Download Early Earth and Evolution

Evolution: How species
have changed over time
First a Perspective of Time
18th/19th century thoughts

Focus on variability

Paleontology emerges as a science
study of prehistoric fossils and rocks
 Stratification of rock
 Variation in species (prehistoric and current)

Uniformitarianism
 Catatastrophism

Evolution at its most basic

Change over time

In reality: change in allele frequencies 
change in phenotypes
Those who influenced Darwin
http://www.pbs.org/wgbh/evolution/library/02/5/l_025_01.html
Charles Darwin
a Naturalist – mostly observed
organisms in their natural habitats
rather than conducting experiments.
 Was
 Made
most of his observations on the
Galapagos Islands
Charles Darwin
 Did
much of his work in the Mid1800’s
** Keep in mind this is BEFORE
Mendel, Watson and Crick***
Charles Darwin
 Introduced
the idea of Natural Selection
as a way for new species to form
(speciation).
 Published
The origin of Species in 1859



http://www.youtube.com/watch?v=F_IhC_5FfbE
http://www.youtube.com/watch?v=oMYSMdqzFEA
http://www.youtube.com/watch?v=hJu2gZQRmTM
THE GENIUS OF CHARLES DARWIN
 Note: These videos have great information
about the theory of evolution. But keep in
mind… he is trying to disprove another
theory.

The Theory of Natural Selection
 Assumptions:
 There
are not enough resources for all
to survive
 genetic variation exits in all populations.
Results:
1. Competition
2. Survival of the fittest
3. Descent with modification
Assumption 1: Not enough
resources
 What
resources are we talking about?
Food
 Are
Shelter
Suitable
Mates
there enough for everyone?
Assumption 2: Genetic variation
exists
 Where
do these differences come from?
Mutations Genetic
Recombination
Sexual
reproduction
Migration
 Remember
it doesn’t have to be a NEW
gene, just a new combination of genes
Result 1. Competition
 What
 Who
are we competing over?
 What
wins? What is the prize?
happens to those that don’t win?
Result 2. Survival of the Fittest
 In
nature are we all really equal?
 What
 Is
do we mean by “fittest”?
it enough to survive?
Result 3. Descent with Modification
 Break
it up, what does it mean?
 What
happens to the frequency of fit
genes and unfit genes?
 What
do we see in future generations?
3. Descent with Modification
 New
generations will resemble
previous generations (descent) BUT
more individuals will have the “best”
variation PLUS new mutations and
combinations (with modification)
An Example
Example:
 What
is the genetic variation?
 What is the selective pressure?
 Who has the advantage?
 What would we predict for the next
generation?
 Why might the “unfit” phenotype stick
around?
Types of Selection – some
examples of natural and artificial
 Natural
Selection
What determines which variation gets passed on?
 What is the outcome?

 Artificial
Selection (a.k.a. selective
breeding)
What determines which variation gets passed on?
 What is the outcome?

Types of Selection
Directional Selection: One extreme or the
other is “favored” and increases in
frequency while midrange and other
extreme decrease
Types of Selection
Stabilizing Selection: Midrange is favored
and increases in frequency while both
extremes decrease.
Types of Selection
Diversifying/disruptive Selection: Both
extremes are favored and increase while
midrange decreases.
At what point is a new species
formed?
 Evolution
– change in allele frequency
– such change that new
population is a different species
 Speciation
– two organisms that can successfully
reproduce and produce viable, fertile
offspring
Examples:
Cross between a Pug and a Beagle
- different breeds but SAME species
Examples:
Offspring: Puggle!
Both viable (obviously) and fertile
Examples:
Cross between a Horse and Donkey
- different species
Examples:
Offspring: Mule!
Viable but infertile
Gene Pool Isolation
 Two
populations become separated so
their genes are no longer mixed
 Mutations
appear independently in
each population
 Selection
happens independently in
each population
Mechanisms of Isolation

Geographic – Physical barrier separates two
populations

Behavioral – mating behaviors of some are not
attractive to others.

Temporal – fertility occurs at different times

Mechanical – different physical means of
reproduction
Principle of a Common Ancestor
with Modification – over
generations descendents can look quite
different from ancestors.
 Descent
 Thus,
organisms that seem very different
might share a common ancestor
 Suggests
if you go far enough back, we
are all related!
Phylogenetic tree: Family Tree
of Life
Common ancestor

Humans and chimps have a common ancestor.

THAT IS NOT THE SAME AS SAYING WE
WERE ONCE CHIMPS!!!

Think about it: Do you and your cousin share a
common ancestor? Does that mean you are
your cousin? Does that mean that either of you
are that ancestor?
Evidence of Common ancestry
 Comparative
Anatomy
 Comparative Embryology
 Comparative Biochemistry

See Determining evolutionary relationships
assignment
Rules of Evolution
 Mutations and their phenotypes are
random. Meaning?
 Variation
must exist in the population
BEFORE selective pressure occurs
Rules of Evolution
 Individuals can not evolve, only
species
A
fit trait in one environment might be
eliminated as a weakness in another
Evidence of a Universal
Common Ancestor
 What
do we ALL have in common
Additional Evidence of Evolution
(but not necessarily common ancestry)
Fossil Record
 Preserved
remains of ancient
life in sedimentary
rock
 Even
of species
no longer in
existence (most!)
Fossils
 Fossils
are often
found in the
layers of
sedimentary rock.
 See
changes in
fossils over time
Dating Fossils
Absolute Dating:
 Using radioactive
organic material in
a sample we can
get a more
accurate age of a
fossil

Dating Fossils
Relative Dating:
 Fossils found in
lower levels are
older than upper
levels.


