Evolution change over time Populations evolve not individuals

Evolution – change over time • Populations evolve not individuals • Adaptations – Inherited traits that enhance survival and thus reproduction in a particular environment • Charles Darwin – Theory of Evolution • Based on many observations

Path to Darwin’s Theory 500 BC 322 BC ~2000 yrs old 1700 s 1809 1830 1831 -1836 • Similar idea: simpler forms of life preceded more complex forms from ancient Greeks (2500 years ago) • Aristotle believed that species are fixed – Judeo-Christian thought (book of genesis) • Divine creator; earth to be 6, 000 years old • Early fossil studies; extinct spp. ; earth may be older • Lamarck: inheritance of acquired characteristics • Lyell: Geologist; gradual change by nat. forces • Darwin’s voyage

• Charles Darwin: British naturalist born 1809 – expanded on some existing ideas • • Geologists, naturalists, and scientists Did not address origin of life, but rather focused on explaining the vast diversity of life – provided supportive evidence; 5 year voyage around the world 1831 -1836 – Galapagos Islands • • Wrote essay on evolution based on his observations/experiences 1844 Published “On the Origin of Species” 1859; under competition by Wallace – Descent with modification: ancestral species could diversify into many descendent species by accumulation of adaptations to environment – Hypothesized natural selection as driving force

What is natural selection? • • Over production of offspring Limited natural resources Heritable variations Differential or unequal reproductive success Offspring w/in a varied population, whose characteristics best adapt them to the environment are most likely to survive and reproduce • more fit individuals leave more offspring than less fit individuals

• with so much diversity in just a few thousand years…

• even more diversity over thousands of generations – With natural selection over vast time allows for changes to accumulate

Evidence for evolution • Fossils: preservation of dead organic matter 35 mya examples: 1. 5 mya 375 mya 190 mya 40 mya 5, 500 ya

Fossil record • Layers of sediments • Deposits pile up over millions of years forming strata • Young on top; older on bottom – Read the layers – compare preserved fossils – track changes over time

Is Earth 6, 000 years old or 4. 6 billion? • Radiometric Dating – Dating geologic structures by rate of radioactive decay • Atomic elements decay at a fixed rate – Half-life = time it takes for half of an element to decay – C 14 or radiocarbon dating (plants and animals) • unstable carbon isotope, 5730 years to decay half of a sample • C 14 : C 12 ratio is half in fossil than atm = 5730 • If C 14 : C 12 ratio is ¼ of atm = 11, 460 – K 40 has half life of 1. 3 billion years • Famous tests: – Iceman (Italy, 1991); dated to 5500 years old – Shroud of Turin; evidence shows to be about 700 years old rather than 2000 years old Dr. Willard Libby – Atomic physicist – Nobel Prize for C 14 dating work. Before that, was a key researcher in the development of the atomic bomb.

Comparative anatomy & embryology • Homology – Similarities in form and structure from common ancestory • E. g. mammal forelimbs with different functions • Similar embryological stages – Common structures during similar early development (e. g. , gill slits)

Molecular Biology • Hereditary background and proteins encoded in DNA – Compare gene sequences • Similar sequences – more recent ancestor • More dissimilar – more distant ancestor

Why is evolution the best explanation to the vast natural diversity? • Mountains of evidence of various types – e. g. fossils, radiometric dating, comparative anatomy & embryology, molecular biology • each agrees with the other • provides tremendous support of evolution theory… – disagreement would be falsifiable evidence • Theory still challenged – Theory guess or based on any belief – Theory = falsifiable idea supported by extensive evidence • Theory of Gravitation, Theory of Relativity…principles based on facts (e. g. earth is round)

Populations evolve • Although natural selection acts on individuals, which affects survival & chances to reproduce w/in an env. , a population changes over time • Population genetics – Darwin’s and Mendel’s ideas together – Populations change genetically over time • Gene pool – All alleles in a population • Microevolution – Change in allele frequencies over time – e. g. pesticide resistant allele will increase while its alternate decreases frequency

Agents of potential changes in allele frequency • Natural Selection – pesticide example • Non-random mating – Plants closer to each other may get fertilized – People sometimes choose similar mates (short couples…) • Mutation - creates new alleles • Gene flow – gain or loss of alleles in a popln. – Immigration or emmigration • Genetic drift – change in gene pool due to chance – Founder effect – colonization of small group – Bottleneck effect – reduction of population

Genetic drift – bottleneck effect Drastic reduction of popln. size – Earthquakes, floods, fires, etc – Surviving popln has underrepresented alleles e. g. elephant seals were hunted down to 20; restored now to 30 k; found only 1 allele in ea. of 24 genes; no variation

Selection pressures • A particular phenotype selected for or against depending on the environment • Guppy example: – 2 forces of natural selection working against each other: mate preference and predator vulnerability – Balance where females are attracted to males with brighter colored tails; risk of attracting predators ♀ ♂ – How could you test these selection pressures?

• Observe many generations… • In predator-free environment? – More brightly colored males with large tails evolved • Re-introduced predators – Less flashy males became more “fit”

Natural selection affects populations • Affects the distribution of phenotypes – Normal distribution of varied fur frequencies • Stabilizing selection – Reduces extremes; favors intermediates – Most common

• Directional selection – Acting against one extreme or environment favors one extreme – e. g. darker landscape or, insects exposed to pesticides

• Disruptive selection – Environment is varied to favor both extremes – e. g. patchy landscape with light soil and dark rocks