Evolution
Origin of Life and
Speciation
Explain how the giraffe could
have evolved:
What is Natural Selection?
Who came up with the theory of natural
selection?
 Name some criteria necessary for
natural selection to occur.

Name types of evidence for
evolution.
Name types of evidence for
evolution.
Fossil record
 Homologous structures
 Vestigial structures
 Embryonic structures
 Molecular record

What do we mean by survival of
the fittest? Give some examples.
Origin of Life
We have said that all organisms have
ancestors, but not all organisms have
descendants. What do we mean by that?
 What about the first organism? How do
you think life first began on Earth?

Origin of Life

What do you think the first organism was
like?
Early Earth

Early Earth was formed about 4.6 billion
years ago and was very different than
earth today.

How do you think it might have been
different?
Early Earth
The atmosphere was very different than it
is now, containing little or no oxygen.
 Earth was too hot for liquid water.
 Once the surface cooled enough for rocks
to form, the surface was covered with
volcanic activity.

Early Earth
About 3.8 billion years ago the Earth cooled
enough for liquid water to remain.
 Thunderstorms drenched the planet and
oceans covered most of the surface.

Could organic molecules have
evolved under these conditions?

In the 1950’s Stanley Miller and Harold
Urey tried to simulate the conditions of
early Earth.

They showed how several amino acids
could be created under those
conditions.
Miller and Urey’s Experiment

They passed sparks (representing
lightening) through a mixture of hydrogen,
methane, ammonia, and water
(representing the atmosphere)
The Big Picture
 Miller
and Urey showed that the
mixtures of organic
compounds necessary for life
could have arisen on primitive
earth!
Hypothesis of the Origin of Life


The leap from a mixture of organic molecules to
a living cell is large.
Tiny bubbles of organic molecules (called
proteinoid spheres) have characteristics of living
systems such as selectively permeable
membranes and means of storing and releasing
energy. They may have become more and
more like living cells over time.
Hypothesis of the Origin of Life

Experiments have shown that under the
conditions of early Earth, small RNA
sequences could have formed and
replicated on their own. This could have
created a simple RNA-based form of life
from which the DNA system could have
evolved.
Hypothesis of Origin of Life

How certain do you think this
hypothesis is? Do you think it will ever
be changed? Do you think it will be
changed during your lifetime?
Origin of Life

Evidence indicates that about 200-300
million years after the accumulation of
liquid water on Earth, cells similar to
modern bacteria were common.
Changing Earth

Photosynthetic bacteria became common
and oxygen began to accumulate in the
atmosphere and the ozone layer formed.

The rise in oxygen caused some life forms
to go extinct, while others evolved ways to
use oxygen for respiration.
Hypothesis of Origin of Eukaryotic
Cells-Endosymbiotic Theory
What is a eukaryotic cell?
 Prokaryotic cells began to evolve internal
cell membranes- this was the ancestor to
eukaryotic cells.
 Smaller prokaryotes began living inside
this ancestor and over time it became an
interdependent relationship. What does
this mean?

Lynn Margulis’ Endosymbiotic
Theory
One group which entered the cell had the
ability to use oxygen to generate ATP.
These evolved into mitochondria.
 Another group of prokaryotes which
carried out photosynthesis evolved into
chloroplasts.

Evidence for Endosymbiotic Theory
Mitochondria and chloroplasts have many
characteristics of free living bacteria:
1- contain DNA similar to bacterial DNA
2- have ribosomes of similar size and
structure to those of bacteria
3- reproduce by binary fission like bacteria

Any Questions?
Speciation

Speciation: the formation of new species

What is a species?

