Lecture 1: Introduction to Evolution

1
Lecture 1 Introduction to Evolution

• Evolution change in allele frequencies in a
  population
• Great, is class over now?
• No (sigh), because the process results are
  interesting important to our understanding of
  biology

2
Questions in evolution

• WHY is life on earth diverse?
• (well get to this later)
• HOW is life adapted ?
• (questions leading to more questions)

3
Adaptation Questions

• Are all traits adaptive?
• Are all adaptations perfect?
• Who/what benefits from adaptation?
• Where did all these questions come from?

4
BD Before Darwin

• Orthodoxy species as fixed, designed by God
• Bible literal truth
• variation imperfection
• BUT, even before Darwin this was questioned
• Idea of changeable/old Universe, allowed idea of
  changeable life on earth (geology paleontology)
• Enlightenment fossils spontaneous generation,
  transmutation

5
Lamarck

• spp. change into new spp. over time
• Transformism Acquired Characters
• -no branching e.g. Giraffes neck
• -no extinction
• So, Darwin had somewhere to start

6
Darwin (1809-1882)

• Noticed geographic variation in very similar
  spp.
• Rejected orthodoxy b/c did not explain
  adaptation
• Theory why spp. change why they are well
  designed for their lives
• Influences
• Malthus (population principle)
• Lyell (continuous change vs. catastrophists)
• Social influences (materialism)

7
Darwins conclusion

• Struggle for existence only some survive
• Expect favourable variations to survive
• Natural Selection
• Mechanism most important aspect of theory
• Poor Alfred Russel Wallace same conclusions on
  a much smaller budget
• Co-presented the idea but Darwin is remembered
  because of The Origin of Species

8
Darwins Dangerous Idea

• The Origin of Species (1859)
• Theses
• Descent with Modification from Common Ancestors
  (Evolution)
• Natural Selection is main agent of Evolution

9
Origin in a nutshell

• Observed overproduction of offspring
• Many born few survive to reproduce
• WHY?
• Limited resources popns limited in size
• Therefore STRUGGLE FOR EXISTENCE

10

• 2. Individuals vary
• If competition for resources then only
  favourable variants survive to reproduce
• 3. Most of the variation is inherited
• (e.g. domestic species sexual reprodiversity)
• Favourable variants have more offspring
  increase in frequency
• Change in the population over time
• Plus lots about pigeons

11
Deduction
Descent with modification via natural
selection Testable???
Comparative Anatomy
Fossil Record
Predictions
Comparative Embryology
Behaviour
Geographic Distribution
12
Why Dangerous?

• Static ? dynamic view of nature
• Creationism implausible
• Platonic essentialism
• variation basic/neutral feature
• Refuted teleology anthropocentrism
• Natural Selection
• No goal
• No consistent direction
• EVOLUTION ? PROGRESS

13
Evolution is a bush not a ladder
Humans
Mammals
Birds
Amphibians
Fish
14
Reception

• Evolution generally accepted but
• Viewed as progressive (towards a goal)
• Natural selection rejected
• No theory of heredity
• (how characteristics passed on)
• Problem of uncrossable gaps in evolution
• Back to transmutation

15
The Modern Synthesis

• Mendelian genetics rediscovered in 1920s
• By 30s/40s widely accepted
• acquired characters not inherited
• Continuous variation explained by Mendelian
  genetics (Fisher)
• Theoretical works show N.S. can work with what is
  available in nature, nothing else required
  Speciation only requires N.S. not macromutation
  /acquired characters
• Species are not morphotypes dynamic concept

16
Tenets of Modern Synthesis

• Populations have variation from random, not
  adaptively directed, mutation recombination
• Populations evolve through changes in gene
  frequency by drift, gene flow N.S.
• Change is gradual because most genetic variants
  have slight effects on phenotype
• Diversification (speciation) is due to gradual
  reproductive isolation among populations
• Overtime, changes give rise to new taxa

17
Geneticsmore important than Darwin?

• After Darwin, many accepted the idea of evolution
  as change in species over time
• BUT, much argument against NS
• Genetics forced the rejection of evolution as
  goal-oriented the widespread acceptance of NS

18
Modern Evolutionary Biology

• Two principle goals
• Inferring history of evolution
• Elucidating the mechanisms
• Modern evolutionary theory
• Provide explanation for patterns of life in
  space time the processes by which these
  patterns arose