Evidence of Evolution
09/12/2010 § Leave a comment
“Evidence of Evolution” was our second to last lecture for the Evolution unit. We’ve learned that to survive the different eras, or ‘stages’ of evolution, all an animal really needs to do is survive and reproduce. Surviving takes into account food, shelter and competition and reproduction is basically continuing the species.
In class, we learned that scientists use fossils to study the preserved imprints and mineralized remains of animals and organisms that lived millions of years ago. Fossils are usually buried under rocks, deep under the strata and aren’t seen until the earth pushes them up and exposes them to scientists. Fossils can also be made into rocks that preserve organic forms perfectly. This happens through trees and the amber excreted by trees. An example of this is seen in the movie Jurassic Park (the first one) where John Hammond has a walking cane with the fossil of a mosquito as means to hold the cane. The mosquito fossil is the result of a tree excreting the gooey substance amber onto the mosquito. The substance traps the mosquito and preserves the entire organic form. This is a wonderful way to make a fossil because unlike rocks underground, the organic form is completely preserved and does not mineralize nor will it decay or decompose. This way, scientists can study the actual organisms.
Fossils, with the help of radioactive decay and radiometric dating, can help determine the age of the fossils, therefore an approximation of how long it had been since the organism existed. A more recent example of this is whale evolution. Fossils found in the Sahara Desert (?) recorded that apparently, 50 million or so years ago, at 3 meters long, whales used to resemble what we call today sea lions. They even have the limbs and are almost completely aquatic.
Fossils were also used to study the evolution of horses. Thanks to the wonderfully mineralized specimens, scientists could figure out that millions of years ago, horses were about the size of an average dog. The scientists were also able to figure out that horses used to run on four toes, then three, then eventually the one large toe that we call a hoof. The fossils also showed that a horse’s teeth grew throughout the years, most likely to make chewing and grinding grass easier.
In class, we heard the word homologous again. Just when we thought we left that word behind after the Reproduction unit and the entire “Why sex?” essay question, to this day, the word homologous haunts us.
Well, no, not really.
But a homologous characteristic between organisms shows anatomical similarities. These include similarities such as limb structure, being a vertebrate, and normally skeletal structure. Animals that are homologous because of their skeletal structure are humans, sea lions, wolves, opossums, moles, bats, whales and even elephants. Who knew? Homologues are so important because they suggest one common ancestor. We must understand that animals or organisms are not related but share a common ancestor. They’re two very different things.
Fossils also introduced Lucy. According to the specimens a few scientists found, she walked like a human, even if she had the skull of a primate. Therefore, I consider her half monkey, half human. However, her presence and existence millions of years ago is hardcore proof that maybe, just maybe, monkeys and humans share a common ancestor.
Finally, the last evidence of evolutions lies in the biological molecules in organisms. The differences and similarities of proteins (more specifically, amino acids) in two organisms show how long it’s been since they shared a common ancestor. With this information, scientists can keep track of when the two organisms had a common ancestor. Also, DNA also provides information as to the relationship between two species. Thanks to the nitrogen bases, scientists can determine the similarities and differences between organisms’ genetic information.
Obviously I don’t wholly understand the concept of molecular phylogenetic trees yet so I’ll be going to the classroom and asking about them tomorrow morning before homeroom.