Download Lecture: Processes of Evolution

PROCESSES OF EVOLUTION
1. What are species?
2. What are the processes of evolution?
3. How do these processes interact to
bring about evolution as we understand
it today?
1. SPECIES
•
Population of organisms whose members can, under
natural circumstances, freely interbreed with one
another and produce fertile offspring
Examples:
Dogs & Wolves = can (but often do not) produce fertile
offspring, so now in same species canis lupus
Horses & Donkeys = produce mules, but infertile
Lions & Tigers = can produce fertile offspring, but never in
the wild! (different behavioral niches)
Why is Distinction among Various
Species so Vague?
•
Species emerge OVER TIME!
•
All species evolve at different rates!
•
Humans are making up the
rules/categories!
2. WHAT ARE THE PROCESSES OF
EVOLUTION?
EVOLUTION = changes in allele
frequency through time
1.
2.
3.
4.
MUTATION
NATURAL SELECTION
GENE FLOW
GENETIC DRIFT
Allele = variants of a gene, carry different
instructions for development of a phenotype
Mutations
might happen!!
Sex cells
Crossing Over
Recombination
Body cells
1. MUTATION
•
Any change in the genetic code
•
Bioanthropologists are interested in
mutations in the sex cells (gametes)
•
Changes allele frequency
•
Adds GENETIC VARIATION to a species
gene pool
Trisomy 21 =
Example of Mutation
•
Chromosomal
mutations =
mutations of whole
or large portion of
chromosome
•
3 copies of
chromosome 21=
Trisomy 21 or Down
syndrome
•
During MEIOSIS, a
pair of chromosomes
did not segregate
2. NATURAL SELECTION
•
Definition = Evolutionary change based
on the differential reproductive success of
individuals within a species
•
When is an individual successful?
When s/he has a phenotype (trait) that is
important for the adaptation of a
particular species to a PARTICULAR
ENVIRONMENT at a PARTICULAR TIME
Darwin’s Finches:
Example of Natural Selection
Beaks and Body Size
(Rosemary and Peter Grant’s research)
•
1977: Year-long, severe drought on a
small Galapagos Island
•
Insects disappear, only tough seeds
left
•
1978: 14% of finches made it
•
Survivors: 5-6% larger than those who
died, longer & deeper beaks
Would the increased body & beak
size be passed on to offspring?
•
Next generation: yes! Larger body
and beak size
•
Several generations later
(environmental conditions back to
normal): beak and body size
decreased toward previous
dimensions
What do we learn?
•
The useful variation (large beaks & bodies)
was ALREADY present! (not “acquired”)
•
Adaptation to change is LUCK! (90% of
Earth’s species are extinct!)
•
NS does NOT produce change in a
particular direction & does NOT ensure
survival of a species!
•
This idea can be uncomfortable! What if
life is unpredictable?
3. GENE FLOW
Definition:
Genes within a species “flow” among the
populations of that species, changing allele
frequencies & adding genetic variation to
the whole species
How does this happen?
Members of different DEMES interbreed &
new genetic combinations may show up in
offspring
Demes:
Breeding populations separated by
environment
Immigration & Sex:
Example of Gene Flow
•
•
•
Today, more
people are
mobile
We find mates
from different
parts of the
world
We add
variation to
human gene
pool!
4. GENETIC DRIFT
Definition:
Genes within a species “drift” when a
population within a species splits. Each new
population exhibits a NONREPRESENTATIVE
sample of the genes of the original
Fission: Splitting of a population
Founder Effect:
When one of the new populations is drawn
from a small sample of the original
population, it will be DIFFERENT genetically
Bottleneck:
Example of Founder Effect
North American Hutterites:
Example of Genetic Drift
•
300 original Hutterites founded
colonies in 1874 & 1875
•
90 people contributed genes to
future generations
•
Today, about 35,000 Hutterites can
trace genes back to less than 100
ancestors!
Sickle Cell Anemia:
Evolutionary Processes In Action
Group Exercise:
Sickle Cell Anemia
1. How did Sickle Cell Anemia come about?
2. What happens when someone is
homozygous (SS) for the Sickling Trait?
3. What does it mean that heterozygotes
(AS) have an adaptive advantage in
malarial areas?
4. How is the connection between sickle cell
and African Americans an example of the
founder effect?
Group Exercise:
Sickle Cell Anemia
5. How can people of European
American ancestry have sickle cell?
6. How is the story of sickle cell an
example of the holistic perspective
of anthropology?