These types of evidence include: fossil records, embryonic development, DNA comparison, and behavioral similarities.
Although Shubin provides specific evidence for the role of each of these types of support as they relate to Tiktaalik, no one alone can be completely reliable to draw a full conclusion. Some, however, are more revealing than others.
Of the types of evidence Shubin provides for the connections between humans and previous animal species, which do you think are the most reliable? Which do you think are the least reliable? Explain, using outside information to validate your claim.
-Vincent Fiorentini
vincent@panatechcomputer.com
I think behavioral similarities are probably the least reliable source of evidence for connections between humans and other species because most behavior—which is strictly an animal characteristic in the first place—only relates to the most effective way to survive and reproduce, whatever that may be, which is usual a product of a species environment. However, if by “behavior” one was actually referring to the way an organism/species learns, then it becomes a more reliable source. This is because how a species learns is probably related to brain function/capacity, which since humans are at the top of the food chain and have the highest thought capacity, is an evolutionary advantage. For example, an organism with the ability for cognition is more evolutionarily advanced than an organism that can only learn through associative learning, which is more evolutionarily advanced than an organism whose main source of learning is from imprinting. (Campbell 1126-1128). Though this can not be the only way to relate humans back to their predecessors because not all animals’ behavior/learning style can be observed. Also, there are no sub-categories within each learning style, so a dog would seem as closely related to humans as a chimp because both learn by associative learning.
ReplyDeleteA better, more reliable, type of evidence as to human relatedness to animals is studying embryonic development. This is because one can examine an organism’s structure in its development and later how those structures function in the full-grown organism. For example, as Shubin points out on pg. 30-31, humans are much more closely related to birds than, let’s say, snails because both humans and birds develop limbs from the mesoderm in the pattern discovered by Sir Richard Owen. This type of evidence also relates to using fossils as a way to fill-in-the-blanks about our past. Fossils, too, use the idea of comparing structure (and perceived function) of ancestor organisms to modern ones. In this way, scientists use fossils as a way to make a timeline of our evolutionary history based on what bones/shapes/structures occurred first and at what point in time they did so. Since fossils are basically the only tool we have that can provide information about ancient organisms, it is the best tool we have for that purpose.
Finally, the best type of evidence is most certainly DNA comparison, when possible. (I understand that it is unfeasible to expense of extracting DNA from fossils for wide laboratory use.) Though the logic of ‘bigger is better’ doesn’t apply for number of chromosomes in an evolutionary sense, seeing as how “Ophioglossum reticulatum, a species of fern, has the largest number of chromosomes (thread-like bodies in a cell's nucleus that hold the genes) with more than1,260(630 pairs)” (Trefil, James, 1OO1Things Everyone Should Know About Science, p. 106.), the logic that the genomes most similar to humans seems to be the most evolutionarily advantageous does apply. Chimpanzees “are 96 percent similar to” humans’ sequenced genome and thus “our closest living relatives” http://news.nationalgeographic.com/news/2005/08/0831-050831_chimp_genes.html. I accept this information because I hold DNA testing to a high respect of reliability, however scientists John Grehan and Jeffrey Schwartz do not believe genetic testing is always done in the most accurate method and thus chose to consult more structural evidence, such as “humans share at least 28 unique physical characteristics with orangutans but only 2 with chimps and 7 with gorillas”, when they dubbed the orangutans our closest living relative (http://news.nationalgeographic.com/news/2009/06/090623-humans-chimps-related.html). I also disagree with the pair because I think their claimed ‘unique physical characteristics’ could be arbitrary and up for debate.
I agree with the statement that Jackie made about how behavior is the least effective method of relating humans to other organisms in the pathway of evolutionary history. As stated by the Campbell textbook, "an animal's behavior is the sum of its responses to external and internal stimuli"(Campbell 1120). As different stimuli are exposed to an animal over its life span, it develops a pattern of reacting, which is what we know as behavior. Since behavior is a product of external environment for the most part, it cannot be viewed as a reliable reason for determining the relatedness of a particular species of animal to humans. In addition, I partially disagree with Jackie's statement that behavior is a euphemism for learning, because that is untrue. Just because different animals learn in similar ways, does not necessarily link them closer together than with other species. As stated in Campbell, animals may perform a certain behavior because it may be advantageous in natural selection, and if it is, then other species of animals would repeat this behavior to gain the same advantages. Thus, just because animals would use the same advantageous strategies to survive and reproduce, doesn't necessarily mean that the species would be related. Since learning is not interchangeable with behavior, determining interspecies relatedness by behavioral patterns is not the most accurate method.
