Darwin Presents His Case Darwin waited 20 years

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Darwin Presents His Case

Darwin Presents His Case

 • Darwin waited 20 years to publish his ideas • 1858 Darwin read

• Darwin waited 20 years to publish his ideas • 1858 Darwin read Alfred Russel Wallace’s essay, Wallace’s thoughts were almost identical to Darwin’s • 1859 published On the Origin of Species

The Struggle For Existence • More individuals are produced than can survive • Members

The Struggle For Existence • More individuals are produced than can survive • Members of a populations must compete to obtain – Food Struggle for – living space existence – other necessities of life Who wins?

Variation and Adaptation • Individuals have natural variations among their traits • Darwin hypothesized

Variation and Adaptation • Individuals have natural variations among their traits • Darwin hypothesized that some of those variants are better suited to life in their environment than others. – Predators that are faster or have longer claws or sharper teeth can catch more prey – Prey that are faster or better camouflaged can avoid being caught

Adaptation • Adaptation = any heritable characteristic that increases an organism’s ability to survive

Adaptation • Adaptation = any heritable characteristic that increases an organism’s ability to survive and reproduce in its environment – Body structures: tiger’s claw – Colors: camouflage or mimicry – Physiological functions: photosynthesis – Behavior: avoidance

Mimicry

Mimicry

Camouflage: scorpion fish

Camouflage: scorpion fish

Defensive behavior

Defensive behavior

Survival of the Fittest • Fitness = describes how well an organism can survive

Survival of the Fittest • Fitness = describes how well an organism can survive and reproduce in its environment High Fitness Low Fitness Adaptations well Characteristics not suited to environment well suited to environment Survive and reproduce Die without reproducing or produce few offspring

Survival of the Fittest • Survival is not just staying alive • In evolutionary

Survival of the Fittest • Survival is not just staying alive • In evolutionary terms, survival means reproducing and passing adaptations on to the next generation

Natural Selection • Darwin named his mechanism for evolution natural selection because of its

Natural Selection • Darwin named his mechanism for evolution natural selection because of its similarities to artificial selection • Natural selection = the process by which organisms with variations most suited to their local environment survive and leave more offspring

Natural Selection • Both natural and artificial selection: only certain individuals in a population

Natural Selection • Both natural and artificial selection: only certain individuals in a population reproduce • Natural selection: the environment, not the farmer, influences fitness

Natural Selection • Natural selection occurs in any situation in which more individuals are

Natural Selection • Natural selection occurs in any situation in which more individuals are born than can survive (the struggle for existence), there is natural heritable variation (variation and adaptation) and there is variable fitness among individuals (survival of the fittest)

Natural Selection • Well adapted individuals survive and reproduce • From generation to generation,

Natural Selection • Well adapted individuals survive and reproduce • From generation to generation, populations continue to change as they become better adapted, or as their environment changes • Natural selection acts on inherited traits- only characteristics that parents can pass on to offspring

Natural Selection • Natural selection does not make organisms “better” • Adaptations don’t have

Natural Selection • Natural selection does not make organisms “better” • Adaptations don’t have to be perfect- just good enough to enable an organism to pass it genes to the next generation • Does not move in a fixed direction- no one perfect way of doing something

Natural Selection • Process that enables species to survive and reproduce in a local

Natural Selection • Process that enables species to survive and reproduce in a local environment • If local environmental conditions change, some traits that were once adaptive, may no longer be useful, and different traits may become adaptive • If environmental conditions change faster than a species can adapt, the species may become extinct Dark moths on light colored bark are easy targets for hungry birds but are hidden on pollution darkened trees.

Common Descent • Natural selection depends on the ability of organisms to reproduce and

Common Descent • Natural selection depends on the ability of organisms to reproduce and leave descendants • Every organism alive today is descended from parents who survived and reproduced. Those parents descended from their parents and so on…

Common Descent • Well adapted species survive over time • Darwin proposed that over

Common Descent • Well adapted species survive over time • Darwin proposed that over many generations, adaptations could cause successful species to evolve into new species • Descent with modification = living species are descended with modifications from common ancestors • Implies that life has been on Earth for a very long time