Evolution

Evolution

• Change over time

• Theory that modern organisms descended from ancient organisms due to how they have changed over a long period of time

• Charles Darwin is credited for this theory

Types of Evolution

• Microevolution – changes that occur over a relatively short amount of time– Ex: Peppered moth

• Macroevolution – changes that occur over a relatively long amount of time– Ex: Galapagos finches

• Megaevolution – theory that every living organism has one common ancestor

Peppered Moths

Charles Darwin

• Traveled to various places around the world (Galapagos Islands, Argentina, Australia) and made observations about the organisms and environments (ecosystems) he saw

Galapagos Islands

• Had different species of finches and tortoises

• The different species of finch evolved from same ancestor

• The different species of tortoise evolved from same ancestor

Galapagos Finches• Group of finches traveled from mainland

(Equador) to Galapagos Islands• Ate mainly one food source• One food source not enough for all finches and

their offspring• Different finches adapted to various food

sources (insects, nuts, fruit, berries, nectar from flowers, etc.) and migrated to different islands to look for those food sources

• Different species of finch have different sized beaks due to the food sources they eat

Galapagos Tortoises

• Evolved similar to finches• Group of tortoises traveled from mainland to

islands• Group eventually separated and went to

different islands• New species of tortoises resulted from the

subgroups mating within their own groups• Evidence – different species have different

shaped shells

Darwin’s Observations

• Darwin noticed that although some of the places that he visited had similar environments (similar ecosystems) but had different organisms (plants and animals)– Ex: Argentina and Australia

• Similar ecosystems (grasslands)

• Australia had kangaroos but no rabbits

• Argentina had rabbits but no kangaroos

• Although Argentina and Australia have similar ecosystems, why are some organisms in one place but not the other?

Darwin’s Evidence for Evolution• Fossil record

– fossils of ancient organisms resemble present day organisms

• Geographic distribution of living organisms– similar but unrelated organisms in similar

environments• Homologous structures

– Structure of a body part is similar in another organism, but its function may be different

• Similarities in development– embryos of many animals are similar – organisms have same embryonic tissues but

different mature forms

Homologous Structures

Similarities in Development

Human Embryo Dog Embryo Cat Embryo

Chimpanzee EmbryoWhale Embryo

Natural Selection

• Fitness – ability of an organism to survive and reproduce

• Survival of the fittest – organisms that are best adapted to their environment and will have the best chance to survive and reproduce– Ex: a fast fox will have a better chance of survival

than a slow fox (fast fox should be able to catch more prey than the slow fox)

• Adaptations – inherited traits that increase an organisms chance of survival

Genes and Variation

• In genetic terms, evolution is any change in gene (alleles) frequencies in a population over time

• Populations have a gene pool– Gene pool – all the genes (and their alleles) in a

population

• Relative frequency – how often a gene occurs in a population– Ex: how often the gene for brown fur appears in a

population of mice

Genes and Variation Cont’d…

• Main sources of genetic variation– Mutations – change in DNA sequencing

– Gene shuffling – different combinations of genes are produced during gamete (sex cell) formation

• Phenotypes for a trait determined by how many genes control the trait– Single gene trait – trait controlled by one gene

– Polygenic trait – trait controlled by multiple genes

Evolution as Genetic Change

• Hardy-Weinberg Principle – allele frequencies in a population stay the same unless one or more factors change the frequencies– For evolution to occur, at least one of these factors

MUST NOT happen:• Random mating

• Large population size

• No migrations

• No mutations

• No natural selection

Speciation

• Speciation – formation of a new species• Populations must become reproductively

isolated from one another for a new species to evolve– forms of reproductive isolation

• behavioral isolation – populations have different reproductive behaviors

• geographic isolation – geographic barriers

• temporal isolation – populations reproduce at different times

Speciation of the Galapagos Finches

• Speciation of Galapagos Finches occurred by:– Founding a new population– Geographic isolation– Changes in new population’s gene pool– Reproductive isolation– Ecological competition