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Evolution: How species have changed over time. First a Perspective of Time. Those who influenced Darwin. Charles Darwin. Was a Naturalist – mostly observed organisms in their natural habitats rather than conducting experiments. Made most of his observations on the Galapagos Islands.

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charles darwin
Charles Darwin
  • Was a Naturalist – mostly observed organisms in their natural habitats rather than conducting experiments.
  • Made most of his observations on the Galapagos Islands
charles darwin1
Charles Darwin
  • Did much of his work in the Mid-1800’s

** Keep in mind this is BEFORE Mendel, Watson and Crick***

charles darwin2
Charles Darwin
  • Introduced the idea of Natural Selection as a way for new species to form (speciation).
  • Published The origin of Species in 1859
the theory of natural selection
The Theory of Natural Selection
  • Assumptions:
    • There are not enough resources for all to survive
    • genetic variation exits in all populations.


  • Competition
  • Survival of the fittest
  • Descent with modification
assumption 1 not enough resources
Assumption 1: Not enough resources
  • What resources are we talking about?

Suitable Mates



  • Are there enough for everyone?
assumption 2 genetic variation exists
Assumption 2: Genetic variation exists
  • Where do these differences come from?

Sexual reproduction

Genetic Recombination



  • Remember it doesn’t have to be a NEW gene, just a new combination of genes
result 1 competition
Result 1. Competition
  • What are we competing over?
  • Who wins? What is the prize?
  • What happens to those that don’t win?
result 2 survival of the fittest
Result 2. Survival of the Fittest
  • In nature are we all really equal?
  • What do we mean by “fittest”?
  • Is it enough to survive?
result 3 descent with modification
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
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)

  • 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?
rules of evolution
Rules of Evolution
  • Mutations and their phenotypes are random. Meaning?
  • Variation must exist in the population BEFORE selective pressure occurs
rules of evolution1
Rules of Evolution
  • Individuals can not evolve, only species
  • A fit trait in one environment might be eliminated as a weakness in another
types of selection
Types of Selection
  • 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 selection1
Types of Selection

Directional Selection: One extreme or the other is “favored” and increases in frequency while midrange and other extreme decrease

types of selection2
Types of Selection

Stabilizing Selection: Midrange is favored and increases in frequency while both extremes decrease.

types of selection3
Types of Selection

Diversifying/disruptive Selection: Both extremes are favored and increase while midrange decreases.

at what point is a new species formed
At what point is a new species formed?
  • Evolution – change in allele frequency
  • Speciation – such change that new population is a different species

– two organisms that can successfully reproduce and produce viable, fertile offspring


Cross between a Pug and a Beagle

- different breeds but SAME species


Offspring: Puggle!

Both viable (obviously) and fertile


Cross between a Horse and Donkey

- different species


Offspring: Mule!

Viable but infertile

gene pool isolation
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
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
Principle of a Common Ancestor
  • Descent with Modification – over generations descendents can look quite different from ancestors.
  • Thus, organisms that seem very different might share a common ancestor
  • Suggests if you go far enough back, we are all related!
common ancestor
Common ancestor
  • Humans and chimps have a common ancestor.
  • 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
Evidence of Common ancestry
  • Comparative Anatomy
  • Comparative Embryology
  • Comparative Biochemistry
    • See Determining evolutionary relationships assignment
evidence of a universal common ancestor
Evidence of a Universal Common Ancestor
  • What do we ALL have in common
additional evidence of evolution but not necessarily common ancestry
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 are often found in the layers of sedimentary rock.
  • See changes in fossils over time
dating fossils
Dating Fossils
  • Absolute Dating:
  • Using radioactive organic material in a sample we can get a more accurate age of a fossil
dating fossils1
Dating Fossils
  • Relative Dating:
  • Fossils found in lower levels are older than upper levels.
  • Can’t provide exact age, just which is older
dating fossils2
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

geographic distribution
Geographic Distribution
  • Biogeography and Convergent Evolution:
    • See Determining evolutionary relationships assignment
vestigial organs
Vestigial Organs
  • Structures that serve little to no purpose NOW
    • Snake skeletons with leg bones and pelvis
    • Blind, cave-dwelling fish have eye-sockets but no eyes.
vestigial organs1
Vestigial Organs
  • Gives insight into PAST needs of organism as well as where this organism has come from
  • What happens first:
    • Need for organ disappears?
    • Or mutated organ appears?
genetics in evolution
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

phenotypes not genotypes
Phenotypes NOT genotypes
  • Natural selection acts on phenotypes NOT genotypes

But in turn will influence allele frequency.

Why aren’t all bad alleles eliminated??

mechanisms of evolution
Mechanisms of Evolution
  • Remember, it is variation that proposes and selection that disposes
mechanisms of evolution1
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
Genetic Drift  Founder Effect

Sample of

Original Population


Founding Population B

mechanisms of evolution2
Mechanisms of Evolution
  • Endosymbiotic theory
  • Mitochondria and chloroplasts evolved from free living prokaryotic organisms
  • A larger cell engulfed them
  • A symbiotic relationship formed
evidence of endosymbiosis
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
Patterns of Evolution
  • Mass Extinction
    • Periodic large-scale extinction events
    • Dramatically changes landscape eliminating or creating selective pressures
patterns of evolution1
Patterns of Evolution
  • Adaptive Radiation
    • Single species evolves into several different species that live in different ways (adaptations)
patterns of evolution2
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 evolution3
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 evolution4
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
Are organisms always evolving?
  • Hardy Weinberg Equilibrium – suggests no!
  • Under certain conditions, populations won’t evolve
    • Conditions:
    • Large population
    • No migration in or out
    • No natural selection
    • Random Mating
    • No net mutations
how do we tell
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
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.