Homologies and Analogies

Homologous Trait: The Forelimb

The forelimbs of a lizard and a rabbit are examples of a homologous trait. A lizard is a reptile whereas a rabbit is a mammal, but they both share a common ancestor that also had forelimbs. A rabbit and a lizard both have forelimbs. Their forelimbs all have the same bones, the humerus, the radius, and the ulna although they are both structured differently. A rabbit’s forelimbs are located underneath its body, while lizards forelimbs are located on the sides of its body.  A lizard mainly uses its forelimbs to run, climb, or cling to rocks. The rabbit’s main locomotion is hopping. Fossils of a prehistoric tetrapod called Eusthenopteron were discovered and had distinct humerus, radius, and ulna bones.

Analogous Trait: Wings

Moth wings and bird wings are an example of an analogous trait. The Moth and Bird have not evolved from a common ancestor that could fly. Instead they both developed wing structures due to selective pressures in their environments. The wings are used as a form of locomotion.

Protein Synthesis

AGTCATACACCTGGGAACTCACGGTCACCTTGTAATAGATCTCAA

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Malthus' Influence on Darwin's Theory of Natural Selection

Although many people influenced Charles Darwin’s Theory of Natural Selection, I believe Thomas Malthus’ famous work An Essay on the Principle of Population (1798) was the most influential. Malthus stated in his book that a growth of a population would always be higher than the amount of food and resources available to that given population.  He argued that if population sizes were not controlled, famine and misery would plague the world. 

Darwin grew upon Malthus’s idea about population growth. If more offspring were produced than available food and resources, then that would make for some competition between individuals. The more offspring produced also meant more variables in traits. Some individuals would have a better chance of surviving.

http://www.ucmp.berkeley.edu/history/malthus.html

           

Malthus’ work helped Darwin explain how all organisms can potentially reproduce as much as they want, but with not enough resources to support all the population growth, only the strongest will survive.

           

Due to the amount of people that had other influences on Darwin’s work, I believe he would have come to the same conclusions about natural selection. His grandfather Erasmus Darwin introduced a similar idea about competition for resources in writings that Darwin read.

           

The attitude of the church had a huge influence on Darwin.  During that time in Britain, there was major political reform occurring and other proponents of evolution were well known atheists and socialists. He didn’t want to upset his wife and her strong religious beliefs. It wasn’t until Alfred Russell Wallace published an article similar to Darwin’s theory that Darwin quickly finished his research. He didn’t want Wallace receiving the credit for the theory of natural selection since Darwin was the original developer of it. He received a great amount of scholarly support and eventually the scientific community adopted his theory on evolution.