Chapter 8 evolution basics

What is evolution?

• Evolution- the change in the genetic makeup of a population over time by passing useful or harmful traits to the offspring
• Common ancestry- closely related organisms all descended from a common ancestor
• Descent with modification- living organisms have descended with adaptation from ancestral species

Galapagos Finches(aka Darwin's Finches)

• Finches from the mainland were blown away to other islands
• They developed adaptations-heritable traits that increase an organism's ability to survive and reproduce
• Over many years, new species were formed(speciation).
• *Evolution is NOT organisms individually adapting to their environment.

How does evolution work?

• Natural Selection- organisms with traits that better allow them to survive or reproduce will leave more offspring than their peers
• 3 key principles:
• Parents pass on heritable traits to offspring(reproduction and inheritance)
• Not all offspring produced will survive(competition for resources)
• Offspring vary in traits(variation- can give an advantage in survival and reproduction)

Natural vs. Artificial Selection

• Nature "selects" organisms to survive and reproduce(ex: polar bears, giraffes, etc.)
• Humans can choose/select organisms that will survive and reproduce(ex: corn, dog breeding)
• -Those that are selected are not necessarily the best adapted to the environment

Influences

• Variation- differences in traits
• - This could mean differences in alleles:
• Mutations(random; must be heritable for it to affect evolution whether it is harmful or helpful)
• Sexual Reproduction(crossing over and independent assortment; also random)
• Fitness- how well an organism can survive and reproduce(NOT random)
• High fitness = more offspring
• Low fitness = less offspring
• *If a trait improves fitness, it will usually become more common.

Phylogenetic Trees & Speciation

• Phylogenetic trees show how closely related species are.
• The more closely related = shared a recent common ancestor
• Clades are groups in trees made up of ancestor and all their descendants
• Phylogenetic trees are created based on information from physical anatomy, DNA, and fossils
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