Transcript Biological Evolution

Biological
Evolution
What is Evolution
• Evolution is descent with
modification
• Microevolution = changes in gene
(allele) frequency in a population
from one generation to the next
• Macroevolution = descent of
different species from a common
ancestor over many generations
Evolution Explained
• NOT simply change over time
– Ex: Life cycle is NOT evolution
• MUST involve DESCENT through GENETIC
INHERITANCE
• Change in a POPULATION over GENERATIONS
of time
• Underlying Concepts:
– All organisms share a Common Ancestor
– Occurs through Natural Selection
Natural Selection
1. Variation in traits: more than one allele for a
trait; one allele may be more advantageous
than another
2. Differential reproduction: NOT all individuals
get to reproduce to their full potential
3. Heredity: adaptations are genetic
4. End result: more advantageous trait allows
individuals to survive and produce more
offspring
Natural Selection
Natural Selection
Natural Selection
Shift in Allele Frequency
• Mutations can produce new phenotypes that
may or may not be beneficial to the organism
• If the new allele is beneficial, then those
organisms will be more “fit” and therefore
better able to reproduce.
• Over generations of time, this will cause the
new allele to become more frequent in the
population.
Fitness
• Fitness = how good a particular genotype is at
leaving offspring in the next generation compared
to other genotypes
• FITNESS is INHERITED!
• Fitness will increase one or more of the following:
– Ability to Survive
– Find a Mate
– Produce Offspring
• Fitness is NOT necessarily strongest, fastest, or
biggest.
• Ultimate Goal = transmit GENES to the next
generation
Sexual Selection
• Special case of natural selection
• Acts on an organism’s ability to obtain &/or
successfully copulate with a mate
• Organisms may go to extreme lengths for sex
– Peacock tail
– Elephant seals fight
– Fruit flies dance
– Some even die for it!
(male praying mantis)
Artificial Selection
• Artificial Selection = people (NOT nature) select
which organisms get to reproduce
• Farmers and breeders commonly cultivate crops
using Selective Breeding
Adaptation
• Adaptation = inherited characteristic in a
population that increases fitness
• Adaptation Types
– Behavioral
– Biochemical
– Anatomical
• An adaptation is NOT ACQUIRED during an
organism’s lifetime
Lamarck = Acquired Traits (wrong)
Giraffes needed longer necks so they “grew” longer necks through
repeated use. THIS IS INCORRECT!
Giraffes that INHERITED longer necks were better able to survive,
so they passed those genes on to their offspring.
Darwin = Inherited Variation &
Natural Selection (correct)
Adaptation
• Functional = Produced by Natural Selection
• Heritable = MUST be able to be INHERITED
(genetic trait)
• Adaptive = increases the fitness of an organism
Speciation
• Species is the biggest “gene pool” possible
under natural conditions.
• If the organisms can breed and produce fertile
offspring, they are the same species.
– German Sheppard + Chihuahua = puppy (fertile)
– Horse + Donkey = Mule (sterile hybrid)
– Horse & Donkey (NOT the same species)
• Speciation produces 2 or more separate
species caused by:
– Geographic Isolation
– Reproductive Isolation
Speciation of Fruit Flies
• A population of wild fruit flies lays eggs on
rotting bananas…
• Disaster strikes: a hurricane washes the bananas
and immature fruit flies out to sea. The bananas
eventually wash up on the mainland. There are
now 2 separate populations of fruit flies that
cannot mate due to location.
• Populations become different due to slightly
different conditions on the island. This causes
a shift in allele frequency in the island
population because of selection pressures.
• So we meet again: If another storm reintroduces
the island fruit flies to the mainland fruit flies,
they will not readily mate with each other due to
differing courtship behaviors. The few that do
mate produce inviable eggs because of genetic
differences in the populations.
• Natural Selection does NOT
produce perfection.
• An organism cannot “adapt”
during its lifetime. It cannot
“try” to change. That is NOT
adaptation. Adaptations
MUST be GENETIC!
• Natural Selection is NOT
random: variations that aid
survival and reproduction
are more likely to become
common in the population
What I
NEED is a
GOOD FUR
COAT!
EVOLUTION
DOES NOT
WORK THIS
WAY!!!
Misconceptions