Download or evolution

Darwin’s Theory of Evolution
Theory vs. Hypothesis
• Theory: unifying idea which is proven
through repetitious experimentation
• Hypothesis: conjectures or plausible
explanations that may be testable
• Evolution is a theory and not a hypothesis.
Jean Baptiste Lamarck
• Part of why Darwin’s
theory of evolution was
controversial is that
many people still
confuse Darwinian
evolution with
Lamarckian evolution.
• Lamarck’s ideas about
evolution are considered
to be unsound.
Use and Disuse
• Lamarck believed that
if a behavior is useful
and beneficial to the
organism, then the
body parts used to
carry out the behavior
become prominent
and developed.
Example: Giraffe’s have long necks because they
needed the longer necks in order to eat leaves from
trees.
Use and Disuse
• Example of disuse:
Horses and cows eat
grass from the ground
and therefore do not
use their necks in
feeding. This is why
horses and cows
have short necks.
Inheritance of acquired traits
• Lamarck believed that
organisms can inherit
acquired traits from
parents.
• Example: When Arnold
Schwarzenegger has
kids, his kids will come
out looking like him.
Influence of Thomas Malthus
• 1798, economist
Thomas Malthus
published a work
describing the nature
of population growth.
• Populations that
continue to grow
exponentially will
eventually run out of
resources.
Effect of Competition on Population Growth
• Darwin observed
that few species
are overpopulated.
• Competition for
resources and
limitations on birth
rate must select
out some
individuals.
Influence of Artificial Selection
• Darwin also observed
that for the time of
human existence,
humans have
selected plant and
animal traits which
benefit mankind.
• Ex: dog
domestication,
increased crop yield
per plant
Many of Darwin’s
conclusions were
based on
observations of
wildlife in the
Galapagos Islands.
The Galapagos
Islands lie 500 miles
west of Ecuador in
the Pacific Ocean,
directly on the
equator.
“Galapagos” means turtle.
In particular,
Darwin observed
something odd
about the
finches: they all
looked like a
bird he had seen
on the South
American
continent.
Darwin wondered if the birds and other
animals had been created to match their
environment, why didn’t these birds look like
the birds of the African continent, since the
environments of both the Galapagos and
Africa were similar.
Darwin guessed that
some of the birds
from South America
migrated to the
Galapagos.
Once on the islands,
the birds must have
changed over the
years.
large ground
finch
woodpecker
finch
cactus finch
This would explain the numerous species of
birds present.
Darwin concluded:
Each species has descended, with changes,
from other species over time.
Darwin called this…
Descent With Modifications
or
(change in species over time)
Darwin’s conclusions
• Earth is very old.
• Events observed today must have also
happened in the past.
• Organisms struggle for resources and
mates.
• Some organisms are better competitors
than others.
• Traits can be selected.
Natural Selection
• The forces of nature create a selective
pressure so that traits which are better
adapted in a particular environment
enable the organisms within a population
to survive to reproductive age.
• The ability to reproduce is called fitness.
• Alfred Wallace coined the term “survival
of the fittest.”
Effect of Natural Selection on Populations
• The organisms selected and survive to
reproductive age are more likely to pass
on their genes and influence the gene
pool then those than die before mating.
Descent with modification
• With sexual reproduction, each generation
inherits genes that are varied from the
previous generation. These descents are
modified from the parental generation.
Observations &
Inferences on Darwin's
theory of natural
selection
1. Organisms produce more offspring than can
survive. Many that survive do not produce
offspring.
The female green sea turtle lays a clutch of about
110 eggs. She may lay several clutches.
It is likely that less than 1%
of the hatchlings will ever
reach sexual maturity.
Observations & Inferences
on Darwin's theory of
natural selection
• #2. Genetic variation exists within
members of the same species.
Observations & Inferences
on Darwin's theory of
natural selection
• #3. Natural resources are limited.
4. Since more organisms are produced than can
survive, there is competition (struggle for
existence).
Competition exists WITHIN and AMONG species.
Within and Among Species for
food
water
shelter
space
And Within a Species for
mates
Observations & Inferences
on Darwin's theory of
natural selection
• #5. Organisms that have an adaptation
that gives them an advantage have a better
chance to survive and reproduce. Much of
the variation is heritable
Descent with modification: Living species today
are descended with modifications from common
ancestral species that lived in the past.
Characteristics of fit individuals
increase in a population over time.
Over time, genes for less
favored characteristics will be
eliminated from the gene pool.
Example: giraffes and their
increasingly longer necks.
Natural Selection: Survival of the Fittest
An adaptation is any inherited characteristic (a
genetic variation) that can increase an
organism’s chance of survival.
variation exists
An the
organism
doesfirst.
not change
because of need or desire to
the environment changes.
survive. The organism either
already
hasmay
thegive
variation
that
a variation
an advantage
toenables
survive environmental
change.
it to survive
or it dies.
Evidence of Evolution
• The main evidence that supports evolution
is the fossil record.
• The fossil record shows how organisms
have changed over time, and how new
groups have formed – examples of
intermediates between fish and
amphibians, reptiles and birds, and
reptiles and mammals.
Evidence for evolution
• Fossils showing extinct and transitional
species
Cooksonia, earliest
evidence of
branching plant
Evidence for evolution
• Gene and protein comparisons
Evidence for evolution
• Homologous structures –different functions
similar structure – common ancestor
• Analogous structures – different structure
same function – indicates similar pressure
Evidence of Evolution
• Vestigial Structures
– structures that are
reduced in function
and importance.
Examples include
appendix in humans,
toes in snakes, and
hip bones in whales.
Evidence for evolution
• Embryology
Speciation
• If one population becomes isolated and
inbreeds, their gene pool becomes
smaller.
• This population may not be able to breed
with another population of the same
species, thus leading to speciation
(evolution of new species).
Debate over Evolution
• Many people confuse Darwin’s ideas
with Lamarck’s ideas.
• People proclaim that to believe in
evolution is to disregard God.
• Darwin does not propose how man came
to be but how all organisms have the
capacity to change.
• We know today that mutations and
genetic recombination can lead to
differences in DNA from one generation
to the next, making some organisms
better adapted to the environment than
others.