Evolution

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Evolution

• Only a theory?

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Basic premises for this discussion

• Evolution is not a belief system. It is a
  scientific concept. It has no role in defining
  religion or religious beliefs
• Evolution is a theorybut you dont get any
  better than that in science
• There is a lot of contention about evolution, but
  not among scientists or scientific organizations.

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Some basic definitions

• Fact an observation that has been repeatedly
  confirmed
• Law a descriptive generalization about how the
  physical world behaves
• Hypothesis a testable statement that can be used
  to build inferences and explanations

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Some basic definitions

• Theory a well-substantiated explanation that
  incorporates facts, laws, inferences and tested
  hypotheses.

In science, you dont get any better than a
theory.
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What is evolution?
A basic definition of evolution
evolution can be precisely defined as any
change in the frequency of alleles within a gene
pool from one generation to the next." - Helena
Curtis and N. Sue Barnes, Biology, 5th ed. 1989
Worth Publishers, p.974
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So what does the definition mean?

• Evolution is a change in the number of times
  specific genes that code for specific
  characteristics occur within an interbreeding
  population
• Individuals dont evolve, populations do
• There is no implied improvement in evolution

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Another way to define it

• A process in which heritable characteristics of
  a population accumulate over time

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Evolutions Core Principles
Descent with modification
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Evolutions Core Principles

• Natural Selection
• (differential reproductive success)

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Evolutions Core Principles

• Evolutionary adaptations
• a prevalence of inherited characteristics that
  enhance organisms survival and reproduction

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Natural Selection Affects IndividualsEvolution
Affects Populations
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Darwin did not work in a vacuum
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Darwins Voyage of Discovery
A reconstruction of the HMS Beagle sailing off
Patagonia.
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The Voyage of the Beagle
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Darwins Observations and Inferences

• 1st Observation
• All species have such great potential fertility
  that their population size would increase
  exponentially if all individuals that are born
  reproduced successfully.

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Darwins Observations continued

• 2nd Observation
• Populations tend to remain stable in size,
  excepting seasonal fluctuations.
• 3rd Observation
• Environmental resources are limited

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Darwins Observations continued

• 4th Observation
• Individuals of a population vary extensively in
  their characteristics no two individuals are
  exactly alike.
• 5th Observation
• Much of this variation
• is heritable.

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Darwins Inferences

• Inference 1
• Production of more individuals than the
  environment can support leads to a struggle for
  existence among individuals of a population, with
  only a fraction of offspring surviving each
  generation.

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Darwins Inferences

• Inference 2
• Survival in the struggle for existence is not
  random, but depends in part on the hereditary
  constitution of the individuals. Those
  individuals whose inherited traits best fit them
  to their environments are likely to leave more
  offspring than less fit individuals.

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Darwins Inferences

• Inference 3
• This unequal ability of individuals to survive
  and reproduce will lead to a gradual change in a
  population with favorable characteristics
  accumulating over the generations.

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Evolution evidence Biogeography

• Geographical distribution of species
• Examples Islands vs. Mainland
• Australia Continents

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Evolution evidence The Fossil Record

• Succession of forms over time
• Transitional links
• Vertebrate descent

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Evolution evidence Comparative Anatomy

• Homologous structures (homology)
• Descent from a common ancestor
• Vestigial organs Ex whale/snake
  hindlimbs wings on flightless birds

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Evolution evidence Comparative Embryology

• Pharyngeal pouches, tails as embryos

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Evolution evidence Molecular Biology

• Similarities in DNA,
• proteins and genes
• Common genetic
• code

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• Absence of evidence is not evidence of absence.
• Carl Sagan