Evolution
The Nature of Change
and Variation
What is Evolution?
Simply…
a change in living
organisms over time
Why study evolution?
Evolutionary concepts provide a solid
foundation to much of modern
biology

-
you can’t fully understand current trends in biology
or you will have difficulty understanding evolution
Why Study Evolution?

Evolution
involves inheritable changes in organisms
through time
 is fundamental to biology and paleontology
 Paleontology is the study of life history as
revealed by fossils


Evolution is a unifying theory
like plate tectonic theory
that explains an otherwise encyclopedic collection of
facts



Evolution provides a framework

for discussion of life history
Misconceptions about Evolution

Many people have a poor understanding
of the theory of evolution
 they hold a number of misconceptions,
 which include:

evolution proceeds or advances strictly by chance
 nothing less than fully developed structures

– such as eyes are of any use

there are no transitional fossils
– so-called missing links
– connecting ancestors and descendants

humans evolved from monkeys
– so monkeys should no longer exist
What is a scientific “theory”?
Evolutionary theory is the framework
tying together all of biology.
It explains similarities and differences between
organisms, fossils, biogeography, drug resistance,
relative virulence of parasites, and much more.
Theories are structures of ideas that explain and
interpret facts.
In the early days...

Prior to 1760 -people believed organisms
were fixed- that is they didn’t change

1744-1829 – Jean Baptiste Lamarck
Evolution through the inheritance of
acquired characteristics
 Traits acquired during an organism’s life
could be passed on to their offspring
 Giraffes long necks explained by repeated
stretching
 hypothesis rejected

Lamarck’s Giraffes

According to Lamarck’s theory of
inheritance of acquired characteristics
– ancestral
–
–
–
–
short-necked
giraffes
stretched their
necks
to reach leaves
high on trees.
Their
offspring were
born
with longer
necks
Lamarck’s Theory

Lamark’s theory was not totally disproved
until decades later
 with the discovery that genes cannot be
altered by any effort by an organism during its
lifetime

Basic Types of Evolution

Macroevolution = speciation – the
formation of new species. The change
in species over long periods of time.
Not immediately observable.
Microevolution = changes in
genes/alleles within a population.
 Can be observed in a human lifetime.

Macroevolution/Microevolution
Macroevolution
Microevolution
1. Large-scale changes
in gene frequencies
2. Occurs over a longer
(geological) time
period
3. Occurs at or above
the level of species in
separated gene pools
4. Consists of extended
microevolution
1. Small-scale changes
in gene frequencies
2. Occurs over a few
generations
3. Occurs within a
species or population
in same gene pool
4. Refers to smaller
evolutionary changes
Macroevolution/Microevolution
Macroevolution
5. Has not been
directly observed
6. Evidence based on
remnants of the past
7. More controversial
8. Example: Birds from
reptiles
Microevolution
5. Observable
6. Evidence produced
by experimentation
7. Less controversial
8. Example: Bacterial
resistance to
antibiotics
Biological Evidence
Supporting Evolution
If all existing organisms descended with
modification from ancestors that lived
during the past,
 all life forms should have fundamental
similarities:

all living things consist mainly of carbon,
nitrogen hydrogen and oxygen
 their chromosomes consist of DNA
 all cells synthesize proteins


in essentially the same way
Evolutionary Relationships
Biochemistry provides evidence for evolutionary
relationships
 Blood proteins are similar among all mammals
 Humans’ blood chemistry is related

most closely to the great apes
 then to Old World monkeys
 then New World monkeys
 then lower primates such as lemurs


Biochemical test support the idea
 that birds descended from reptiles
 a conclusion supported by evidence in the
fossil record
Natural Selection—Main Points

Organisms in all populations
possess heritable variations such as
 size, speed, agility, visual acuity,
 digestive enzymes, color, and so forth


Some variations are more favorable than others
some have a competitive edge
 in acquiring resources and/or avoiding predators


Not all young survive to reproductive maturity
Those with favorable variations
 are more likely to survive
 and pass on their favorable variations

“Survival of the Fittest”

In common nonscientific usage,
natural selection is sometimes expressed as
 “survival of the fittest”

This is misleading because natural selection is
not simply a matter of survival
- but involves differential rates
of survival and reproduction
Not only Biggest, Strongest, Fastest

