Chapter 15-17
Evolution
What is evolution?
Evolution is change over time
 Theory of evolution – process by which
modern organisms have descended from
ancient organisms
 Remember that a scientific theory is a wellsupported testable explanation of phenomena
that have occurred in the natural world

Where did the idea of evolution
come from?

Charles Darwin made numerous observations
and collected evidence that led him to propose
his hypothesis about the way life changes over
time
◦ Collected plant/animal specimens where ship
anchored
◦ Learned that an enormous number of species
exist
◦ Noticed how well suited organisms are to
their environment
Galapagos Tortoises
Lamarck and Evolution

In 1809 Lamarck proposed that by selective use
or disuse of organs, organisms acquire or lose
certain traits
◦ These traits can then be passed to offspring
◦ This could lead to a change in the species
Lamarck and Evolution
Darwin and Evolution

“On the Origin of Species” was published in 1859
by Charles Darwin
◦ Darwin proposed natural selection as a
mechanism for evolution
◦ Competition for resources leads to survival of
the fittest
◦ Successful adaptation means the organism has
and advantage to survival and reproduction
◦ Adaptation – any inherited characteristic that
increases an organism’s chance of survival
◦ Over time natural selection results in the
inherited characteristics of a population
Darwin and Evolution
Darwin proposed that each species has
descended, with changes, from other species
over time (descent with modification)
 The principle of common descent states that all
species (living and extinct) were derived from
common ancestors (single “tree of life”)
 Darwin hypothesized that living things have
been evolving for millions of years
◦ Evidence found in fossil record, geographical
distribution of species, homologous structures
of organisms, similarities in early development

Darwin and Evolution
Types of Evolution
Micro-evolution – change in a population’s gene
frequencies
 Macro-evolution – when a new species emerges

Species – group of organisms that can
reproduce with fertile offspring in nature
 Variation in the population provides the
material for natural selection. Sexual
reproduction (the shuffling of alleles and, thus,
uniqueness) provides for this variation

Evidence for Evolution



The fossil record - Strata of fossilized remains of
organisms extinct for many years. The oldest layers
have the oldest fossils beginning with bacteria.
Biogeography – the presence of organisms in areas
of the world correlates with the movement of land
masses over time
◦ Australia has a unique abundance of marsupials
found no where else in the world
Comparative anatomy – Organisms share many
characteristics called homologous structures
◦ Vestigial structures are parts reduced in size or
no longer used by a more recent organism, ex.
hip bones of whales
Geographic Distribution of Species
Homologous Body Structures
Evidence for Evolution



Comparative embryology – Similarities exist
between many animals as they are developing
DNA or molecular similarities – All organisms
share the same genetic code, ATCG’s. Most of the
codons match the same amino acids.
Population studies – We can see bacterial
populations change over time
◦ Bacteria exposed to antibiotics will die except for
the resistant few
◦ The resistant ones live and reproduce, creating a
population of bacteria resistant to the antibiotic.
Similarities in Embryology
Evolution and Isolation
Geographic isolation – when populations are
split by geographic barriers, they sometimes
change so that when brought back together,
they can’t have offspring together
 Reproductive isolation – when organisms in a
population do not interbreed for some reason
and become distinctly different groups.
◦ In plants this can occur as a mistake in
meiosis, and the new plant will not have the
correct chromosome number for successful
zygote formation. ex. salamander ring species

Genetics and Evolution
Gene pool- all genes, including the different
alleles, in a population
 Relative frequency- number of times that an
allele occurs in a gene pool
 Genetically, evolution is any change in the
relative frequency of alleles in a population
◦ Mouse fur frequencies begin B is 40%, b is
60%
(B=black, b=brown)
◦ If it changes to B=30%, then the population is
evolving

Sources of Genetic Variation
Mutations are a change to the sequence of
DNA, which may result in a phenotype change
◦ Can be caused by mistake in replication or
radiation/chemicals
 During gamete productions gene shuffling
occurs (independent assortment and crossing
over)
◦ Can produce a huge variety in phenotypes
◦ Does not change relative frequency
◦ Can result in unique phenotypes that could be
an advantage

Genetics and Evolution
Evolutionary fitness is an organism’s success at
passing genes to the next generation
 However, natural selection never acts on genes
only on the organism as a whole
 In addition, evolution is about the frequency of
alleles for an entire population, not and
individual organism

Genetics and Evolution
Natural selection on single-gene traits can lead
to changes in allele frequencies and thus to
evolution
 The red lizards are more visible; black lizards
warm faster, which allows them to be more
active sooner

Genetics and Evolution

Natural selection can affect polygenic traits
(trait controlled by 2 or more genes) in 3 ways:
◦ Directional selection occurs when individuals
on one end of a phenotype curve have higher
fitness
Low mortality,
high fitness
High mortality,
low fitness
Genetics and Evolution
◦ Stabilizing selection occurs when higher
fitness at the center of the curve than the
ends
Low mortality,
◦ Weight of
Selection
high fitness
against both
High mortality,
extremes keep
human infants
low fitness
Brightness of
Feather Color
curve narrow
and in same
place.
Genetics and Evolution
◦ Disruptive selection occurs when the ends of
the phenotype curve have higher fitness than
the middle
 Can cause it to split into 2
 Medium sized seeds become less common
Genetics and Evolution

Genetic equilibrium occurs when allele
frequencies remain constant; 5 requirements
◦ Random mating (not true in organisms like
elk)
◦ Large population
◦ No movement into or out of the population
◦ No mutations
◦ No natural selection
History of Life
Biogenesis – Life comes only from life.
 Abiogenesis – spontaneous generation, life can
come from the nonliving

Louis Pasteur – disproved spontaneous
generation by sterilizing broth solutions.
 Stanley Miller and Harold Urey (1950’s)
simulated early earth in the lab. By making
amino acids in the lab.
http://www.ucsd.tv/miller-urey/

Pasteur’s Experiment
Miller and Urey Experiment