Download 15-2 Theories of Evolution

15-2 Theories of Evolution
Biological Evolution
Change of populations of organisms over
generations.
Jean Baptiste de LaMarck (1780)
 First to propose a
hypothesis of species
modification.
 Similar species descended
from a common ancestor.
 He said acquired traits
were passed on to offspring.
Acquired traits are traits
which are not determined by
genes but by experience or
behavior of an organism.
These traits cannot be
passed on.
 Baptiste studied the
webbed foot of water birds.
He thought that the offspring
would also have webbed feet
because of acquired traits.
This hypothesis was rejected
but was a forerunner for
evolution.
Charles Darwin came along
50 years later and presented
a better case for evolution.
Jean Baptiste de LaMarck
Charles Darwin (1823-1913)
 Proposed hypothesis that
species were modified by
natural selection.
*Natural selection deals with
genetics. It says organisms
that are best suited to their
environment are best able to
reproduce and have more
offspring.
 He published a book called
“The origin of the species” in
1859 which announced his
hypothesis.
 He was English. He was
hired to go on the H.M.S.
Beagle as a naturalist. This
ship traveled to S. America,
Europe, Australia, and Africa
for 5 years.
During the 5 years, he
collected many different
types of fossils and observed
thousands of species.
Map of Beagle
Charles Darwin
Analysis of Data
Collected 13 similar
but separate
species of finches
from the
Galapagos Islands.
He said they all
came from 1
female finch over
time.
Origin of Species
Took Darwin
21 years to publish
this book.
It was on evolution
by natural
selection.
Darwin’s Finches
Darwin’s Theories
 2 theories
1. Evolution occurs “Descent with
modification”.
2. It is caused by natural selection.
1. Descent with Modifications
 Newer forms in the
fossil records are just
modified forms of
older forms.
 Similar organisms
arise in the same
geographic location.
Organisms give rise
to similar organisms.
2. Modification by Natural Selection
States how evolution occurs.
 Darwin influenced by Thomas Malthus.
 Said that populations could grow unchecked
(meaning they could get bigger and bigger) but
they do not because of deaths due to sickness,
environmental conditions, reproduction rates,
etc. However, some organisms have traits which
help them survive.
Traits
 If it increases the reproductive success and is
inherited then the trait will be passed on to many
offspring
 As favorable genes increase, a population of
organisms will adapt to its environment
 Individuals with highest fitness will adapt well
to its environment and reproduce more
successfully then an individual with low fitness.