Transcript Darwin and Mechanisms of Evolution

Darwin and Mechanisms of
Evolution
The theory and why it works
Evidence of Evolution: The
Fossil Record
• Indicates life began 3 bya
• Prokaryotes then Eukaryotes then
multicellular Eukaryotes
• Fossil record determines:
• When species appeared
• The type of environment
• When/if species became extinct
What does the theory of evolution
say?
• Theory b/c lots of evidence
• Tested and re-tested by many
scientists
• States that:
• Variations in individuals can lead
to changes in whole species
Natural Selection: The Idea
Behind the Theory
• Evolution controlled by NATURAL
processes
• THE PROCESS IS:
LIVE
+ BREED
+ PASS ON GENETIC INFO
= SURVIVAL OF SPECIES
• “Survival of Fittest”
• Those best ADAPTED will be able to DO THE
PROCESS
Results of Natural Selection
• Short term result:
• Best fit (adapted) will pass on GOOD genes
to offspring
• Long term result:
• Change in frequency (number) of certain
traits
• Which do you think will increase in
frequency GOOD OR BAD?
GOOD OF COURSE!
• As more individuals have good trait,
species is evolving
What drives evolution?
Interactions btw individuals and the
environment:
1. OVERPRODUCTION
2. STRUGGLE FOR SURVIVAL
3. GENETIC VARIATION
4. SELECTION BY THE
ENVIRONMENT
Evolution Cause #1:
B. OVERPRODUCTION
• POTENTIAL TO PRODUCE MORE
OFFSPRING THAN WILL SURVIVE
• This means the best “fit” individuals
will survive, grow and reproduce.
• EX: DEER, FISH
Evolution Cause #2:
C. STRUGGLE FOR SURVIVAL
•
Overproduction leads to STRUGGLE
within species:
1. Only some live to reproduce
2. Competition for resources
3. Best competitors will live and breed
• Must STRUGGLE with environment also
(disease, predators, temp changes etc)
• Those that withstand will survive!
Evolution Cause #3:
D. GENETIC VARIATION
• Variation must exist within survivors
• Ex: Longer legs, bigger claws, diff. fur
color
• Favored traits will stay in pop’n and lead
to evolution
• Adaptive Value:
• Describes a trait that helps an individual
survive in a particular environment
• EX: polar bears have black skin; the black
skin has adaptive value b/c it helps them
survive
Evolution Cause #4:
E. SELECTION BY ENVIRONMENT
• Traits w/ adaptive value benefit those
individuals
• If reproduce, offspring have traits too
• Eventually, # of individuals with trait
increases, and most all will have it!
• Therefore, adapting to environment
DRIVES EVOLUTION!
Evolutionary Trees: Animals
= COMMON ANCESTOR
Comparison of Human and Chimp
Chromosomes
Actual Cartoons from Scope’s
Trial, 1925