Transcript Darwin and His Theory

Evolution
Nothing in biology makes sense except in
the light of evolution. – Theodosius
Dobzhansky
Charles Darwin in later years
What is Evolution?
The kind we’re talking about is sometimes called organic evolution to distinguish it
from non-biological changes over time.
Working definition: Evolution is the progressive change in populations over time.
NOT SPECIES, NOT INDIVIDUALS
Evolution Holds a Unique Place in Biology
Other disciplines ask how?
Evolutionary biology asks why?
Evolution’s Core Principles
Natural selection.
Evolution’s Core Principles
Common descent with modification.
Evolutionary Time Scales
Macroevolution: Long time scale events
that create and eliminate species.
Evolutionary Time Scales
Microevolution: Short time scale events (generation-to-generation) that change
the genotypes and phenotypes of populations.
We’ll begin our more intensive look at evolution with microevolution.
Darwin’s Voyage of Discovery
A reconstruction of the HMS Beagle sailing off Patagonia.
The Voyage of the Beagle
Darwin’s Ideas Did Not Develop in a Vacuum
Contributor’s to Darwin’s thinking included:
Charles Lyell –(geologist) uniformatarianism.
The Earth is older than 6,000 years
1797-1875
Georges Cuvier – species extinction.
Fossils
1769-1832
Darwin’s Ideas Did Not Develop in a Vacuum
Contributor’s to Darwin’s thinking included:
Thomas Malthus – struggle for existence.
Carrying capacity: J curve/S curve
1766-1834
Jean Baptiste de Lamarck – evolution by
acquired characteristics. First evolution
Theory, Giraffes get taller due to stretching
In parents
1744-1829
Alfred Russel Wallace Independently Drew the Same
Conclusions as Darwin
Papers from Wallace and Darwin were jointly presented (with little
impact) to the Linnaean Society in 1858.
Haeckel: ontogeny recapitulates
phylogeny
• Thomas Hunt Morgan: Darwin’s bulldog
Darwin’s Observations and Inferences
Organized by Ernst Mayr
Observation 1: Left unchecked, the number of
organisms of each species will increase exponentially,
generation to generation.
Observation 2: In nature, populations tend to remain
stable in size.
Observation 3: Environmental resources are limited.
Inference 1: Production of more individuals than can be supported by the
environment leads to a struggle for existence among individuals, with only a
fraction of offspring surviving in each generation.
Darwin’s Observations and Inferences
Observation 4: Individuals of a population vary extensively in their characteristics
with no two individuals being exactly alike.
Observation 5: Much of this variation between individuals is heritable.
Darwin’s Observations and Inferences
Inference 2: Survival in the struggle for
existence is not random, but depends in
part on the heritable characteristics of
individuals. Individuals who inherit
characteristics most fit for their
environment are likely to leave more
offspring than less fit individuals.
Darwin’s Observations and Inferences
Inference 3: The unequal ability of individuals to survive and reproduce leads to a
gradual change in a population, with favorable characteristics accumulating over
generations (natural selection).
Taken together, these three inferences are a statement of Darwin’s Theory of
Evolution.
The Weak Link of Genetics and the Modern Synthesis
A major problem in Darwin’s theory was the lack of a
mechanism to explain natural selection. (No mitosis,
meiosis, replication, chromosomes, laws of inheritance)
How could favorable variations be transmitted to later
generations?
With the rediscovery of Mendel’s work and its vast
extension in the first half of the 20th century, the missing
link in evolutionary theory was forged.
Darwin in his early
years.
Darwinian theory supported by genetics is known as the modern synthesis.
Discomfort With Evolution
The upheaval surrounding evolution began with
publication of On the Origin of Species and
continues nearly 150 years later.
An early disparaging
view of evolutionary
theory and its creator.
1925
Discomfort With Evolution
November, 2005
Discomfort With Evolution
December, 2005
Discomfort With Evolution
Two of many arguments made against
evolution are:
Evolution is only a theory.
No one’s ever seen evolution.
The first point is true, but misses the
meaning of scientific theory, and the
second point is easily countered.
Evidence for Evolution – The Fossil Record
Evidence for Evolution - Comparative Morphology
Homologous structures
Why use the same skeletal plan for these very different appendages?
Evidence for Evolution - Comparative Embryology
Why do embryos of different animals pass through a similar developmental stage?
Recent discoveries of the conservation of molecular mechanisms of development are
even more compelling.
Evidence of
Evolution –
Conservation and
Diversification at
the Molecular
Level
Why should
different
organism possess
related genes?
Why does the
degree of
relationship of
genes match their
degree of
relationship
established by
other methods?
Evidence for Evolution –
Evolution Observed
Evolution of pesticide resistance
in response to selection.
Evidence for Evolution – Evolution Observed
Evolution of drug-resistance in HIV
Modes of Selection
Special Examples
• Kin Selection: relative fitness includes fitness of close
relatives
• Artificial selection: farming/animal breeding
• Sexual selection: based on mating
• Convergent evolution: different ancestor common lifestyle
(analogous structures result)
• Divergent evolution: common ancestor different lifestyle
(homologous structures result)
• Parallel evolution: evolving in the same pattern
• Coevolution: two evolving each other
Speciation
– Steps in the process:
» Subdivision of the population
» Evolution of each subpopulation in independent
directions
» Change in population that reproductively isolates the
population from the other.
» Return to same setting and no longer can members of
the two populations mate.
Speciation
• Allopatric:
Geographical
separation leads to
initial subdivision of
the population.
• Rivers, volcanoes,
earthquakes, roads,
train lines, etc..
Sympatric speciation
• Sympatric: Isolation
of populations occurs
while organisms have
physical contact with
each other.
More sympatric
• Apple maggot flies
Temporal/Sympatric speciation
Reproductive Isolation
• Prezygotic vs. Postzygotic
• Needed for speciation: Organisms can look
somewhat different and still be one species if this
does not occur.
• Organisms can look very much alike, but be two
species if this occurs.
• The idea is that eventually diversity will build up
in the populations independently and thus would
eventually look different.
Many Intrinsic Reproductive Isolating Mechanisms Drive
Speciation
Courtship rituals, like
these, are critical for
mating within a species,
but ineffective for
attracting members of
other species.
Behavioral Isolation Mechanisms
Courtship rituals, like these, are critical for mating within a species, but
ineffective for attracting members of other species.
Many Intrinsic Reproductive Isolating Mechanisms Drive
Speciation
(different habits within an overlapping range)
Many Intrinsic Reproductive Isolating Mechanisms Drive
Speciation
Many Intrinsic Reproductive Isolating Mechanisms Drive
Speciation
Speciation Dynamics - Gradualism or Punctuated Equilibrium?
Punctuated equilibrium appears
to be a more accurate view of
speciation dynamics.
: long period lacking speciation
where variation builds up
followed by some dramatic
change in the environment that
leads to a struggle for survival
and lots of speciation and
microevolution.
Evolution possibilities
• Convergent evolution: leads to analogous
structures. (same function/different ancestry)
Parallel evolution vs. Coevolution
• A: divergent B: convergent
C. parallel
Divergent evolution
• Divergent evolution: leads to homologous
structures. (same ancestry/different function)
Coevolution
• Yucca moth and Yucca flower
Does coadaptation mean
coevolution?