EVOLUTION Darwin’s theory of evolution by natural selection – On the Origin of Species – Organisms produce more offspring than can survive (Malthus) 2.Resources are limited 3.Individuals must compete for these resources 4.Variation exists in populations 5.Natural selection – individuals with beneficial traits (adaptations), more likely to survive, leave more offspring “Fitness” - # of fertile offspring produced is the measure 6. Adaptations passed onto next generation

Mechanisms of Evolution Macroevolution – large scale, major change -new trends, new species Microevolution – changes of gene frequencies within a population Genetic variation–raw material for evolution Gene pool – sum of all alleles of all genes of all individuals in a population *A change in gene pool  evolution

Allele Frequencies What can change them? 1. Mutation 2. Migration – immigration or emigration 3. Genetic drift – in small populations - random loss of alleles 4. Non random mating –if only certain individuals mate 5. Selection - artificial (people choose) OR - natural (environment selects) *Natural selection is the most powerful –the only one that  adaptive change

Hardy-Weinberg Principle -If none of above occurs, allele frequencies will not change result is  genetic equilibrium p 2 + 2pq + q 2 = 1 p – frequency of one allele q – frequency of the other p + q = 1 (example on board)

Evidence for Evolution Microevolution examples: -peppered moths -sickle cell anemia + malaria -the lethal sickle cell allele remains in high frequency where malaria occurs -recent changes in finch beaks -guppies (see graphic) Macroevolution examples: -paleontology (fossils) -comparative anatomy : homologies, vestigial structures -embryology -biogeography – convergent evolution -biochemistry – similarities in proteins - nucleotide sequences

Sources of variation in populations Natural selection acts on variation 1.Mutation – only sources of new variation (new alleles) 2.Genetic recombination (sexual reproduction) -crossing over -independent assortment -random gamete joining (fertilization) 3.Diploidy – 2 copies of each gene -can have 2 different forms (alleles) -maintains diversity 4.Symbiosis -endosymbiosis, lichen, etc.

The Origin of Species Speciation, Macroevolution Species – definition? Isolation: -populations become separated (one way or another) -gene pools now isolated -each gene pool changes over time -each population becomes distinct species

Isolating Mechanisms Prezygotic (Pre-mating): 1. Geographical – physical separation 2. Ecological – distinct habitat or niches within region 3. Behavioral 4. Temporal – reproduction occurs at different times 5. Mechanical – mating is physically impossible 6. Prevention of gamete fusion -sperm and egg incompatible

Postzygotic: 1. Embryo dies 2. Hybrid weakness 3. Hybrid sterility

Divergent Evolution 1 species  2 or more species Adaptive radiation: -1 common ancestor  cluster of closely related species eg. Darwin’s finches Placental mammals Hybridization and Polyploidy – can create new species in plants

Types of Selection

Sexual Selection -when one gender (usually males) competes to mate with the other gender -often females choose mates -selection is for (examples): -large body -horns, antlers -colorful plumage -certain behaviors

Primate Evolution Prosimians (40 million years ago): -grasping fingers and toes -binocular vision -lemurs are modern prosimians Apes, monkeys -monkeys – even better vision -opposable thumb -complex social behavior -learning (extended parental care) -large brains -apes – hominoids (15 million years ago) Hominids -humans and extinct ancestors - bipedal, larger brains (extensive use of tools, language)

-Australopithecus -Homo habilis -Homo erectus -Homo sapiens (500,000 years ago)