Accounting for Biodiversity:
Evolution and Natural Selection
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History of the Theory of Evolution
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A Question of Biology or Culture
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νCharles Darwin’
Darwin’s grand
theory, evolution by
means of natural
selection, links diverse
biological facts into a
coherent whole. It is a
“unifying theory.”
theory.”
Yet,
we
remain
skeptical.
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Why?
Creation Concepts: The Fixity of Species
Evolution: Changes in biodiversity are observed
Catastrophism:
Catastrophism: Only a partial solution
Lamarck: Evolution by Use and Disuse
Darwin and Wallace: Descent and Modification
Evidence for Evolution by Natural Selection
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Artificial Selection
Fossil Record
Comparative Anatomy
Biochemical Analysis of Prot. and NA
Comparative Embryology
Biogeography and Adaptive Radiation
How do we account for life’s adaptive nature,
it’s many shared characteristics, and the
tremendous biodiversity we observe?
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1. The Fixity of Species (1700’s)
υ Natural theology and devine
creation
υ Linnaeus: taxonomic order
for the greater glory of God
2. Cuvier (1769-1832)
υ “Paleontology”- the
succession of fossils over the
ages
υ Catastrophism: accounting
for extinctions and the loss of
diversity
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Aristotle recognized
“affinities” that later on
coincided with Old
Testament ideas
Charles Darwin and the Golden
Thread (1809-1882)
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Ship’
Ship’s “naturalist”
naturalist” on HMS Beagle (1831(1831-1836)
Collected samples from S.America and the Galapagos
Considered the writings of:
υ James Hutton (Gradualism) & Charles Lyell
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(Uniformitarianism)
Uniformitarianism)
Thomas Malthus
Charles Darwin - Age and gradualism
Accepting the view that diversity
has changed over time…
3. Concepts of
Evolution: Erasmus
Darwin (late 1700’s)
4. Jean Baptiste Lamarck
(1809): Evolution by in
heritance of acquired
characteristics (I.e., by
use and disuse)
υ While he couldn’t
explain the
mechanism driving
evolution he still
recognized its value
in accounting for
biodiversity.
The historical context of Darwin’s life and
ideas
Darwin’s work put forward two
main ideas:
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The concept of evolution,
evolution, meaning that the
diversity of species on the earth today
arose by decent and modification of
ancestral species
That natural selection is the driving force
for adaptive evolution,
evolution, I.e., that the
modification of existing species results
from the interaction between each
individual’
individual’s inherited traits and the
environment leading to differential rates of
survival and reproduction
The net result: nonnon-random, environmentenvironmentdriven changes in the genetic makeup of
the population over time.
Observations and inferences cont’d
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Darwin’s Observations and
Inferences
Observation # 1 - Overproduction
υ Most populations have the potential to produce
many more offspring than the environment can
support with food, space and resources.
Observation #2 - Apart from seasonal fluctuations,
population sizes tend to remain stable.
Observations #3 - Environmental resources are limited.
Inference #1 - Production of more individuals than the
environment can support leads to a struggle for
existence among individuals resulting in differential
survival.
Summary of Darwin’s main points as published 1859:
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Observation #4 - Individuals in a population vary
extensively so that no two individuals are alike.
Observation #5 - Much of this variation is
heritable.
Inference #2 - There must be a struggle for
existence among individuals, where survival is, at
least in part, the result of heritable features of the
individual.
Inference #3 - There is differential reproductive
success between individuals, with those best suited
to the environment leaving a larger share of
offspring.
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Current examples of evolution abound:
Antibiotic and pesticide resistance
The diversity of species has arisen gradually over time by descent
and modification of existing species.
The differential survival imposed by the environment on individuals
individuals
carrying certain traits is called natural selection.
Natural selection acts on individuals as the modifying force.
All organisms living today are the consequences of the
environmental conditions faced by their ancestors.
The result is a change in the genetic makeup of the population over
time…
time…a classical definition for evolution.
Organisms appear well adapted to current conditions because these
these
resemble the conditions in which they evolved.
The theory does not predict perfect adaptation, it is not purposeful;
purposeful;
instead it yields the fittest available, the fittest yet, not the
the best
imaginable.
Variation: It arises randomly thru mutation and genetic mixing;
natural selection is nonnon-random because organisms evolve to match
their environment.
Over the past 150 years numerous lines
of evidence have taken Darwin’s idea to
the level of a unifying theory
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1. Artificial selection
2. Fossil record
3. Comparative anatomy
4. Comparative embryology
5. Comparative biochemistry
6. Biogeography
Artificial Selection
The Fossil Record:
A gallery of fossils
The branched evolution of horses
The Serendipity of Fossils
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Preservation
NonNon-compression
Mineralization
Elevation, Erosion
and Exposition
Basilosaurus: A transitional fossil linking past and present
Comparative Anatomy:
Homologous structures: anatomical signs of descent with modification
Convergent evolution and analogous structures
Comparative Embryology:
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Comparative Biochemistry:
Molecular Data and the Evolutionary Relationships of
Vertebrates
“Ontogeny recapitulates
phylogeny”
phylogeny” - the
appearance of ancestral
structures in the embryos
of modern descendants
(Haekel)
Haekel)
The Odyssey of Life
Molecular Biology as a tool for establishing homology:
Aligning segments of DNA and looking for the degree of
hybridization.
Molecular tools:
1. DNA-DNA Hybridization
2. Restriction Maps
3. DNA Sequence Analysis
Evolutionary convergence of marsupial and eutherian
(placental) mammals
Biogeographical Evidence: