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Evolution by Natural Selection Life’s Natural History is a Record of Succession & Extinction In historical context • Darwin did not originate the idea of evolution!!! 1. English naturalist who proposed the theory of evolution by natural selection 1. Darwin sailed around the world on the HMS Beagle and carefully studied thousands of different plants and animals 1. Most of animal species on the Galápagos live nowhere else in world, but they resemble species living on South American mainland. 800 km west of mainland 1. Galápagos birds a) 22 of the 29 species of birds on the Galapagos are endemic - found only on these islands 2. One particular group… a) at first, he paid little note to a series of small but distinctive birds b) some were woodpeckerlike, some warbler-like, & some finch-like 1. Darwin was amazed to find out they were all finches a) 14 species b) but only one species on mainland of South America - 800 km away c) all presumably originated from mainland Correlation of species to food source Adaptive radiation - divergent evolution in which ancestral species evolve into an array of species to fit a number of diverse habitats. 1. Differences in beaks a) associated with eating different foods b) adaptations to foods available on islands 2. Darwin’s conclusions a) when original South American finches reached islands, adapted to available food in different environments b) over many generations, the finches changed anatomically & behaviorally c) accumulation of favorable traits led to the emergence of different species 1. Finches with beak differences allowed them to… a) successfully feed b) successfully compete c) successfully reproduce d) pass successful traits onto their offspring 1. Evolution is the gradual change in a species, or populations over time, not individuals. 2. Darwin was the first scientist to realize that evolution can work by natural selection. a) Natural Selection – Is a mechanism for change in populations. It occurs when organisms with favorable variations survive, reproduce, and pass their variations to the next generation i. E.g. Thick fur is a favorable trait in cold environments • His theory was simple… (1)Variation exists in natural populations (2)Many more offspring are born each season than can possibly survive to maturity (3) As a result, there is a struggle for existence (4)Characteristics beneficial in the struggle for existence will tend to become more common in the population, changing the characteristics of a species (5)Over time, and given a steady input of new variation into a population, these processes lead to the emergence of new species 1. Darwin referred to all of these factors together as natural selection: a) Variation b) production of more offspring than can survive c) Competition i. for food, for mates & nesting spots, to escape predators d) differential survival based on traits 1. Evolution by natural selection happens in populations, not individuals. A single organism cannot evolve. Populations evolve. 2. Populations evolve because there is variation 3. Variation causes some organisms to be better fit than others. Better fit organisms are more likely to survive and pass their genes to the next generation • Peppered Moth ◆ dark vs. light variants Peppered moth Year 1848 1895 1995 % dark 5 98 19 % light 95 2 81 • Why did the population change? ◆ early 1800s = pre-industrial England • low pollution • lichen growing on trees = light colored bark ◆ late 1800s = industrial England • factories = soot coated trees • killed lichen = dark colored bark ◆ mid 1900s = pollution controls • clean air laws • return of lichen = light colored bark ◆ industrial melanism 1. Artificial Selection: Humans choose individuals with certain traits for breeding 2. After many generations of selection, dramatic evolutionary changes can result i. Dogs ii. Fruits/Vegetables iii. Livestock 1. Adaptations a) Structural b) Mimicry c) Camouflage d) Physiological 2. Fossil Record 3. Comparative Anatomy a) Homologous b) Analogous c) Vestigial 4. Embryological Development 5. DNA Similarities 1. All organisms have adaptations which help them survive in their particular environment 2. Adaptation: a structure or behavior that helps an organism better survive in its environment Evolution of Mole Rats 1. Mimicry: a structural adaptation that enables one species to resemble another species a) E.g. A harmless species might mimic a poisonous one 1. Camouflage: a structural adaptation that allows a species to blend in with its surroundings 1. Many bacteria have evolved resistance to antibiotics in the last 50 years 2. Pests have evolved resistance to pesticides 1. Insecticide & drug resistance a) insecticide didn’t kill all individuals b) resistant survivors reproduce c) resistance is inherited d) insecticide becomes less & less effective 1. Fossil: Any trace of a dead organism a) Fossils show the evolution of species over the past millions of years b) Fossil evidence proves that modern species have evolved from ancient species Archaeopteryx Puijila the walking seal Tiktaalik 1. Homologous structures: Body structures on different organisms that are similar in structure (same bones) and DID evolve from a common ancestor Homologous Structures 2. Analogous structures: Body structures on different organisms that are similar in function but DID NOT evolve from the same ancestor (bird wing and butterfly wing) Moth (insect) Pterodactyl (reptile) Bird Bat (mammal) Analogous Wing Structures 3. Vestigial structure: body structure in an organism that no longer serves its original purpose but was useful to an ancestor (useless wings on the African ostrich) 1. Early in development, human embryos and embryos of all other vertebrates are very similar, which suggests that all vertebrates are related 1. Nearly all organisms have DNA, ATP, and many of the same enzymes 2. The DNA (genes) of closely related organisms looks very similar