Tuesday, March 23, 2010

Fossils, key to evidence of evolution

Coyne stated that "transitional species is not equivalent to an ancestral species; it is simply a species showing a mixture of traits from organisms that lived both before and after it." (35). Then simply, what does the transitional specie serve as? Also, why is it such a controversy when a transitional specie is found containing a features of two different species? Also what are the possible forces that drove an organism of the same specie to adapt one specific feature while giving up another feature?


  1. A transitional fossil is any fossil which gives us information about a transition from one species to another. A transition simply means that, down through time, there was some sort of change. Charles Darwin stated in his book "On The Origin of Species" that "we should always look for forms intermediate between each species and a common but unknown progenitor; and the progenitor will generally have differed in some respects from all of its modified descendants." Transitional species then serve as the evolutionary "links" between two populations of organisms. One of the greatest examples of a transitional species is the Tiktaalik rosae, which provides the evolutionary link between fish and amphibians and tells us the story about how aquatic vertebrates came to live on land. Another example is the Archaeopteryx, which is said to provide the evolutionary link between birds and reptiles, but whose finding has been extremely controversial. According to Tim Beardsley's article "Fossil Bird Shakes Evolutionary Hypotheses," fossils of older birds have been found in older rock strata than Archaeopteryx, which creationists use to suggest that either Archaeopteryx is not a transitional species or that rock dating is inaccurate. Creationists also say that in order to prove that Archaeopteryx was a transitional species, scientists have to explain why feathers develop from a different part of the bird’s embryo than scales do from a reptile’s embryo. Therefore, a person who supports the theory of evolution would have to show how one could have replaced the other in an evolutionary manner—without violating the rules of biology. One of the main forces that drives an organism of the same species to adapt one specific feature while giving up another feature is the environment. For example, land mammals migrated to the water and became modern-day whales and marine/aquatic animals due to predation and the abundance of food in the water. Their gradual movement acted as a selective advantage for them because it helped them survive and reproduce. In this case then, the transitional species would be the species that had just began moving into the water from land, and it would provide the evolutionary link between the land animals that came before it and the marine/aquatic animals that came after it.


  2. Transitional species, commonly called missing links, serve an imperative role in proving the Evolutionary Theory. They are the fossilized remains of certain organisms that are crucial in linking together two different species. Like Sara mentioned, they show the transition through which an organism developed from one kind to another. They function more or less as a middle point because “they span the gap between two very different kinds of living organisms” (Coyne 32). There are many known species that are considered to be transitional, such as the Tiktaalik rosea-the missing link between fish and amphibians, the Saahelanthropus tchadensis-a link between chimps and humans, the Archaepteryx-a link between birds and reptiles, and many many more.
    The concept of transitional species, however, can be very controversial. It is commonly stated by critics of evolution that there isn’t even such a thing like a transitional fossil. This is because although they explain the evolutionary transition of one life-form to another, they only exemplify snapshots of this process. Due to the fact that only a very small percentage of all life-forms that have ever existed can be expected to be discovered, there are several gaps in between the transitional fossils and the two species they connect. Therefore critics think that transitional fossils are simply a “convenient way to explain off the lack of snapshot fossils that show crucial steps between species” (Wikipedia). Also, an additional reason for this controversy is because many critics “simply don’t want to see the truth.” They will never be satisfied with the fossils because it’s not going to be possible to show a very close and exact transitional chance because “the discovery of one missing link only creates two more so-called missing links on either side of the discovery”. (Dawkins) In addition, Alan Haywood explains that “Darwinists rarely mention the whale because it presents them with one of their most insoluble problems. They believe that somehow a whale must have evolved from an ordinary land-dwelling animal, which took to the sea and lost its legs ... A land mammal that was in the process of becoming a whale would fall between two stools—it would not be fitted for life on land or at sea, and would have no hope for survival” (Creation and Evolution). Regardless, the evolution of whales has been linked with the transitional fossil, Ambulocetus, described as a three-meter long mammalian crocodile. It seems as if though regardless of what scientists find, one side, either the critics or the supporters, will oppose the other side’s opinions. (continued on next post)

  3. (continued) There are many possible forces that drove an organism of the same species to adapt one specific feature while giving up another. One of the biggest influences, like Sara mentioned, is the environment. For instance, the Tiktaalik Rosea was driven out of the water and onto land. Its specific features, such as its unfish-like neck and limbs that were “part fin, part leg” (Coyne 38), were giving it a selective advantage in a terrestrial environment, as opposed to its aquatic one, and hence they decided to venture onto land and become the first land-dwelling organisms! Their gradual movement acted as a selective advantage because it may have allowed them to hunt food more easily and to escape from predators that could be lurking in the waters. Eventually over time, they gave up their traits that made them suitable for water, such as gills and fins, and exchanged those for ones that would help them survive on land, such as sturdier bones and more efficient lungs. The environment can passively select traits that are fit based on a myriad of variables, such as temperature, elevation, availability of resources, etc (Actionbioscience.org) The reason some features of an organism are lost while others are introduced is because it allows them to be better adapted to their habitats and survive and reproduce more efficiently.