ReplyDeleteI think that fossils are slightly more effective in helping clarify the connection between different animals, because they provide scientists with an actual outline of a body, which can show changes throughout evolutionary history that can be seen with the naked eye. As described throughout Your Inner Fish, fossil records are helpful because they can preserve such long periods of time, and show physical likeness between animals that were evolved differently or later on. However, fossils can leave voids in their evidence, as "large parts of the body-soft tissues, for example-simply do not fossilize readily"(Shubin 139). As Shubin stated, the fossils, because they have endured time, often cannot provide us with certain links, because of decay.
Embryonic development is a much more accurate way of determining species relatedness, because of the fact that if we can determine how different animals grow and form tissues, we can understand how closely related humans are to other animals. This is due to the idea that the way that organisms develop and what cells and tissues develop from certain parts of the embryo can show where evolution might have diverged, and which species develop similarly, which can determine how closely related they are. For example, as seen in Campbell textbook pages 1022-1035, the way that frog, sea urchin, mammal, and chick embryos cleave and gastrulate can show scientists the relatedness of these animals. By examining which organs and body tissues develop from certain parts of the embryo, scientists are able to see the similarities between different animals during the embryonic development stage. These similarities can support connections between animals that seem related, because they can show where different patterns of development branched off in evolutionary history, and how closely humans and other animals are related, based on body composition, and what body parts correspond to parts of the embryo. Although this method is more accurate and detailed, it still does not allow for deeper understanding or connection.
I again agree with Jackie that DNA comparison is the best way of identifying the closeness or likeness of different species of animals in evolutionary history. Scientists often study the DNA of chimpanzees and humans to gauge how closely we are related, and how far down in history our species diverged from a common ancestor. By examining human and chimpanzee DNA, scientists were able to note very close similarities, but also slight differences that could explain why certain conditions or biological cases occur in only humans or only chimpanzees, not the other. By studying the DNA code, scientists discovered that our DNA is about 95% related to chimpanzee DNA, and that only slight differences between the two genomes can be noted. For example, according to the Journal of Creation, "While 18 pairs of chromosomes are ‘virtually identical’, chromosomes 4, 9 and 12 show evidence of being ‘remodeled.’ In other words, the genes and markers on these chromosomes are not in the same order in the human and chimpanzee". Scientists also found that the Y chromosome in both species were very similar, but were different in size and number of markers on the genes. Thus, by examining DNA code in both humans and animals believed to be closely related, we are able to understand how we are connected and why we are more associated with primates than other types of animals. Thus, because of the number of nucleotides and specificity of the human and chimpanzee genomes, it is easier for scientists to pinpoint differences and similarities, which is why DNA comparison is the most effective and accurate way of linking together organisms in evolutionary history.I again agree with Jackie that DNA comparison is the best way of identifying the closeness or likeness of different species of animals in evolutionary history. Scientists often study the DNA of chimpanzees and humans to gauge how closely we are related, and how far down in history our species diverged from a common ancestor. By examining human and chimpanzee DNA, scientists were able to note very close similarities, but also slight differences that could explain why certain conditions or biological cases occur in only humans or only chimpanzees, not the other. By studying the DNA code, scientists discovered that our DNA is about 95% related to chimpanzee DNA, and that only slight differences between the two genomes can be noted. For example, according to the Journal of Creation, "While 18 pairs of chromosomes are ‘virtually identical’, chromosomes 4, 9 and 12 show evidence of being ‘remodeled.’ In other words, the genes and markers on these chromosomes are not in the same order in the human and chimpanzee". Scientists also found that the Y chromosome in both species were very similar, but were different in size and number of markers on the genes. Thus, by examining DNA code in both humans and animals believed to be closely related, we are able to understand how we are connected and why we are more associated with primates than other types of animals. Thus, because of the number of nucleotides and specificity of the human and chimpanzee genomes, it is easier for scientists to pinpoint differences and similarities, which is why DNA comparison is the most effective and accurate way of linking together organisms in evolutionary history.
ReplyDeleteSources:
Campbell textbook
Your Inner Fish
http://www.answersingenesis.org/tj/v17/i1/DNA.asp
Matt Kim
(matthewkim0803@gmail.com)