Transcript Evolution
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