I. Natural Selection Who Lives Who Dies

A. Darwin Proposed 2 Things Evolution occurs Evolution occurs due to Natural Selection

Who do you think chooses who sticks around and who doesn’t? The Environment

The environment chooses which organisms will survive and reproduce based on their phenotype                                                                 

Steps to Natural Selection

Variation is the raw material for natural selection a. Within a population there is a variation in traits (phenotypes)

Living things face a constant struggle for existence a. Produce more offspring than there is room and food for, so they must compete to survive

Only some individuals survive and reproduce a. Some individuals are more “fit” for the environment or for life in general ex. Resistance to disease

4. Natural selection causes genetic change

a. Each generation consists of individuals with traits(phenotypes) that made them more “fit”, so over time, alleles for those traits will increase in frequency

Species adapt to their environment a. selection tends to make organisms better suited to their environment

C. Lethal genes are kept in the gene pool if in the heterozygous form because those individuals will not show the lethal phenotype