Evolution by Natural Selection Chapter 24 Evolution by Natural Selection

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.

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.

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

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

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

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

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