Download L1: Descent with Modification

Biodiversity
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Globally - ~1.8 million
species
~10,000 birds
~ 4629 mammals
~ 8240 reptiles
~ 900,000 insects (named)
~ 300,000 vascular plants
~ 20,000 fish
Descent with Modification
Lecture 1
Winter 2014
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Species Diversity & Unity
Species Diversity & Unity
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• Hierarchy of
classification
• What are some of the
characteristics shared
by all life?
• Organisms suited to their
environment
Fig. 22.12
• Need a theory (model)
that can explain these
patterns
See Fig. 26.3
Themes in Biology
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• Charles Darwin (1809-1882)
• 1831-1836 – Voyage of the HMS Beagle
Evolution is the
theme that unifies
all biology
“Nothing in biology
makes sense
except in the light of
evolution”
- Theodosius
Dobzhansky
Darwin’s Journey
See Fig. 1.22
Fig. 22.5
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Historical Context of Darwin’s Work
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Plato & Aristotle (384-322 B.C.)
• Species are fixed
• Ladder of life (scale of nature)
Special Creation/Natural Theology (JudeoChristian)
• The world is ~ 6000 years old
• Species represent independent/separate entities
• Species are fixed
Carolus Linnaeus (1707-1778)
• Taxonomic system based on similarities
Historical Context of Darwin’s Work
– Events in the past happened suddenly
– Mechanisms of change in the past are different than
those operating today
James Hutton (1726-1797) - Geologist
• Gradualism (1795)
– Change occurs through slow, continuous process
– Mechanisms of change still occurring today
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– Human population has the potential to grow faster
than food supply
Historical Context of Darwin’s Work
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Jean-Baptiste de Lamarck (1744-1820) Naturalist
• Proposed that species have changed through
time and are related by common ancestry (1809)
• Mechanism - Inheritance of acquired
characteristics
– Mechanisms of
change are constant
over time
– Earth older than
proposed
• Thomas Malthus (1766-1834) Economist
• 1798 – “An Essay on the Principle of Population
as it affects the Future Improvement of Society”
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Georges Cuvier (1769-1832) - Paleontologist
• Documented succession of fossils
• Catastrophism
Charles Lyell (17971875) - Geologist
• Uniformitarianism
Historical Context of Darwin’s Work
Historical Context of Darwin’s Work
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Darwin’s Work
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Darwin observed patterns
• Descent with Modification
– Species are related by common ancestry
– Species change through time
Darwin proposed a process
• Natural Selection
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Darwin’s Work
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• 1844 – Darwin writes essay on
evolution of species and natural
selection
• 1859 – Darwin publishes On the
Origin of Species by Means of
Natural Selection
• Explains the diversity and similarity of organisms
• Explains how organisms have come to be
adapted to a wide range of environments
Process = Natural selection
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Populations
Darwin’s Four postulates (criteria)
1. Individuals within a population vary in traits
2. Variation must be heritable (genes/DNA)
3. In every generation, more offspring are produced than
can survive. Only some individuals survive to
reproduce.
4. Survival and reproduction of individuals is not random
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Outcome of process: A Population’s characteristics will
change over time = Evolution will occur
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Evolution: a
genetically based
change in the
characteristics of a
population over time
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Population
• a group of individuals
of the same species
living in the same
area at the same time
• Typically breed within
the population
Individuals with certain heritable traits survive and produce
more offspring - they have been “naturally selected”
Evolution by Natural
Selection
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Evolution:
• Decent with modification
• A genetically based change in the characteristics
of a population over time
• 1858 –Alfred Russel Wallace
sends Darwin an essay
outlining the process of
evolution by natural selection
The Process: Natural Selection
The Theory of Evolution by Natural Selection
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The Theory of Evolution by Natural Selection
• What is “survival of the fittest”?
• Darwinian fitness (relative fitness)
– Ability of an individual to produce offspring,
relative to the ability in other individuals in the
population
– Measurable quantity
• Adaptation
– Any heritable trait that increases fitness of an
individual under prevailing environmental
conditions relative to individuals lacking this
trait
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Artificial Selection
Evolution by Natural
Selection
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What would happen to
this population if the
predator was a
mammal that could
see dark beetles more
easily than light
beetles?
See Fig. 22.9
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Evidence of Evolution
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Evolution in Action: Galapagos Finches
• Evolution is observable within our lifetime
– Antibiotic resistant bacteria
– Insects resistant to pesticides
– Plants resistant to herbicides
– Galapagos finches
• Evolution can be tested experimentally
• Finches on some of the Galapagos Islands studied
since early 1970’s
– Peter & Rosemary Grant
• Finch population had variation in many heritable
traits, including beak size
The Beak of the Finch. Jonathan Weiner.
1995
How and Why Species Multiply: The Radiation
of Darwin's Finches. Peter & Rosemary Grant.
2007
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Evolution in Action: Galapagos Finches
• Is there variation in this population?
• What is the average beak size?
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Evolution in Action: Galapagos Finches
Medium ground finches eat seeds
• Average rainfall year
– Wide variety of seeds
Beak Depth of
Medium
Ground Finch.
• Drought year
Year = 1976
• Wet Year
Population =
751
– Shrubs with large, hard seeds
– Shrubs overgrown by vines that
produce small seeds
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Evolution in Action: Galapagos Finches
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Evolution in Action: Galapagos Finches
1977 was a drought year.
• Make a prediction - what would happen to
the population size of the medium ground
finch from 1976 to the end of 1977?
• Were your predictions correct?
• Did evolution occur?
Beak Depth
of Medium
Ground
Finch.
Year = 1978
Population =
90
– Draw a graph illustrating your prediction
• Make a prediction – what would happen to
the beak depth of the medium ground
finch, if measured in 1978?
– Draw a graph illustrating your prediction
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Evolution in Action: Galapagos Finches
1983 was an extremely wet
year
What types of medium ground
finishes had the greatest
reproductive success?
(e.g., what characteristics
did they have?)
Evolution by Natural Selection
• Genetic diversity is key!
Ray Troll
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