chapter 15 section 1 finish. charles darwin born feb. 12, 1809 naturalist joined crew of hms beagle,...
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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