Evolution Change in the heritable genetic traits of

Evolution: Change in the heritable (genetic) traits of a population over time Note: when we discuss evolution, we are talking about populations changing, not individuals

Natural selection: The main mechanism by which evolution occurs

4 Conditions for Natural Selection: 1. Variation: Individuals in a population are not identical to each other. 2. Inheritance: Traits are passed to offspring; traits have a genetic basis 3. Environmental population limits: Environmental limiting factors prevent all individuals from surviving to reproduce; some die young.

4. Environmental selection: • Individuals in the population with more favorable (advantageous) traits are the ones that survive to reproduce. • Individuals without advantageous traits die before reproducing. These factors result in a change in the average trait of the population… Biologists call this EVOLUTION!

1. VARIATION Members of a population have traits similar to the average trait of the entire population, but they are not identical. YOUR TURN: Using height as an example, sketch a graph to represent the statement above. Mean (average) height Frequency • Height (cm)

2. INHERITANCE • DNA determines the traits of individuals DNA m. RNA protein trait • Individuals inherit DNA from their parents • This causes the traits of the offspring to resemble the traits of the parents

3. ENVIRONMENTAL POPULATION LIMITS Population A. For all species, if every individual born into a population were to reproduce, the population would grow exponentially Time

3. ENVIRONMENTAL POPULATION LIMITS Population B. Environmental factors (limiting factors) prevent the majority of individuals from surviving to reproduce Time

4. SELECTION g T di hes e e wi in th di ou vid t r ua ep ls ro du cin • Individuals without advantageous traits die before reproducing. Individuals with advantageous traits survive to reproduce. Frequency • These individuals survive to reproduce Characteristic

Populations change, not individuals These individuals survive to reproduce Characteristic n. ge th 50 ra ge , av e av rag e e av rag , 1 st er e, g ag 2 n en e, d. 3 r ge d n. ge n. T di hes e e w. T in di ihtheos div e ue id wi t irn ua th edpi ls ou vroid t r duua ep clis ro ng du cin g Frequency • The “average” characteristic or other measure of the population changes over generations

The environment is the selective force behind evolution • The environment determines what characteristics are “favorable” • Because the environment changes over time, the characteristic that is more favorable for a population changes • Therefore, characteristics of the population change, or evolution occurs

Evolution of Peppered Moths Dark form Peppered form

Explain the evolution of color in the peppered moth population. 1. Describe what trait evolved. 2. Describe how each of the 4 conditions for natural selection exists in the moth example: 1. 2. 3. 4. Variation Inheritance Population limits Selection

• The population of peppered moths became darker in color near industrial areas. • Originally, some moths were dark, some moths were peppered (light). • Color is determined by genes inherited from parents. • Not all moths survive to reproduce- some are eaten by birds. • Pollution killed lichen and made the environment darker, so darker moths were better camouflaged and not eaten as much as peppered (light) moths. • This caused the average color of the moth population to become darker