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Darwin & Evolution by Natural Selection
Insect eaters Bud eater Seed eaters Cactus eater Warbler finch Tree finches Ground finches
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Geographic Distribution of Living Things
Evidence of Evolution The Fossil Record Geographic Distribution of Living Things Homologous Body Structures Similarities in Early Development
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Charles Darwin Proposed a way how evolution works
How did creatures change over time? by natural selection Collected a lot of evidence to support his ideas British naturalist What did Darwin say? What evidence supports Evolution by Natural Selection? What impact did Evolution have on biology?
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Voyage of the HMS Beagle
Invited to travel around the world (22 years old!) makes many observations of nature main mission of the Beagle was to chart South American coastline After graduation Darwin was recommended to be the conversation companion to Captain Robert FitzRoy, preparing the survey ship Beagle for a voyage around the world. FitzRoy chose Darwin because of his education, his similar social class, and similar age as the captain. Darwin noted that the plants and animals of South America were very distinct from those of Europe Robert Fitzroy
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Voyage of the HMS Beagle
Stopped in Galapagos Islands 500 miles off coast of Ecuador The origin of the fauna of the Galapagos, 900 km west of the South American coast, especially puzzled Darwin. On further study after his voyage, Darwin noted that while most of the animal species on the Galapagos lived nowhere else, they resembled species living on the South American mainland. It seemed that the islands had been colonized by plants and animals from the mainland that had then diversified on the different islands
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Galapagos Recently formed volcanic islands. Most of animals on the Galápagos live nowhere else in world, but they look like species living on South American mainland. 800 km west of Ecuador
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Darwin found…many unique species
Many of Darwin’s observations made him wonder… Why? Darwin asked: Why were these creatures found only on the Galapagos Islands?
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Darwin found…clues in the fossils
present day Armadillos Darwin found…clues in the fossils Darwin found: Evidence that creatures have changed over time ancient Armadillo Darwin asked: Why should extinct armadillos & modern armadillos be found on same continent?
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Darwin found: Different shells on tortoises on different islands
Darwin asked: Is there a relationship between the environment & what an animal looks like?
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Darwin found… birds Darwin found:
Finch? Sparrow? Woodpecker? Warbler? Darwin found: Many different birds on the Galapagos Islands. He thought he found very different kinds… Finch? Sparrow? Woodpecker? Warbler?
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But Darwin found… a lot of finches
Darwin was amazed to find out: All 14 species of birds were finches… Finch? Sparrow? Woodpecker? Warbler? But there is only one species of finch on the mainland! Large ground finch Small ground finch Finch? Sparrow? Darwin asked: If the Galapagos finches came from the mainland, why are they so different now? Warbler finch Tree finch Woodpecker? Warbler?
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Adaptation – a trait that helps an organism survive and reproduce
The finches cinched it! different beaks are inherited variations serve as adaptations that help birds compete for food these birds survive & reproduce pass on the genes for those more fit beaks over time nature selected for different species with different beaks Darwin found: The differences between species of finches were associated with the different food they ate. Finch? Sparrow? Woodpecker? Warbler? Darwin said: Ahaaaa! A flock of South American finches were stranded on the Galapagos… Large ground finch Big seed eater Small seed eater Small ground finch Adaptation – a trait that helps an organism survive and reproduce Warbler finch Insect eater Tree finch Leaf & bud eater
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Relationship between species (beaks) & food
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Darwin’s finches Darwin’s conclusions variations in beaks
differences in beaks in the original flock adaptations to foods available on islands natural selection for most fit over many generations, the finches were selected for specific beaks & behaviors Individuals better adapted to their environment will be better able to survive and pass on their genes (traits) to the next generation than other organisms offspring inherit successful traits accumulation of winning traits: both beaks & behaviors separate into different species
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From 1 species to 14 species…
Warbler finch Woodpecker finch Small insectivorous tree finch Large insectivorous Vegetarian Cactus finch Sharp-beaked finch Small ground finch Medium ground finch Large ground Insect eaters Bud eater Seed eaters Cactus eater Warbler Tree finches Ground finches natural selection for best survival & reproduction variation
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Earlier ideas on Evolution
LaMarck evolution by acquired traits creatures developed traits during their lifetime give those traits to their offspring example in reaching higher leaves giraffes stretch their necks & give the acquired longer neck to offspring not accepted as valid
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Darwin’s view of Evolution
giraffes that already have long necks survive better leave more offspring who inherit their long necks variation selection & survival reproduction & inheritance of more fit traits
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Asking Questions is a good adaptation!
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Darwin found… more fossils
present day Sloth Darwin found… more fossils Darwin found: Evidence that creatures have changed over time (extinct) Giant ground sloth Darwin asked: Why should extinct sloths & modern sloths be found on the same continent?
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Galapagos Islands (off coast of S
Galapagos Islands (off coast of S. America) More Differences between organisms on the islands and mainland Iguanas on mainland had small claws which allowed them to climb trees and feed on leaves; on islands had large claws that allowed them to grip wet rock and feed on seaweed
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Misconceptions about Evolution
Evolution does not tell us about how life first appeared on Earth Individuals do not evolve. Only populations can evolve. Not all changes are “good” Changes that happen to a person in their lifetime do not always get passed on to their children Evolution is not a ladder working towards a better species
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Peppered Moth The Peppered Moth is an example of Natural Selection
During the Industrial Revolution the trees on which the moth rested became covered. This selected against the allele for pale color in the population (which were poorly camouflaged from predators) and selected for the dark color allele
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Evolution in Action Peppered Moths
1700’s most moths grey Trees had grey bark Black moths were rare Late 1700’s = Industrial Revolution & black soot clung to trees Grey moths stood out & were eaten by birds Black moths were not eaten as much & survived to reproduce By 1850 all moths were black
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New Species by Geographic Isolation
Group becomes isolated and cannot mate with the rest of its species Evolves different traits and eventually becomes a new species 10,000 yrs ago only Abert squirrel lived in Arizona forests Small group became isolated on north side of Grand Canyon Evolved into the Kaibab squirrel
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Continental Drift After Pangaea species could no longer walk around the world Some became isolated on continents and evolved independently Australia – species isolated for millions of years Species are very unique (many marsupials)
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Natural Selection Darwin’s theory of natural selection can be described in four basic steps: 1. Overproduction 2. Genetic variation 3. Struggle to Survive 4. Successful reproduction
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Over production Organisms often have more offspring than will survive long enough to become adults.
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Every individual has its own combination of physical traits.
Genetic Variation Every individual has its own combination of physical traits. Some of these traits improve survival and other traits lower the chances of survival in it’s environment.
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Struggle to survive Individuals in a population must compete for food, water, living space, and mates.
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Successful reproduction
Organisms must reproduce to pass their genes to the next generation.
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