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What is gradualism and
punctuated evolution?
Agenda
1. Theories of Evolution Notes
2. Theories coloring worksheet
3. Darwin’s postulates worksheet
History of the theory
• Common among scientists in the early 1800s
• Georges Cuvier – fossils in lower strata are more
different than present-day organisms
• James Hutton – Gradualism: major changes in
Earth’s geologic history due to slow and
continuous processes
• Charles Lyell – Uniformitarianism: those
continuous processes are STILL working today
Jean Baptiste de
Lamarck
• Use and Disuse – the more you use something,
the greater it becomes; the less you use
something, the more it deteriorates
• Inheritance of Acquired Characteristics
– Acquired trait – a trait that arises during the lifetime of an
organism
– Can be passed to offspring
Lamarck
• Organisms acquire traits and then pass these
traits on to their offspring
Lamarck’s Influence
Incorrect
• Not all traits acquired get passed on
Important
• Introduced change over time
• Realized organisms are changing
Charles Darwin
• Naturalist
• Traveled on the HMS Beagle (1831-1836)
• South America, Galapagos Islands, Australia
• Wrote The Origin of Species
Galapagos Islands
• small group of volcanic islands
• no land mammals or amphibians
• Back in England he looked at his findings
– Tortoises and Finches
Tortoises
• Similar BUT tortoises on different islands had
different shell morphologies
– Could tell which island a tortoise came from just
by looking at its shell
Finches
• Finches – collected 13 similar but separate
species of finches
– Each had a distinct bill (beak)
• Observed finches doing very "unfinch-like things"
• e.g. one behaved like a hummingbird, another like a flycatcher,
another like a woodpecker
• Conclusion: an ancestral group of finches
colonized the islands and then, in the absence of
competitors these colonizers gradually changed
into the specialized finches that he saw
– Implied shared common ancestor
People influenced Darwin
• Charles Lyell
• Malthus
– populations can grow exponentially
– the are limited by war, disease, or resources
• This led to Darwin’s idea that there’s a struggle
for existence
Darwin’s Theories
Descent with Modification
• through selective breeding able to dramatically
change domestic species (dogs)
• Over time/generations traits with reproductive
advantages become more common
• All species descended from one or a few original
types of life
Darwin’s Theory
• Natural selection – organisms best suited for
the environment reproduce more successfully
• Over several generations organisms with
favorable traits increase
• Variation within a population
• Traits are inherited/passed on
• More offspring are produced than can survive
• Surviving offspring will be favored by the environment "natural selection“
• Those organisms that survive have favorable variations
(known as adaptations)
• Over time, these favored variations will accumulate -- this is
"descent with modification" or evolution
2 types of Adaptations
• Camouflage and mimicry
Modification by Natural Selection
• An organism’s genetic contribution to the next
generation is fitness
– Greater fitness = better adapted to env’t =
reproduces more successfully
• Favorable traits give organisms an adaptive
advantage
• Environment “selects” traits
– Favorable traits depend on demands of env’t
Summary of Darwin
• Natural Selection – organisms best suited/best
adapted to the environment survive and
reproduce
– Adaptations
• the population is the unit of evolution
– individuals do not evolve during their lifetimes
Theory of Evolution
• Evolution – change in the inherited traits of a
population of organisms over time
– NOT new species arising from pre-existing species
• Part but not all of evolution
• Cheetahs are able to run faster than 60 miles
per hour when chasing prey. How would a
biologist explain how the ability to run fast
evolved in cheetahs, assuming their ancestors
could run only 20 mph?
• A long time ago, some cheetahs were faster than the
others
• The cheetahs that could run faster were able to catch
their prey and were better able to survive
• The slow cheetahs died off, or weren’t able to
reproduce as successfully
• The cheetahs that survived were the ones that could
run faster
How did the heavy coat in polar bears evolve
if their ancestors had thinner coats?
1. A long time ago, some polar bears had
thicker fur than others
2. The thicker coat was favorable
3. The polar bears with thin coats died off.
4. The ones with thicker coats survived and
reproduced.
Peppered Moths