evolution by natural selection. life’s natural history is a record of succession & extinction
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1. English naturalist who proposed the theory of evolution by natural selection
Charles Darwin (1809 – 1882)
1. Darwin sailed around the world on the HMS Beagle and carefully studied thousands of different plants and animals
HMS Beagle Voyage 1831-1836
800 km west of mainland
The Galapagos Islands
1. Most of animal species on the Galápagos live nowhere else in world, but they resemble species living on South American mainland.
The Birds…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 woodpecker- like, some warbler-like, & some finch-like
Darwin’s finches
1. Darwin was amazed to find out they were all finchesa) 14 speciesb) but only one species on mainland of
South America - 800 km awayc) 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.
Darwin’s finches
1. Differences in beaksa) associated with eating different foodsb) adaptations to foods available on islands
2. Darwin’s conclusionsa) 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 feedb) successfully competec) successfully
reproduced) pass successful traits
onto their offspring
Darwin’s finches
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
Evolution by Natural Selection
Essence of Darwin’s ideas• 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
Natural Selection
1. Darwin referred to all of these factors together as natural selection:a) Variationb) production of more offspring than can survivec) Competition
i. for food, for mates & nesting spots, to escape predators
d) differential survival based on traits
Variation in Populations
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
• 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 resulti. Dogsii. Fruits/Vegetablesiii. Livestock
Evolution by Artificial Selection
1. Adaptationsa) Structuralb) Mimicryc) Camouflaged) Physiological
2. Fossil Record
3. Comparative Anatomya) Homologousb) Analogousc) Vestigial
4. Embryological Development
5. DNA Similarities
Evidence for Evolution
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
Evidence #1 - Adaptations
Adaptations #2 - Mimicry
1. Mimicry: a structural adaptation that enables one species to resemble another species
a) E.g. A harmless species might mimic a poisonous one
Adaptations #3 - Camouflage1. 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
Adaptations #4 - Physiological
Natural selection in action
1. Insecticide & drug resistancea) insecticide didn’t kill
all individualsb) resistant survivors
reproducec) resistance is
inheritedd) 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
Evidence #2 - Fossil Evidence
Evidence #3 - Comparative Anatomy
1. Homologous structures: Body structures on different organisms that are similar in structure (same bones) and DID evolve from a common ancestor
Comparative Anatomy
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)
Comparative Anatomy
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)
Evidence #4 - Embryological Development
1. Early in development, human embryos and embryos of all other vertebrates are very similar, which suggests that all vertebrates are related
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