As new species evolve, the populations become
reproductively isolated from each other. (cannot
interbreed and produce fertile offspring)
How could speciation occur?
Isolating Mechanisms:
Behavioral Isolation: differences in
courtship or reproductive strategies that
prevent breeding
 Geographic Isolation: populations
separated by physical barriers
 Temporal Isolation: reproduce at different
times

Geographic
Isolation
Patterns of Evolution

Adaptive Radiation: when a
species evolves into
several different forms
that live in different ways

Can you think of an
example we have
discussed, or any other
example, of adaptive
radiation?
Patterns of Evolution

Example of adaptive radiation: Darwin’s
finches-more than a dozen species
evolved from a single species
Patterns of Evolution
Convergent Evolution: unrelated
organisms come to resemble one another
due to similar selective pressures
 Example?
 What is divergent evolution?

Divergent Evolution


occurs when two or more biological
characteristics have a common evolutionary
origin but have diverged over evolutionary time.
This is also known as adaptation or adaptive
evolution.
example, the vertebrate limb is one example of
divergent evolution. The limb in many different
species has a common origin, but has diverged
somewhat in overall structure and function.

Structures that are similar due to evolutionary origin, such as the
forearm bones of humans, birds, porpoises, and elephants, are
called homologous. Structures that evolve separately to perform a
similar function are analogous. The wings of birds, bats, and
insects, for example, have different embryological origins but are all
designed for flight.
Patterns of Evolution
Coevolution: when two species evolve
together, in response to changes in each
other
 Can you think of an example?

Coevolution

Example: flowers and pollinators, flowers
and plant-eating insects
Gradual versus Punctuated
Evolution
Gradual: slow and steady change
Punctuated: long, stabile periods
interrupted by brief periods of rapid
change
Any Questions?
Can we see evolution occur?

Can you think of an example of an
organism that evolves “quickly”? One
that has evolved during your life time?
Bacterial Evolution
What allows bacteria to evolve so quickly?
Insect Evolution
Population Genetics

The study of traits and changes in
populations.
Gene Pool
All mechanisms of evolution involve
changes in the gene pool.
 A gene pool is the combined genetic
material of all the members of a given
population.

Microevolution
The change in a population’s alleles over a
period of time.
 These changes manifest themselves in the
organism’s phenotype.
 Since individuals do not evolve, a
population must be watched to detect any
change in genetic modification.

Allelic Frequencies
The number of each allele is a fraction of
all the genes for a particular trait.
 These fractions are known as allelic
frequencies.
 The constant state of allele frequencies is
called genetic equilibrium.

Hardy-Weinberg Principle
Developed to determine if a population is
evolving.
 Authors of the theorem set up parameters,
which do not exist in nature, to be followed
when determining the allele frequencies of
any population…

Hardy Weinberg conditions
The population must be very large in size.
 It must be isolated from other populations
(no gene flow)
 No mutations
 Random mating
 No natural selection

Mathematical Wedding of Mendel
and Darwin: The Hardy Weinberg
Theorem


p+q = 1
p2 + 2pq + q2 = 1
p
represents the frequency of the dominant allele
 q represents the frequency of the recessive allele
 p2 represents the frequency of the homozygous
dominant phenotype
 2pq represents the frequency of the heterozygous
phenotype
 q2 represents the frequency of the homozygous
recessive phenotype
Hardy Weinberg Problems
Causes for
Microevolution
1.
Genetic Drift : The random change
in gene pools due to random events.
•
Examples: migrations, natural
disasters, isolation
•
Bottleneck effect: genetic drift
occurring after a random population
reducing event
•
Founder’s effect: the effect of
establishing a new population by a
small number of individuals, carrying
only a small fraction of the original
population's genetic variation.
•
As a result, the new population
may be distinctively different,
both genetically and
phenotypically, from the parent
population from which it is
derived.
•
In extreme cases, the founder
effect is thought to lead to the
speciation and subsequent
evolution of new species.
Genetic Drift and the Founder
 Polydactyly -- extra fingers
Effect
or sometimes toes -- is one


symptom of Ellis-van
Creveld syndrome.
The syndrome is commonly
found among the Old Order
Amish of Pennsylvania, a
population that experiences
the "founder effect."
Genetically inherited
diseases like Ellis-van
Creveld are more
concentrated among the
Amish because they marry
within their own
community, which prevents
new genetic variation from
entering the population.
Causes for Microevolution
2.
Gene Flow

