristics of humans.
Select what you think are the most important traits humans have that were not covered by Shubin. These traits can be shared with human ancestors, or they can be entirely unique to human beings.
Then, explain how these features may have been selected for over evolutionary history, drawing connections to at least one theme of biology in addition to evolution.
- Vincent Fiorentini
(vincent@panatechcomputer.com)
First of all, Vince, I think Shubin did cover the general most evolutionary important features.
ReplyDeleteAs to what is 'most important', I am going to answer that question as to what makes us most uniquely human, and in my opinion that is the ability to reason complexly and the ability to perceive oneself. I suppose this would go under what Shubin would consider a 'large brain'.
I chose these because, to my knowledge, no other organism is able to do either of these things and are in part of what put humans at the top of the food chain.
Complex Reasoning: The fact that humans possess cognition, which is revealed in our ability to problem-solve, shows that we are already more evolved than other organisms who learn solely through means such as habituation, imprinting, or operant conditioning (Campbell 1125-1127). Seeing as how humans would not win in a fight against a bear or other large animal in nature, it was this ability to cognate that allowed humans to survive and overcome a Type II and III survivorship curve (Campbell 1178) by feeding smartly. This ability to reason eventually also pushed us to the top of any desirable food chain (interdependence in nature) by developing weapons and tools and domesticating other animals for our benefit.
Self-Perception: I believe that the ability to perceive oneself, and not encounter utter confusion as a dog would when facing a mirror, leads to some type of emotional homeostasis. Many studies have been done as to what and how some triggers may affect our emotional homeostasis such as the one involving ‘anxiety-related thought suppression’ exhibited in this journal article: http://www.neuropsa.org.uk/montreal-congress-july-2008-poster-abstracts. Additionally, I think self-perception is an evolutionary advantage because those with a stronger hold on their emotions are able to attract more fit mates, eventually improving the gene pool.
(Jackie Edelson, jedelson92@hotmail.com)
One characteristic we humans, Homo sapiens, share with our past ancestors is the opposable thumb. Simply put, the opposable thumb allows animals to grab things, which is something many animals cannot do! The ability to grab things led to the development of fine motor skills among humans, and other animals alike such as the Chimpanzee. This development of fine motor skills allowed these organisms to create tools, which played a very important role in the survival of ancient human ancestors. Millions of years ago, before an opposable thumb was a characteristic on all human species, there was variation within the ancient human population. This variation could have been caused by mutation, “a change in the nucleotide sequence of an organism’s DNA, ultimately creating genetic diversity” (Campbell 344) or transformation, “a change in genotype and phenotype due to the assimilation of external DNA by a cell” (Campbell 306). The variation included two types of human-hand characteristics: a hand with an opposable thumb and a hand without an opposable thumb. A certain environmental pressure, such as low amounts of prey, favored the variation of humans that had an opposable thumb. Eventually, natural selection, “a process in which organisms with certain inherited characteristics are more likely to survive and reproduce than are organisms with other characteristics” would take its course (Campbell 456). The humans with opposable thumbs would be able to construct primitive tools, like spears and clubs, to help capture prey and find food. They can be considered to be the species with the “selective advantage”. The variation without opposable thumbs would be at a huge disadvantage. Hunting down prey with no weapons or tools would have been a very arduous task, and the no-thumb variation would eventually be bred out of the population. When the entire population has some form of the selective advantage, in this case the opposable thumb, the process of adaption is complete. All in all, the ancient human ancestor whose population contained both opposable and non-opposable thumbs has evolved into an entire new species of humans. In order for the species with the opposable thumbs to be considered completely evolved, one very important criterion has to be met. The new species of humans would have to be different enough from the non-opposable thumb species that the two would not be able to reproduce with each other. The thumb-possessing species would be completely evolved once this happens.
ReplyDeleteMikey Ling (mikeyling@ymail.com)