Theory of EvolutionNatural Selection

Genetic variation is the driving force behind evolution. There are many ideas of why populations change overtime. These changes may be due to mutation, movement of alleles between populations, interbreeding, isolation, and natural selection

Theories of Evolution

A. Jean Baptist LamarckEvolution occurs due to inheritance of ACQUIRED

TRAITS FROM A COMMON ANCESTOR, not from changes in the environment

Idea that variation in a population is created by experience

Ex. Individuals passed on to offspring body and behavior changes acquired during life

What is wrong with this idea?

Theories of EvolutionB. Charles Darwin2 Major Theories:

1. Descent with Modification: stated that ALL new species were ALTERED DESCEDENTS of OLDER ANCESTORS and arose from similar geographic locations

2. Natural Selection: proposes that NATURE or environmental conditions DETERMINE and individual’s CHARACTERISTICS, which in turn leads to EVOLVING population over time

4 Mechanisms of Natural Selection

o GENE VARIATION EXISTS WITHIN A POPULATION

Only if variation is GENETICALLY BASED will natural selection lead to evolution

-MUTATIONS and RECOMBINATION of genes may produce beneficial changes and INCREASE gene variation within a population

o INDIVIDUALS WITH MORE SUCCESSFUL TRAITS WILL PASS TRAITS ON TO OFFSPRING

-in turn, will increase the success of the population

o INDIVIDUALS MOST ADAPTED TO THE ENVIRONMENT WOULD GET THE BASIC RESOURCES FOR LIFE

-ADAPTATION: individuals response to environmental pressures – may reduce competition within a population

o INDIVIDUALS THAT ARE MOST “FIT” HAVE GREATEST POTENTIAL TO REPRODUCE SUCCESSFULLY AND INCREASE POPULATION NUMBERS OVER TIME –”survival of the fittest”

-FITNESS: reproductive success of one individuals genetic contribution to the next generation

Examples of “fitness”• Bacterial resistance to antibiotics

• Pesticide resistant insects

• Skin color - melanin

Summing Up Natural Selection