L1 Natural Selection Learning Objectives: Describe Darwin’s theory of evolution by natural selection. Analyse the evidence supporting the theory of evolution.

Evolution Evolution = change in species over time Evolution is a fact. There is concrete evidence that species do change over time because of changes in the environment. One theory of evolution states that all organisms have evolved from simple life forms millions of years ago. This theory is highly controversial.

Example: The Peppered Moth http://peppermoths.weebly.com/

Natural selection = process that causes evolution by survival of the fittest All populations contain variety, not all organisms are the same. A change in the environment causes the weakest organisms (those least suited to the environment) to die. Only the strongest (those best suited to the environment) survive and pass on their genes to their offspring (next generation). The new generation’s DNA contain genes for the features that help them to survive. Over many, many generations the DNA (genes) changes to produce big changes in features of the species.

Competition Organisms compete for many things; food, shelter, space. Those with the best features compete more successfully and survive. Survivors reproduce and pass their genes for the more successful features onto their offspring. Over time the small changes in features add up to big changes in the species.

Where do the different changes come from? Mutation = a random change in the DNA (can be caused by an error) Mutations can produce new forms of the genes. These lead to more variety in the populations. Some mutations are harmful but some mutations lead to better features.

Speciation Speciation = the process that forms new species One possible way that a new species forms is if one population becomes geographically isolated from the rest of the species. The new population evolves from natural selection caused by different environmental factors. Over time the two groups become so different they become different species.