Jeremy Solomon
imabum14@gmail.com
Sunday, April 3, 2011
Evolution of Behavior
We talk mostly about the similarities between the physical structures that make up different organisms. Scientists try to use the fossils they find to reconstruct some behaviors of their discovered organisms, but the evolution of behavior is difficult to track, because of the lack of evidence. Discuss the methods with which scientists discern behavior from bones, and some evolutionary trends that have been discovered among land animal history.
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The ability to be able to tell a good amount of an organism's lifestyle from its bones stems of the theme of structure relating to function. If one of the animal's bones is really large, then this part of it's body must be used often and have large muscles. All of this can be told from one bone because of common knowledge that if a bone is carrying a lot of wait and has a lot of force put on it, then it is important for it to be strong. Another tool is comparison of the bone to bones of animals today. For example, humans walk on their feet, therefore requiring them to have big quadriceps and large femurs. Instead of looking at bones individualy, scientists also look at them as a whole. These clues are often portals to the evolution of a species over time due to the stress put on it by the environment.
ReplyDeleteNot only was the transition of animals from water to land apparent in the pressence of gills but also through bones. One of the biggest discoveries was the capabilities of Tiktaalik's arm to do push-ups. This one bone explains how ancient fin's of waterbound animals became arms, and, "The size and extent of these muscles means that the humerus played a significant role in the support and movement of the animal" (http://chronicle.uchicago.edu/040415/armbone.shtml). This bone allowed them to predict the amount of muscle and even to figure out that this creature was, "built to navigate the bottom and shallows of streams or ponds, and even to flop around on the mudflats along the banks" (Shubin 40).
Jackie James
(jackie.james@comcast.net)
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ReplyDeleteLike Jackie said, scientists don't look at animals bones individually. Instead they look at how the structure of the bones reflects a body part's function. An example Jackie left out is the examination of hand fossils. The complexity of ancient human hand-bone structure show "potential for tool using... we can infer their existence. Though stone tools are not recognizable in an archaeological context until 2 to 2.5 million years ago, the level of workmanship suggests a long period of prior tool making... chimpanzees in the wild and in captivity make tools. Early hominids would have been at least this innovative" (Zihlman, Human Evolution Coloring Book). This is a variation of the method Jackie explained, comparing fossils to modern-day bones. Yet, there is a little bit of a twist. The scientists compared modern-day chimpanzees to early hominids, but they didn’t compare the bone structures of the two. Instead, they compared predetermined knowledge of the two. Scientists are able to make very credible predictions about the intelligence levels of early hominids with regard to chimpanzees because “chimpanzees are our closest relatives” (Lovgren, National Geographic News).
ReplyDeleteEven before the transition of animals from water to land, animals went through an evolutionary trend that still continues today: cephalization. Cephalization is “an evolutionary trend toward the concentration of sensory equipment at the anterior end of the body” (Campbell G-7). Jackie says Tiktaalik’s ability to do push-ups was one of the biggest discoveries in terms of evolution. The formation of a shoulder, elbow, and wrist joint was a very large step in the transition from water to land, but even before this happened amphibious animals underwent cephalization. Tiktaalik’s bone structure indicates a bilaterally symmetric body plan, and “bilateral symmetry implies a directionality to the animal… With movement in a specific direction comes development of sensory equipment at the end that encounters the environment first” (coa.edu). Cephalization is a very obvious evolutionary trend that continues as animals become more complex. The transition from water to land called for more complex animals, and Tiktaalik was the manifestation of this transition. Tiktaalik displayed bilateralism, and essentially cephalization, which was a crucial evolutionary step during the transition.
Mikey Ling (mikeyling@ymail.com)
Jackie mentioned the enlargement of organs that correspond directly to the slow cephalization of species. Mikey mentioned cephalization as a part of Tiktaalik and the transition from water to land. The gradient of complexity that generally stems from water organisms to land organisms is visible in the Campbell textbook in chapter 33 when the basic central nervous structure of cnidarians debuts the importance of a central nervous system in mobility. Phyla Porifera does not require a central nervous system to filter feed since Porfira filter feed passively. Although land animals are more complex in their cephalization, marine and fresh water organisms (especially those that engage in hunting for food such as organisms seen in Phylum Mollusca)present a complex nervous system because evolution benefited organisms that can maintain enough mobility to give chase to a food source that consequently also achieved greater mobility. Because evolution has directly benefited organisms that have the ability to hunt down their prey, cephalization has directly benefited these organisms. Greater intelligence also corresponds to a better rate of survival. This attests to Neil Shubin's comparison of the shark and the human where "virtually all are nerves are present in sharks". (92) The difference between a shark and a human though, is the degree of cephalization that occurred in evolutionary history. A shark does not require as large a central nervous system with complex systems resting in the brain (although it does have a brain suited for the marine environment and marine obstacles). On the other hand, a human being experiences a variety of obstacles on land which a shark does not experience in the marine environment such as the benefit of using hands for fine motor movements or learning language to live in groups (which sharks do not require the complex nervous system for). A greater intelligence is clearly an asset and therefore cephalization is progressing in what is known as the Flynn Effect which was found in standardized IQ testing where the average IQ score needs to be adjusted because "IQ performance has been rising steadily all over the industrialized world since the 1930s." (Flynn, 1987, 1994, 1998, 1999) This trend is evidence that natural selection benefits individuals with a higher intelligence because it increases their ability to survive in sociocultural systems.
ReplyDeleteYekaterina Khavkhalyuk (kittykatx93x@yahoo.com)