How did humans develop such traits that are similar to predecessors but still different? More importantly, how do humans and such wildly different organisms as fish and reptiles all have similar adaptations even after long periods of diverging evolution? Explain how continuity and change affected evolutionary patterns in such a way that humans could have similar genetic features as other, completely different animals, and give examples of more connections among very different animals.
Eugene Bulkin
Evolution says that we developed from a common ancestor. Our common ancestor with other mammals lived later than our common ancestor with fish. One of Shubin's major points is that our similarities with various animals exists because we are not really new organisms, but rather "products of a convoluted history" (186). Take, for example, our eyes. They are very complex structures that allow us to see the world in color, they have protective adaptations, and work with our ear to keep us coordinated. But at their basic functions, they are specialized parts of our body that allow us to use light to experience the world. This basic function is shared with many animals, in the form of compound eyes (flies) and patches of photoreceptors (polychaetes). These very different structures, are all used by very different animals to perform different adaptations of the same function.
ReplyDeleteAs Jeremy said, “evolution says that we are from a common ancestor” (Jeremy). He further quoted Shubin that we are “products of a convoluted history” (186). Through evolution there is variation between genes because mutations and sexual reproduction recombination; however, evolution does not call for a complete new set of genes. Many of our genes are similar to the genes of our common ancestors, but it is the slight variations in our genes that make us different from other animals and organisms. We can examine the divergence from this common ancestor with phylogeny trees (both morphologically- and molecularly-based).
ReplyDeleteFrom the common ancestor of all animals diverged sponges and animals with true tissues. Although sponges have no true tissues, no bilateral symmetry, and no spine, sponges may be more similar to humans that you think. According to Professor Degnan, “nearly 95 percent of all genes associated with human disease can be found [in] sponges” (qtd. in http://www.sciencealert.com.au/news/20092907-19478.html). In addition, intensive studies on sponges have been conducted to learn more about embryonic stem cells, the similarities between human and sponge stem cells, and how to apply this information to use human stem cells to generate the cell types scientists want to create (http://www.sciencealert.com.au/news/20092907-19478.html).
More closely related invertebrates are the Eumetazoa, which consist of classes such as Cnidaria and Echinodermata. Shubin discusses the similarities between humans and sea anemones in a later chapter. But how could something that “eats and poops” through the same opening be similar to us? Both humans and sea anemones have Hox genes that are critical to the development of body plans. On page 114, the diagram Shubin provides illustrates that the Hox genes within both humans and sea anemones are involved in the development of the front end and back end of both organisms. In addition, the human Hox genes are involved in the development of the human central region. “Versions of the Hox genes appear in every animal with a body,” (110) says Shubin, but through evolution, there have been mutations and changes in the sequences of Hox genes and the number of Hox genes in an organism, creating differences among animals. Nevertheless, the Hox genes are involved in the development of body plans in both humans and sea anemones, giving us (humans) a similarity among a seemingly completely different animal.
Another animal that may seem completely different from humans are sea stars. An invertebrate that uses a water vascular system to move at an incredibly slow rate (yes, those fast moving echinoderms in the video we saw in class were actually in fast-motion!) with no brain (instead a central nerve ring and radial nerves) and five arms is similar to humans. Both humans and sea stars develop via deuterostome development (anus to mouth). Both have radial, indeterminate cleavage at the eight-cell stage; both develop their coeloms from mesodermal outpocketings of the archenteron; and both develop their anus before their mouth as the anus develops from the blastopore.
So even with millions of years of evolution at work, there are still many commonalities between our genes and the genes of animals that seem completely different from us. However, looking at a phylogeny tree, we can see we are more closely related to frogs than earthworms. Nonetheless, all organisms come from a common ancestor, and because of that, we all share something in common.
(Bobby Muttilainen, rmuttilainen@gmail.com)