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Natural Selection
Charles Darwin—English scientist
(1831—sailed for 5 years on HMS Beagle)
Studied fossils and collected biological specimens
On the Galapagos islands Darwin studied many plants and animals, but
specifically a type of bird—finches.
*He discovered the birds had changed due to isolation on each island, and had
evolved different traits to meet survival needs of each island (ex: beak size,
coloration, wing span, etc.)
*He proposed the idea of Natural Selection
NATURAL SELECTION—a mechanism for change in a population
-Occurs when organisms in a population with favorable variations survive,
reproduce and pass their variations to the next generation
*Darwin’s theory proposes adaptations in species develop over many generations
Ex: mole rats live underground and are blind. They once had site, but over
time, blindness was naturally selected for since it was a disadvantage
*Most structural adaptations develop over millions of years (this is a SLOW
VESTIGIAL STRUCTURES: body structure in a present-day organism that no longer
serves its original purpose, but was probably useful to an ancestor ex: (a whale’s
pelvic bone, a human’s appendix)
Mechanisms of Evolution:
a change in a population over time
(evolution is often a result of natural selection)
GENE POOL: all the alleles of the population’s genes together (due to
possibilities of breeding )
*sometimes a gene pool in a population is limited due to a population being
separated due to environmental changes (ex: a highway being built through a
forest, etc.)
SPECIATION: the evolution of new species when members of a similar population
no longer intrebreed to produce fertile offspring with their natural environment
*This is what happened with Darwin’s finches on each separate island, they
became so different, they eventually became a new species of finch.
DIVERGENT EVOLUTION: pattern of evolution in which species that once were
similar to an ancestral species diverge or become increasingly distinct/when a
population changes
CONVERGENT EVOLUTION: occurs when unrelated species occupy similar
environments in different parts of the world / a pattern of evolution in which
distantly related organisms evolve similar traits