One misconception about natural selection
is that among animals
 only the biggest, strongest, and fastest
 are likely to survive
 These characteristics might provide an advantage
 but natural selection may favor
 the smallest if resources are limited
 the most easily concealed
 those that adapt most readily to a new food source
 those having the ability to detoxify some substance
 and so on...
Darwin observed Galapagos finches
showing variations in beak shape and
size from island to island.
He reasoned these differences made
the finches better adapted to the food
in their particular local environment.
Each finch population had developed
beaks which were suitable for that
particular environment.
Phylogenic Tree
Phylogenic trees trace
patterns of shared
ancestry between
lineages.
Each lineage has a
part of its history that
is unique to it alone
and parts that are
shared with other
lineages.
Limits of Natural Selection

Natural selection works

on existing variation in a population

It could not account for the origin of variations
 Critics reasoned that should a variant trait arise,


it would blend with other traits and would be lost
The answer to these criticisms
existed even then in the work of Gregor Mendel,
 but remained obscure until 1900

Evidence of Change
Fossil Record
 Embryology
 Molecular Biology-Amino Acids,
Nucleotides, DNA sequencing,
mitochondrial DNA
 Anatomy commonalities
 Various adaptations

EVIDENCE OF EVOLUTION

STRUCTURAL ADAPTATIONS
 MIMICRY
 CAMOUFLAGE
http://evolution.berkeley.edu/evolibrary/home.php
http://science.howstuffworks.com/animal-camouflage2.htm
Fossil Record
Fossils are a major source of
information about changes in
life during the
distant past
 In general, fossils
show that life has
increased in
diversity and complexity
over time

Fossil Record

Interpretation of the distribution of fossils in the rock
initially based on the principle of superposition
- in undisturbed rock layers, older fossils will be
found lower in the rock than younger fossils
-radiometric dating confirms this

In general older life forms tend to be less complex
Periods of diversity are interrupted by mass
extinctions – followed by new life forms
Fossil Record is incomplete – estimated only 1 in
10,000 extinct species are represented – Why?


Embryology



All vertebrate embryos have
 Gill slits on sides of the throat
 Post anal tail
The fact that organisms without gills, or tails have
them as embryos is taken as evidence of a common
ancestry with organisms that had both
Which is the fish, rabbit, human, chicken, tortoise?
Comparative Anatomy

Similarities in
structure between
organisms was used
to determine
evolutionary
relationships
Other Proof From Anatomy

Vestigial structures – structures that are
greatly reduced with little or no function
- they are thought to be left over from
ancestors
 Pelvis and leg bones in snakes
 Reduced toe in horse
 Appendix in human
 Coccyx (tail bone) in humans
Vestigial Structures
Comparative Anatomy

Analogous Structures
 Similar function but
different structure  Insect’s wing, Bird’s
wing and Bats wings
– all allow flight, but
are structurally different
 Eyes of Mollusks and
Vertebrates – both allow
sight, but are different
in structure
Comparative Anatomy

Homologous Structures

Have a similar structure but different
function
The forelimbs of vertebrate animals all have
the same structural design, but they have
different functions
 This similarity of structure shows a common
ancestry

Homologous Structures
Analogous structures
Molecular Biology
Comparisons of the sequences of amino
acids in proteins or nucleotides in DNA
can show the relationships between
organisms
the number of differences in the
sequences of amino acids or
nucleotides indicates how closely
related two organisms are
Hemoglobin Comparison
Species
Gorilla
AA differences from humans
1
Rhesus Monkey
8
Mouse
27
Chicken
45
Frog
67
Hemoglobin Cladogram
Cladogram (family tree)
created from a fossil record
Bird Evolutionary Tree
Phylogenic Trees
and Cladograms
are also created
using comparative
DNA sequences.
If the DNA is very
similar to each
other, it means they
share a fairly
recent common
ancestor.
Darwin Developed the Theory
During his voyage, Darwin observed fossil
mammals in South America that are similar to
yet different from present day animals.
Ex. Llamas, sloths, and armadillos.
The finches and giant tortoises lining on the
Galapagos Islands vary from South America,
even though they differ in subtle ways.
These observations convinced Darwin that
organisms descended with modification from
ancestors that lived during the past which was
his central claim of the theory of evolution.
Charles Darwin
Alfred Wallace

Descent with modification.

The Origin of Species. 1859


Species were not created in their present forms
but evolved from an ancestral species.
Natural selection, the
mechanism by which
change occurs (Explanation
of how evolution occurs).
Darwin and Wallace

Darwin and Alfred Russel Wallace
(1823-1913)
read John Malthus’ book
 and came to the same conclusion,


that a natural process


was selecting only a few individuals for survival
Darwin’s and Wallace’s idea
called natural selection
 was presented simultaneously in 1859
