Darwinian Evolution

Chapter 1010.2 - 10.5

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Galapagos Islands

Darwin visited the Galapagos Islands He formed his ideas about natural

selection here Why were the Galapagos Islands a

good place to study natural patterns?

Variation – difference in physical traits of an individual from those of the other members in the group

Darwin took note of the variation of organisms via each island in the Galapagos

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Different environments

Long necked and legged tortoises lived in areas with mostly tall plants.

Tortoises with a short neck and legs, lived in areas with short plants and mosses.

Animals could adapt to their environment?

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Adaptation

Adaptation – feature that allows an organism to better survive in its environment

Adaptations can lead to a genetic change in a population over time

Evolution – genetic change in a population over time

So adaptations can lead to ______ ?

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Ancient Earth?

Darwin found fossil evidence of ancient & extinct organisms that were similar but different than currently living (extant) forms.

10.3 – How does Evolution occur?

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Selection

Darwin observed that domesticated plants and animals displayed variation that was not found in their wild counterparts

Through selection of animals with particular traits, breeders could produce a great amount of diversity

Artificial selection – humans select for certain traits, and preferentially breed those animals in possession of those traits Called artificial selection since humans are selecting for

certain traits that they deem desirable

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Heritability

In order for a trait to be selected for, artificial or natural, trait must be inherited

Heritability – the ability of a trait to be passed down from one generation to the next

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Natural Selection

Natural Selection – mechanism by which individuals that have inherited favorable adaptations produce MORE offspring on average than do other individuals

Environment is the selective agent

Characters are selected only if they confer some advantage to those who have it

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Conditions for Natural Selection

Struggle for survival Resources are limited

Space, food, mating opportunities Wants are Unlimited

Organisms can produce more offspring than the environment can provide for

Certain adaptations seemed well-suited for their environment

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4 Principles for Theory of Natural Selection

1. Variation the heritable differences are the basis for natural selection

2. Overpopulation If the population is supported by the environment, no selection

will occur

3. Adaptation Certain individuals have favorable variation that enables them

to be better suited to their environment

4. Descent with Modification Natural selection will result in populations that are better suited

to survival and reproduction in an environment

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VARIATION

OVERPRODUCTION

ADAPTATION

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Imperfect Organisms

Why are organisms not perfectly adapted to their environment?

Natural selection works on EXISTING variation

Natural selection can only modify what is there, so perfect structures are not always possible

Could a human ever be able to lift 18 tons (36,000 pounds)?

Could a human ever be able to develop gills for underwater existence?

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Evidence for Evolution

Fossils Okay

Biogeography Good

Embryology Excellent

Anatomy Excellent

Genomics

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Fossils provide evidence of evolution.

• Fossils in older layers are more primitive than those in the upper layers.

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The study of geography provides evidence of evolution.

– island species most closely resemble nearest mainland species– populations can show variation from one island to another

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Embryology provides evidence of evolution.

Larva

Adult barnacleAdult crab

– identical larvae, different adult body forms– similar embryos, diverse organisms

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The study of anatomy provides evidence of evolution.

Human hand Bat wingMole foot

– Homologous structures are similar in structure but different in function.

– Homologous structures are evidence of a common ancestor.

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Human hand

Bat wing

Mole foot

Fly wing

Analogous structures are not evidence of a common ancestor.

Analogous structures have a similar function.

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• Vestigial structures are remnants of organs or structures that had a function in an early ancestor.

• Ostrich wings are examples of vestigial structures.

Vestigial Structures

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Paleontology provides evidence to support evolution.

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Molecular and genetic evidence support fossil and anatomical evidence.

Two closely-related organisms will have similar DNA sequences.