The movement of alleles into and out of a
population
 Migration of an organism into different areas
can cause allelic frequency changes


Immigration
Emigration
Causes for Microevolution
3.
Mutations

These change the genome of an organism
and are an important source of natural
selection
Causes for Microevolution
Nonrandom Mating
Natural Selection
4.
5.
•
Those individuals
who leave behind
more offspring, pass
on more of their
alleles and have a
better success rate
in dominating the
population.
Normal Distribution


Most common in
nature
Bell-shaped curve
Directional Selection

A change in the
environment favors
an extreme
phenotype
Examples of
Directional Selection


Evolution in horse limb
morphology illustrates
directional selection-over time, natural selection
favored individuals with
limbs adapted for
running on open grassland
areas.
Yet another soon-to-beclassic example of
directional selection at work:
antibiotic resistance in
bacteria.
Disruptive Selection


An environmental change
makes it unfavorable to have
the medium phenotype
Batesian mimicry gives an
example of disruptive
selection. Some places in
Africa have three species of
bad tasting butterflies.
Different females of edible
swallowtail butterflies mimic
each of the distasteful species.
Class Activity: Fishy Frequencies
(or How Selection Affects the
Hardy-Weinberg Equilibrium)

Introduction:
 Understanding
natural selection can be confusing and
difficult. People often think that animals consciously
adapt to their environments - that the peppered moth
can change its color, the giraffe can permanently
stretch its neck, the polar bear can turn itself white - all
so that they can better survive in their environments.
 In this lab you will use fish crackers to help further your
understanding of natural selection and the role of
genetics and gene frequencies in evolution.
Background: Facts about the
'Fish'





These little fish are the natural prey of the terrible fish-eating sharks YOU!
Fish come with two phenotypes of gold and brown:
 gold: this is a recessive trait (f); these fish taste yummy and are easy
to catch.
 brown: this is a dominant trait (F); these fish taste salty, are sneaky
and hard to catch.
You, the terrible fish-eating sharks, much prefer to eat the yummy gold
fish; you eat ONLY gold fish unless none are available in which case
you resort to eating brown fish in order to stay alive.
New fish are born every 'year'; the birth rate equals the death rate. You
simulate births by reaching into the container of 'spare fish' and selecting
randomly.
Since the gold trait is recessive, the gold fish are homozygous recessive
(ff). Because the brown trait is dominant, the brown fish are either
homozygous or heterozygous dominant (FF or Ff).
Hardy-Weinberg:




For fish crackers, you assume that in the total population, you have
the following genotypes, FF, Ff, and ff. You also assume that mating
is random so that ff could mate with ff, Ff, or FF; or Ff could mate
with ff, Ff, or FF, etc. In addition, you assume that for the gold and
brown traits there are only two alleles in the population - F and f. If
you counted all the alleles for these traits, the fraction of 'f' alleles
plus the fraction of 'F' alleles would add up to 1.
The Hardy-Weinberg equation states that: p2 + 2pq + q2 = 1
This means that the fraction of pp (or FF) individuals plus the fraction
of pq (or Ff) individuals plus the fraction of qq (ff) individuals equals
1. The pq is multiplied by 2 because there are two ways to get that
combination. You can get F from the male and f from the female OR
f from the male and F from female.
If you know that you have 16% recessive fish (ff), then your qq or q2
value is .16 and q = the square root of .16 or .4; thus the frequency
of your f allele is .4 and since the sum of the f and F alleles must be
1, the frequency of your F allele must be .6 Using Hardy Weinberg,
you can assume that in your population you have .36 FF (.6 x .6) and
.48 Ff (2 x .4 x .6) as well as the original .16 ff that you counted.