1. Evolution by Natural Selection
Chapter 24
Evolution by Natural Selection

2. Key Concepts
Populations and species evolve, meaning that their heritable characteristics change through time. Evolution is change in allele frequencies over time.
Evolution by natural selection occurs when individuals with certain alleles produce the most surviving offspring in a population. An adaptation is a genetically based trait that increases an individual’s ability to produce offspring in a particular environment.

3. Key Concepts, cont’d
Evolution by natural selection is not progressive, and it does not change the characteristics of the population. Animals do not do things for the good of the species, and not all traits are adaptive. All adaptations are constrained by trade-offs and genetic and historical factors.

4. The Theory of Evolution
Change of allele frequency (heritable traits change over time)
Testable
All species are related by common ancestry
Theoretical

5. Evidence of Evolution - Relatedness
Homology (same)
Genetic: comparing similar DNA and/or Amino Acid Sequence
Developmental: comparing similar embryos
Structural: comparing similar anatomy
Geography:
Comparing two similar species with similar traits
Cause- separation of the species in different environments produce different traits

6. Evidence of Evolution - Static (change)
Fossils
Transitional features
In the fossil record, intermediate traits an organism has that links the traits or two organisms
Example- Lizard -> Lizard with feathers -> Bird
Vestigial traits
Traits that are present that have no use
Example- human tailbone & human goosebumps

7. Natural Selection Survival of the Fittest How does a species survive?
Adaptation:
There is a variety of different traits (genetic variation) in a population
The environment changes
Increased genetic variation helps the population survive in the new environment

8. Evolutionary Limitations
Fitness Trade-offs: an adaptive trait can both help and hurt an organism
Example- big organisms can get food easier but need more food
Genetic Constraints: alleles that affect more than one gene which can both help and hurt the organism
Historical Constraints: traits passed down which can help or hurt the organism