Download Natural Selection - Bakersfield College

Biology 11
Mrs. Garrison
EVOLUTION OF ORGANISMS OVER TIME
HISTORICAL PERSPECTIVE
Concept of evolution, or change, of plant and animal species over time is not
Fossils –
1600, 1700 & 1800s – views of the church
During late 1700’s, however, geologists (primarily in England) were paving the way for a
comprehensive scientific theory on the origins of modern species
James Hutton (1785) – Theory of UNIFORMITARIANISM
Charles Lyell (1830) – age of earth must be in millions of years, not thousands
William Smith (1769-1830) – surveyor
First systematic study of fossils
**SO WE SEE AN EARTH SURFACE BUILT LAYER BY LAYER OVER
COURSE OF TIME & MOLDED BY SLOW PROCESSES OF NATURE
BIOLOGISTS WERE NOT SO READY TO CHANGE, HOWEVER
Among first to suggest that species might undergo changes over time:
Buffon –
Erasmus Darwin (Charles Darwin’s grandfather) –
First person to work out systematic theory of evolution of species:
Jean Baptiste Lamarck – 1801 –French Biologist
INHERITANCE OF ACQUIRED CHARACTERISTICS
Predominate view in early 1800’s was that of Cuvier (1769-1832) –
--excellent understanding of fossils
--staunch opponent of idea of change in species
proposed theory of CATASTROPHISM
NATURAL SELECTION
Charles Darwin - born 1809
studied for medicine & clergy, not inclined towards either
always enjoyed collecting specimens & observing habits of living org's
age 22 (1831) - jumped at invitation to become naturalist aboard HMS
Beagle during a 5-yr. voyage around the world
HMS Beagle traveled from England down east side of South America, up
west side of S.A., across Pacific to New Zealand & Australia,
across Indian Ocean, around Cape of Good Hope & back to England
--major undertaking was to chart coast of S.A.
While there Darwin would spend hours collecting living &
fossil specimens, & observing behavior of local species
Darwin was impressed by the sheer # of diff. spp.
Darwin had read Lyell's book & the idea of a gradually changing physical
environment made good sense.
Back at home, Darwin looked at the evidence and began to see a pattern that
might dev. if spp were to change over time along with the changing
environment
Struggling with a possible mechanism, the answer became clear after
reading Thomas Malthus' "Essay on the Principle of Pop."
Malthus had written that pop's increased at geometrical rate,
eventually running out of food & space
Darwin recognized a tremendous amount of variability within a given spp &
he brought this and Malthus' theory into play in his THEORY OF
NATURAL SELECTION, which provided a plausible mech. for the
change in a spp over time:
1)
2)
3)
4)
5)
THUS, THE ENVIRONMENT "SELECTS" FOR THOSE ORG'S WHICH
ARE BEST SUITED TO IT (NATURAL SELECTION)
An org. is only best fit for that particular environment –
--Thus, spp will slowly change as environ. selects for those
members of pop. which are suited to the environmental
changes.
--If a spp doesn't change to fit environ, it will die out.
--Eventually, the new spp may be very diff. from the original spp.
Evolution does not cause change in individual org. but rather in a
species over time - takes many generations.
ALSO, natural selection does not create new traits. New traits
originate by chance and environment selects for or against
them
AND natural selection does not create whole new, intricate organs all
at once -- each step is a minute change
Darwin's theory of NATURAL SELECTION was essentially worked out in 1838.
HOWEVER, for next 20 years he worked on it (between bouts of illness), wanting
it to be perfect
Alfred Russell Wallace –
Today we know about DNA, chromosomes and genes as the hereditary material. We
recognize that changes in outward traits are due to chance changes
(MUTATIONS) in the genetic material and also new combinations of traits due to
sexual reproduction - that is, an offspring will receive traits from 2 parents in a
combination never before realized.
Darwin did not know about genes & chromosomes, but he recognized that the traits
org's pass on must be inherited, not acquired, as Lamarck thought.
ADAPTIVE RADIATION
On Galapagos Islands, Darwin found 13 diff. spp of finches now believed to have
arisen from one single pair or pregnant female from S.A. mainland