Structure

Darwin once called The Origin of Species 'one long argument', but it can be broken down into two or more manageable parts. One part considers whether modern life forms have arisen by evolution or separate creation. The second part of the The Origin of Species considers the process that causes evolution. Darwin argues that the process he calls natural selection drives evolution.

Evolution or Separate Creation?

According to the theory of evolution, the various forms of life on Earth - trees and flowers, worms and whales - all descend from common ancestors. These ancestors looked very different from their modern descendants.?

According to the theory of separate creation, the ancestors of the modern forms of life looked much like the modern forms, and the various forms of modern life have separate, rather than common, origins.

The Theory of Evolution by Natural Selection?

Darwin argues that the process he calls natural selection drives evolution.

What is natural selection?

Chapter 1&2 Two important concepts are?heredity(also called inheritance)?and variation. Darwin began his book with heredity and variation because his whole theory depended on them.Modern view: genes and DNA to describe heredity(inheritance).

Chapter 3&4 He begins by connecting his earlier material on heredity and variation to the theory he is about to discuss and then gives an advance overview of the theory of natural selection itself:?

Two questions that Darwin were faced with: what is the explanation for adaptation, and what is the explanation for continual evolutionary change.

First Question:

adaptation:?differs slightly from its colloquial usage. In colloquial use, adaptation ususally refers to change over time. We might talk about someone 'adapting' to a new job - that is. how they adjust their behaviour to the new conditions.?When Darwin talks about 'all those exquisite adaptations' he is referring to structures such as hands and eyes, that exist in a form that is well designed, given the life that the creature is leading. Eyes, for instance, have an optical structure, with a lens and light-sensitive cells, that enables them to be used for vision. An eye is an example of an adaptation. An adaptation is any part of a body (or its behaviour) that is well designed for life. Modern view: evolution can not only be driven by selection, as Darwin argued, it can also happen by chance if there are two equally good versions of a gene(or a stretch of DNA) and one is luckier than the other during reproduction over the generations==natural selection+genetic drift

Another modern view: random evolution...Natural selection still explains why our bodies have evolved to be well designed, but random evolutionary processes now have an unavoidable quantitative claim on our attention

Second Question

whether the theory explains evolutionary change. In particular, any theory of evolution has to be able to account for the full diversity of life. A theory is inadequate if it only exlains small-scale evolution, or evolution in a different pattern from that seen in life on Earth.

"struggle for existence" Darwin was almost unique in understanding that competition is strongest between individuals within a population, rather than occuring between races, or species. As we shall see in the next chapter, this led him to his 'principle of divergence' that enabled him to answer his second question about evolution.

Plan

Words and Vocabulary

• descend from/descendants/ancestors

• In particulat

• enable sb. to do sth.

• lead sb. to do sth.

• sb is unique in doing sth.
  

Structure

Using the structure of a speech