Monday, April 5, 2010

Convergent Evolution

On page 92, Coyne states that convergent evolution explains why different types of animals have simular forms in different places; "Convergent evolution demonstrates three parts of evolutionary theory working together: common ancestry, speciation, and natural selection" (94). Explain how these elements support why fundamentally different animals on different continents are so similar. Try to use specific examples. How does continental drift contribute to convergent evolution? How would evolution be different if we never had a separation of continents?


  1. Convergent evolution, as Coyne defines it, is "species that live in similar habitats will experience similar selection pressures from their environment, so they may evolve similar adaptations." (94) This is a huge piece of evidence behind those who support evolution. Coyne gives the example of how two different families of desert succulents, the cacti and the euphorbs, grow in separate continents, yet they "can look very much alike". They both include adaptations like "large fleshy stems to store water, spines to deter predators, and small or missing leaves to reduce water loss." (91) He continues by showing the similarities between the marsupials of Australia and the placentals of the Americas, for example: "the marsupial sugar glider, which glides from tree to tree just like a flying squirrel." (92)
    Now, how could this be? Similar species on different continents separated by oceans? Well, they had some help in the similarities department, because most of these species came from a common ancestor, which lived on a huge land mass called Pangaea which separated into the continents we have today, during continental drift. This process started about 200 million years ago, and it split many species onto separate continents as oceans formed between them. Without this separation of continents, we wouldn't see convergent evolution occurring on two opposite sides of the world, because the common ancestor species would never have been split into two different populations, in most cases.

  2. The three elements of evolutionary theory explain convergent evolution very well. Common ancestry works in that the two organisms being compared would share similar traits because they have a common ancestor, or a node in the tree of life. An example of how common ancestry fits into the concept of convergent evolution is the similarity of traits between marsupial mammals and placental mammals. Coyne said that common ancestry "accounts for why Australian marsupials share some features...while placental mammals share different features" (94). Speciation, defined by Coyne as "the evolution of different groups that can't interbreed" (6), fits into the mix well because it is the process by which each common ancestor gives rise to many different descendants. Finally, natural selection explains convergent evolution because it makes each species well-adapted and able to survive and reproduce in its particular environment. Continental drift contributed to convergent evolution because, as Brady said, the continents used to be one big land mass called Pangaea. When that land mass split, similar environments ended up being long distances away from each other and separated by oceans and other bodies of water, when before, they had been very close to one another. The similar environments mold the path for natural selection for the organisms - since the environments are similar, the specific traits needed to survive and reproduce in that environment are similar. Therefore, convergent evolution occurs partly because of the separation of continents. If we had never had a separation of continents, I believe that two such species would be even more similar. For example, if Pangaea had never split, the modern-day Australian marsupials and modern-day placental mammals would be living in much closer proximity to one another, where the environments are not only similar, they are almost exactly identical. If these organisms live in the exact same environment, they'd need to have some of the exact same traits necessary to survive and reproduce, so they would share many traits and be more genetically and physically similar to one another.

  3. Convergent evolution is the acquisition of a similar trait by two unrelated species. This happens for the most part because of very similar environments taht the two species live in. Common ancestry is involved because since the species already share some DNA, they are more likely to adapt in a similar way to a similar environmental challenge. Speciation is involved because speciation is when one species diverges because of two populations in different environments, while this is two species in a similar environment, so they become more similar instead of more separated. Lastly natural selection is involved becasue it is more likely to lead to similar traits for the two species if they live in a similar environments. This is because a similar trait would be an advantage for both species. Squids and mammals both have an advanced camera eye, with only one difference: the squid has blood and nerve vessels entering from the back of the retina and mammals have it from the front.
    If the continents never separated, we wouldn't find nearly as much diversity as we do now. The separation of species with different environments and no way of reaching the other continents make sure that evolution takes its different courses. But if they could move freely and werent as separated then evolution would not cause as great of differences in animals all across the planet. Separation of the continents and formation of islands provides room for much more diversity and difference in all species.