Wednesday, March 10, 2010
The evolution of land mammals to aqautic mammals
In Chapter 2, Coyne explains that evolutionists believe that whales, aquatic mammals, descended from terrestrial animals. Many creationists believe that whales couldn't have descended from terrestrial animals because animals evolved from aquatic animals to terrestrial animals. Having animals evolve from terrestrial animals to aquatic animals doesn't follow the idea of natural selection and adaptions used to back up the idea for evolution. What evidence do scientists and evolutionists have that whales could have descended from terrestrial animals as explained in the book? How is evolving from terrestrial animals to aquatic animals a selective advantage in some cases like in the case for the whale? What other examples of animals have evolved into something they once had and how is that an example of natural selection. What environmental conditions could have changed to cause the animals to change genetic information? Use outside sources for the last question including your Campbell book.
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There is no doubt that whales descended from terrestrial animals. On pg.50, Figure 12 shows the evolution of modern whales through the fossil records. The shift in bone arrangement clearly delineated by the fossils leaves no doubt that whales evolved from a terrestrial cousin of Indohyu. In addition, the presence of vestigial traits such as reduced pelvis and hind legs, proves that the whale shares a close common ancestor with land animals that have pelvises and hind legs (48). DNA sequencing has also confirmed this.
ReplyDeleteIt may seem backward for the terrestrial animals that are the whales’ ancestors to return the water after these land animals actually originated from aquatic animals in the first place. The terrestrial whale ancestors were not evolving backward at all; in fact quite the opposite. After living on land for millions of years the terrestrial ancestors of whales had acquired several traits that no aquatic animals at the time had. The terrestrial animals had hair, mammary glands to feed their young milk and are endothermic (warmed by heat generated by metabolism). When these animals colonized the water again, they did not evolve backward; these mammal traits did not disappear. Instead, these unique mammal traits only before present on land evolved to better suit an aquatic environment; thus promoting forward evolution.
The terrestrial ancestors of the whale which spent more and more time in the water began to branch off from the other terrestrial mammals. Living the water could be a selective advantage because there is more prey to eat in the water that a non-swimming counterpart couldn’t capture. With more food, the mammals living in the water had more energy to survive and reproduce, and thus a selective advantage.
There are several reasons that the proto-whales could have been driven to colonize the water in the first place. The Coyne’s book suggests that the early whale ancestors evolved to inhabit the water when they did because once the dinosaurs were extinct, an open niche of preying on seafood was open (51-52). Another possibility is that another land species could have invaded the area where the land ancestors of whales lived. In result, the whales may have been forced to live closer and closer to the sea, until eventually the proto-whales most suited for the aquatic environment survived.
Samantha explains very well the evidence gathered by scientists and evolutionists on how whales descended from terrestrial animals. To answer Anika's other question, on how evolving from terrestrial mammals to aquatic mammals could be a selective advantage, Samantha also addresses this, noting how there might be an unoccupied niche that the whales might have migrated into. The whales may have been similar to other semi-aquatic mammals, such as otters, beavers, seals, walruses, or muskrats. An example of some of the early ancestors of whales would be the Ambulocetida, which scientists believe descended from dog-like ancestors. Ambulocetus was similar to otters in terms of body shape and method of swimming (and also to modern day whales, in that respect). The Ambulocetus could very well have competed with other animals that were more adept predators on land with stronger, more well-suited legs, and eventually the individual Ambulocetuses (Ambuloceti?) that were able to stay in the water for longer and longer periods of time and able to swim faster and farther were the ones who survived and reproduced. After a long time, certain characteristics of earlier life resurfaced, while other characteristics, such as the method of swimming, the need to come up for air, and the bones in the fins, were retained. Certain characteristics were also developed, such as the ability to swallow underwater, and the increased efficiency of the lungs and circulatory system. The evolved whale would fill a niche previously not filled, or be more successful in an already occupied niche. Similar animals to the whale that have evolved to return to the water include the seal. Though the seal has not completely gone back to an aquatic life, the seal is obviously more suited for life in the water than on land.
ReplyDelete(Sources: http://www.bbc.co.uk/nature/wildfacts/factfiles/432.shtml and http://www.neoucom.edu/DEPTS/ANAT/Thewissen/whale_origins/whales/Ambulocet.html)