Can’t provide exact
age, just which is
older
Dating Fossils
Absolute Dating:
 Radioactive
organic material is
used to get a more
accurate age of a
specimen.

 Radioactive
material decays into a
non-radioactive decay product at a
steady rate.
 Half
life = time it takes half a sample
to decay.
Example: Some carbon is naturally
radioactive – C14.
Half life of C14 – 5,730 years
Decay product is N14
If we look at the sample and determine
the ratio of C14 to N14 we can get an
idea of how much time has passed
Assume we start with a sample that is
100g of C14
C-14
remaining
C14:N14
Years from
start date
100g
1:0
0
50g
1:1
5,730
25g
1:3
11,460
12.5
1:7
17,190
Geographic Distribution
 Biogeography
and Convergent
Evolution:

See Determining evolutionary relationships
assignment
Vestigial Organs
 Structures
that serve little to no purpose
NOW
 Snake skeletons with leg bones and
pelvis
 Blind, cave-dwelling fish have eyesockets but no eyes.
Vestigial Organs
 Gives
insight into PAST needs of
organism as well as where this
organism has come from
 What
happens first:
Need
Or
for organ disappears?
mutated organ appears?
Evidence in support of evolution

Vestigial structures

See handout
Evidence in support of Evolution

Comparative Biochemistry

See handout
Genetics in Evolution
Darwin did his work before Mendel
and didn’t understand genes or
how inheritance worked.
Thanks to Mendel we know
how/why traits get passed from
parent to offspring
Gene Pool

The set of all genes (and their alleles)
within a population or species.

The set of all genes within interbreeding
populations

The frequency of alleles, and even genes
can change.
Phenotypes NOT genotypes
 Natural
selection acts on phenotypes
NOT genotypes
But in turn will influence allele frequency.
Alleles and allele frequencies determine
the gene pool
Why aren’t all bad alleles eliminated??
Mechanisms of Evolution
 Things
that cause the allele
frequencies to change
 Remember,
it is variation that
proposes and selection that
disposes
Sources of Genetic Variation

Mutations

Crossing over

Independent assortment

Sexual reproduction
External factors impacting allele
frequency

What happens that results in changes in
phenotype (remember selection acts on
phenotypes, which impact genotypes
Genetic Drift (founder’s effect is one type)
 Endosymbiosis
 Mass extinction
 Adaptive radiation

Mechanisms of Evolution
Genetic Drift
 Evolution
without natural selection
 Chance
occurrences change allele
frequency
 More
common in small populations
 What
if more of the “unfit” survive?
Genetic Drift  Founder Effect
Sample of
Original Population
Descendants
Founding Population B
Mechanisms of Evolution
Endosymbiotic theory
• Mitochondria and chloroplasts evolved
from free living prokaryotic organisms
•
A larger cell engulfed them
•
A symbiotic relationship formed
Endosymbiotic theory
Evidence of endosymbiosis
 Both
have their own DNA and produce
their own proteins
 Both
reproduce independently from the
cell through a process like binary fission
(bacterial reproduction)
 Double
membranes of both are similar to
prokaryotic membranes
Patterns of Evolution
 Mass
Extinction
 Periodic
large-scale extinction
events
 Dramatically changes landscape
eliminating or creating selective
pressures
Patterns of Evolution
 Adaptive
Radiation
Single species evolves into
several different species that
live in different ways
(adaptations)
Patterns of Evolution
 Co-evolution
 Due
to close
relationship two
species share with
each other, change
in one organism
results in a change
with the other.
Patterns of Evolution
 Gradualism
 What
Darwin subscribed to
 Tiny changes accumulate over
huge period of time to yield large
changes.
Think
Grand Canyon only organisms
Patterns of Evolution
 Punctuated
Equilibrium
 More
modern theory proposed by Gould
and Eldridge
 Proposed
change occurs in spurts
followed by periods of stasis
 More
support in fossils!
Are organisms always evolving?

Hardy Weinberg Equilibrium – suggests no!

Under certain conditions, populations won’t
evolve
Conditions:
1. Large population
2. No migration in or out
3. No natural selection
4. Random Mating
5. No net mutations

How do we tell?
Determine allele frequencies over different
generations and see if they change
 p = frequency of dominant allele
 q = frequency of recessive allele



p+q=1
p2 + 2pq + q2 = 1
p2 = frequency of homozygous dominant
q2 = frequency of recessive genotype
2pq = frequency of heterozygote
Example problem:

A population of aphids can either be brown or
green. Green is recessive. In a population of
1000 aphids 250 are green. What are the
allele frequencies for the green and brown
alleles?

Then figure out the homozygous dominant and
heterozygote populations too.