Chapter 15Section 1 finish

Charles DarwinBorn Feb. 12, 1809

Naturalist

Joined Crew of HMS Beagle, 1831

5 Year Voyage around world

Astounded By Variety of Life

Avid Collector of Flora & Fauna

Common Descent with Modification

Darwin proposed that organisms descended from common ancestors

Idea that organisms change with time, diverging from a common form

Caused evolution of new species

Darwin Left England in 1831

Darwin returned 5 years later in 1836Darwin returned 5 years later in 1836

The Galapagos IslandsSmall Group of volcanic Islands 1000

km West of South America

Very Different Climates

Island species varied from mainland species & from island-to-island species

TortoisesIguanasFinches

Each island had long or short neck tortoises

Darwin’s FinchesFinches on the same island resembled

each other closelyHowever, those from neighboring

islands were different

Available food on each island was different seeds, nuts, berries, insects…Finches had different types of beaks

adapted to their type of food gathering

Darwin’s Observations

• Individuals of a population vary extensively in their characteristics

no two individuals being exactly alike.

• Much of this variation between individuals is inheritable.

Darwin’s Observations

Left unchecked, the number of organisms of each species will increase exponentially, generation to generation

In nature, populations tend to remain stable in size

Environmental resources are limited

Darwin’s Conclusion• Production of more

individuals than can be supported by the environment leads to a struggle for existence among individuals

• Only a fraction of offspring survive each generation

• Survival of the Fittest

Darwin’s conclusions

• Individuals who inherit characteristics most fit for their environment are likely to leave more offspring than less fit individuals

• Called Natural Selection

Natural Selection

Adaptation – A trait that makes an individual successful in it’s environmentEx. Thick fur in winter, longer legs to run

faster

Organisms with best adaptations are more likely to survive and reproduce

Through inheritance, adaptations will become more frequent in the population

Populations may begin to differ when they become adapted to different environments

Darwin’Darwin’s s Theory Theory of of EvolutiEvolutionon

• The unequal ability of individuals to The unequal ability of individuals to survive and reproduce survive and reproduce leads to a leads to a gradual change in a population, with gradual change in a population, with favorable characteristics accumulating favorable characteristics accumulating over generations (natural selection)over generations (natural selection)

• New species evolveNew species evolve

Definition

Evolution - the slow , gradual change in a population of organisms over time