Transcript Theories of Evolution - South Kingstown High School

Evolution
Modern Humans
Evolution
• Definition:
Change in a
population of
organisms over
time.
• Human evolution
illustrated on a
cladogram
Theories of Evolution
• Jean-Baptiste
Lamarck – 1809
published his theory
of evolution
– Mechanism of
Evolution =
Inheritance of
Acquired
Characteristics
Theories of Evolution
• Charles Darwin – 1859
published his theory of
evolution in the major
work, On the Origin of
Species
– Mechanism of Evolution
= Natural Selection
The Original Manuscript
• Most important book on biology ever
published!
Lamarck’s Ideas
• Organisms change over time
• Organisms are adapted to their
environment
• They are continually changing and
acquiring features more suitable for their
environment.
• Continued 
Larmarck’s Ideas
• During an organism's lifetime, there is
selective use or disuse of its organs
and traits. If a trait isn’t usedit’s lost.
Larmarck’s Ideas
• Traits that are used are passed on to
their offspring. Over time, this process
leads to the change in a species. (hence
the term: inheritance of acquired
characteristics)
Darwin’s Ideas on Evolution
• Variation – organisms show variation in
each of their traits: height, colors of
eyes/hair/skin, resistance to disease, etc.
• Natural selection – Organisms better
suited to their environment survive and
reproduce (also known as survival of the
fittest).
• Fitness – ability to survive and leave
offspring. No offspring = No fitness.
Worksheets
• Natural Selection and
fur color
• Evolution:
comparison of
Lamarck (acquired
characteristics) and
Darwin’s (natural
selection) ideas on
evolution.
Darwin’s ideas on Evolution
• In the early 1800’s, when Darwin was
born, people thought the Earth was a few
thousand years old.
• But by the 1820’s, scientists hypothesized
the Earth was millions of years old.
• 5000 years
• 5,000,000 years
Darwin’s ideas on Evolution
17-11 MYA
5 MYA-present
• An ancient Earth was necessary to
35,000,000YA
support Darwin’s ideas on evolution—
populations change over (long, long
periods of) time.
12-6 MYA
55,000,000YA
Natural Variation in
population of bacteria
Microevolution
according to
Darwin’s Ideas
on Natural
Selection
Macroevolution
according to
Darwin’s Ideas
on Natural
Selection:
Speciation* –
formation of
new species
Genes and Variation
• Most
phenotypes
(traits) are
polygenic.
• A graph of
these traits
often shows a
bell curve.
Stabilizing Selection
• If individuals near the
center of the bell
curve have higher
fitness (= leave a
greater amount of
fertile offspring) then
stabilizing selection
occurs.
Directional Selection
• If individuals at
one end of the
bell curve have
higher fitness
then directional
selection
occurs.
Disruptive Selection
• If individuals at
both ends of the
curve have
higher fitness
than those in
the middle then
disruptive
selection
occurs.
Genetic Drift
• If a small population is isolated from others
of the same species, it is possible that just
be “chance” one allele may become more
common in a population.
Genetic Drift
• For example: The Bronx, NY, becomes
built up and trees are cut down. Few
squirrels are able to survive. However,
one section of the Bronx is set aside for
the development of the Bronx Zoo. Trees
I’ I’m an
are
NOT cut down in this area. By chance,
Eastern
Gray
several
of
the
gray
squirrels
in
the
area
of
Squirrel
the zoo have black fur (a variation in fur
color). Over time, the allele for black fur
becomes common in this population.
How do new species form?
Example: Galapagos Finches
• A small group of a species of finch arrives
on one of the Galapagos Islands
• These finches do not usually fly across
open water—they may have gotten lost or
were blown there by the wind.
Speciation continued!
• Over time these original finches may have
ended up on other of the Galapagos
Islands through some chance occurrence.
• USUALLY the finches do NOT fly from one
island to another.
Speciation continued!
• The Galapagos Islands had different
environments.
– Some had a low elevation and were dry with
little plant material.
Speciation continued!
• Others had a higher elevation with greater
rainfall and many plants.
Speciation continued!
• Directional selection occurs:
– One island may have seeds that are large and
difficult to open.
– Birds with a larger, thicker beak will have the
highest survival rate on this island
Speciation continued!
• Directional selection occurs:
– Another island may have seeds that are small
and easy to open
– Birds with a small, thinner beak will have the
highest survival rate on this island
Speciation continued!
• Reproductive Isolation: if the populations
remain separate, and their gene pools
continue to change, eventually they can no
longer mate with each other—they are
then TWO NEW SPECIES!!!
• On the Galapagos Islands this processes
resulted in the evolution of 13 different
finch species.
Darwin’s
Finches
Evidence of Evolution
• Fossil Record
Evidence of Evolution
• Comparative Anatomy:
– Homologous structures = structures that have
different mature forms but develop from the
same embryonic tissue
Evidence of Evolution
• Vestigial organ = organ that serves NO
useful function in an organism.
– Wisdom teeth
– Appendix
HUMANS
Fingernails on
Seal’s Fin
Embryology
NOTE
Similarity of
embryos of all
of these
animals
Evidence of Evolution
• Similarities and dissimilarities in DNA
code.
• Complete worksheet + bar graph.