Evolution's History

Before Darwin

Life was first understood through the lens of religion. First, we will explore the Christian perspective on how life forms came to be.

Archbishop William Paley wrote a book called Natural Theology, making the point that life is so complex that it implies that there is something/someone who designed it, and that someone must be god.

In order to account for fossils of organisms that do not exist anymore, French anatomist came up with the theory of catastrophism — meaning that some animals died in catastrophes and went extinct.

Another French anatomist, named Jean-Baptiste Lamarck, came up with the idea of inheritance of acquired characteristic, meaning that certain body parts can develop when they are used a lot. However, this is written off as a teleological explanation, which is an explanation that explains the existence of something by citing a goal of purpose of that thing.

In summary, before Darwin, biologists thought that we lived in a static world, order is inherent (teology), and variation is just "noise."

Darwin's Voyage on the Beagle

In university, Darwin learned the ideas that are discussed in the previous section. Darwin was invited on a voyage to be the "educated gentlemanly companion" to the captain. For five years, he sailed around the world, killing animals to collect them.

One of the books Darwin took with him was the Principles of Geology, which introduced the idea of uniformitarianism, the idea that the present is a result of a lot of small changes over time. Many thousands of years of small change.

Lyell's theory implied that, contrary to christian belief, the earth was older than 4000 years old.

In South America, Darwin was exposed to the diverse fossil record there, as well as the genetic and geographical variation that there was in the plants and animals.

The Galapagos Islands

At the islands, Darwin encountered the Galapagos Finches. They clustered into four main types of beaks, which are categorized by the types of beaks. This was an example of adaptive radiation.

Darwin's Key Observations

• Organisms tend to produce more offspring than is needed to keep the population stays stable, but yet, the population stays stable, meaning that a lot of organisms die.

  • One work that had a large influence on Darwin was Malthus's Essay on the Principle of Population, which implies that because population increases exponentially and resources increase linearly, there is a point of crisis where those two lines meet.

• Variation is innate to life, they vary. Also, offspring tend to look like their parents, meaning that variation is passed on.

• Death is not evenly distributed. Darwin thought that, perhaps, the organisms with better suited beaks were more likely to survive because they have the ability to eat more. The variation that gave them an advantage makes them more likely to survive. This is his is survival of the fittest.

• The environment is the agent of variation. It favors one range of variation over others, and therefore, it is more likely to survive.

Change over time is caused by differential reproductive success (fitness).

Reproductive success is not how many times you have sex, but how many children you have that also eventually have children.

Alfred Russell Wallace

Wallace came to the same connections during his trip to the archipelagos in Malaysia. Both wrote papers which were presented to the Linnean society.

Darwin's Main Contributions

• Collected eveidence to document the occurance of evolution

• Provided a natural mechanism for evolution

• Estabstalished a methodology for inferring about the processes we can't see from the preserved results.