Evolution

IB 5.4

Evolution: Introduction

• Evolution: cumulative change in the heritable characteristics of a population– Descent with modification– Occurs in populations of a species, not an individual– Result of different selection pressures

• Conditions necessary for change:– Variation: Members of a species show variation– Overproduction of offspring: Populations tend to produce

more offspring than the environment can support– Change in environmental conditions

Natural Selection

Overproduction of Offspring

Variation of traits within the population

Individuals who traits give them higher probability of

surviving & reproducing leave more offspring

Unequal ability of individuals to survive & reproduce leads to

accumulation of favorable traits in

population

Variation: Where does it come from?

• Sex!• Meiosis: Genetic Variation– Crossing Over– Genetic Recombination– Random Fertilization

Overproduction of Offspring

• What happens when there are too many babies?

Overproduction of OffspringWhat happens when there are too many babies?

Lots of resources available,

population increases

Population reaches carrying capacity of

environment

Population continues to

increase, too many individuals

Variation exists within

population, some better than

othersWeaker individuals perish, don’t pass

on traits

STRUGGLE FOR SURVIVAL

Natural Selection

• Overproduction of Offspring + Variation + Inheritance + Competition+ Time = Natural Selection

Images taken from UC Berkley Evolution Site: http://evolution.berkeley.edu/evolibrary/article/bergstrom_02

Evidence for Evolution: Fossil Record

• Fossil record provides history of life on earth

• Shows similarities and differences & indicates relatedness of present day and extinct organisms

• Indicate formation of new species

Evidence for Evolution: Selective Breeding

• Process of humans purposefully breed wild organisms to produce offspring with most desired traits

Evidence for Evolution: Homologous Structures

• Many organisms share structural similarities• Homologous Structures• Analogous Structures

Evolution in Action: Example 1

• Stickleback Fish in Loberg Lake, Alaska changed from fully armored to low armored in 13 generations after environmental change (caused by humans)

Source: http://www.nature.com/news/stickleback-genomes-reveal-path-of-evolution-1.10392

Evolution in Action: Example 2

• Antibiotic Resistant Bacteria

Images taken from UC Berkley Evolution Site: http://evolution.berkeley.edu/evolibrary/article/bergstrom_02

Evolution in Action: Example 3