Chapters 16 and 17:
Evolution – part II
Evidence for evolution
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Fossils
Biogeography
Developmental biology
Anatomy
• Homologous structures
• Analogous structures
• Vestigial organs
• Biochemistry
•Fossil Evidence
•Fossils – traces of organisms that lived in the past
•Ex: shells, bones, teeth, imprints
•Tell us things such as age, habitat, diet, &
lifestyle of organisms.
•Record is incomplete – many organisms leave
no fossils behind
•Most found embedded in sedimentary rock
•Usually, any given layer is older than the one
above it, and younger than those below.
•Biogeography - the study of the locations
of organisms around the world
•Darwin saw similarities of organisms on
different continents but similar
environments
•Differences in organisms due to
geographic separation
•Continental drift can explain how some of
this may have occurred – distribution of
plants and animals is consistent with this
Emu (Australia)
Ostrich (Africa)
Rhea (South America)
Similar animals from different continents
Continental drift
•Developmental biology – the more similar the
embryos are at certain stages of development,
the more closely related they are thought to be.
Significance of developmental
similarities
Human embryo at 5-6 weeks of development
Anatomical Evidence
• All vertebrate forelimbs contain the same sets of
bones – this strongly suggests common they
evolved from a common ancestor.
• Homologous structures – characteristics that are
similar in two or more species and that have been
inherited from a common ancestor of those species
• Ex: frog, lizard, bird, whale, cat, bat, and
human forelimbs
Bones of vertebrate forelimbs
• Analogous structures - used for the same
purpose but are not due to a common
ancestor
• Ex: bird wing & insect wing
• Vestigial structures – structures that have no
function in the living organism but may have
been used by its ancestors.
• Ex: human appendix,
python leg bones
• Biochemistry – comparisons of DNA or amino
acid sequences in proteins
• The more similar the genes and proteins are, the
more closely related organisms are thought to be
• Ex: Hemoglobin to carry oxygen is identical in
humans and chimpanzees.
• All use DNA, ATP, and many identical or
nearly identical enzymes.
• Organisms use the same triplet code and the
same 20 amino acids in proteins.
• Universal genetic code is evidence for
evolution
Significance of biochemical
differences
Population genetics
•Gene pool – total of all the genes of all the
individuals in a population
•If the frequency of genes in a population
changes, evolution has occurred
•Gene frequencies will change to confer
survival and reproductive success
Microevolution vs. macroevolution
•Microevolution – refers to evolution as a
change in genes within populations
•Macroevolution – refers to the appearance of
new species over time
•Speciation – the formation of a new species
•Species – a group of organisms that are
closely related and that can mate and produce
fertile offspring
•New species appear when reproductive
isolation occurs
Example of microevolution
•Speciation occurs when one population
is isolated from another population
•Isolation can be geological,
reproductive, or filling different
ecological niches to reduce
competition
•With isolation comes changing
environmental factors exerting
selective pressure on mutations and
adaptations.
• Reproductive isolation: a state in which a
population can no longer interbreed with
other populations to produce future
generations
• Reproductive isolation can occur due to:
– Pre-mating isolating mechanism reproduction is not attempted
– Post-mating isolating mechanisms - do
not produce fertile offspring
• Hybrids - Offspring produced by the
interbreeding between two different
species
• Examples of hybrids:
1. Zebra x horse
2. M. lion & F. tiger
3. F. lion & M. tiger
4. Killer whale & dolphin
5. M. donkey & F. horse
6. F. donkey & M. horse
7. Zebra x donkey
8. Camel x llama
9. Buffalo x cow
10.Sheep x goat
11.Lemon x lime
12.Tangerine x lemon
13.Broccoli x cauliflower
14.Tangerine x grapefruit
15.Grape x apple
Processes of microevolution:
•Natural selection – some are better suited to
survive and reproduce than others
•Migration – movement of individuals into,
out of, or between populations
http://nortonbooks.com/college/biology/animations/ch17a01.htm
•Mate choice – mates are limited, or selecting
a mate based on appearance or behavior
•Mutation – changes genes within population
•Genetic drift – random events cause only
certain individuals to survive and reproduce
genetic drift animation
•Examples of genetic drift:
•Founder effect - Founding member of Amish
population had recessive allele for rare kind of
dwarfism - % of Amish with this allele higher
than in general population
•Random death of certain color animals results
in only one color reproducing next generation
Patterns of macroevolution:
•Convergent evolution
•Coevolution
•Adaptive radiation
•Extinction – if all members of a species
die off or fail to reproduce, the species
is said to be extinct
•Gradualism
•Punctuated equilibrium
•Convergent evolution – species living in
similar environments should evolve similar
adaptations
•Coevolution – change of two or more
species in close association with each other
•Ex: predator & prey, parasite & host,
insects and plants they pollinate
Other examples
• Adaptive radiation - an evolutionary
pattern in which many species evolve
from a single ancestral species
• Tends to happen when a new species
enters an environment that contains
few other species
– Ex: several species of finches on the
Galapagos Islands - each one has a
different way of life.
The Galapagos finches
• Gradualism – suggests that change is
slow and steady; large-scale changes
require many small-scale changes over
a period of time.
• Punctuated equilibrium – suggests that
a period of no change is interrupted by
period of rapid change; species is
stable, then environmental changes
create new pressures, causing new
species to suddenly appear
Gradualism versus punctuated
equilibrium