Natural Selection v Evolution

1
Natural Selection v Evolution

• Evolution observed change in organisms over
  historic and geologic time
• Natural selection one hypothesized mechanism
  for change
• Has enormous body of supporting evidence

2
What is natural selection?

• Because organisms with greater reproductive
  success leave more offspring, they make a larger
  contribution to the gene pool. Any heritable
  characteristics that contribute to reproductive
  success will come to dominate the gene pool. The
  species changes in the direction of those
  characteristics.
• In other words, the currency of natural selection
  is BABIES. Survival is only important in
  promoting more babies.
• Natural selection occurs at the level of the
  INDIVIDUAL, not the species. Selection is driven
  by what is good for the individual, not what is
  good for the species.

3
Necessary conditions for natural selection to
occur

• There must be variation within the population.
• Variation from mutation, and from errors in
  sexual reproduction
• The variation must be heritable.
• The variation must change the likelihood of
  successful reproduction (including survival).

4
Elements in Reproductive Success

• Survival of parent better defense, better
  resource use, better adapted to physical
  environment
• Health and fertility adaptations maximizing the
  number of viable offspring
• Ability to attract mates sexual selection
• Can include characteristics that threaten
  survival, as long as they enhance the probability
  of attracting a mate
• Characteristic is a proxy for health or other
  positive characteristic

5
Elements in Reproductive Success

• Caring for young altruism and self-sacrifice
• Organisms may sacrifice themselves for relatives
  with whom they share a significant proportion of
  their genes
• Survival of young to reproductive age 2
  strategies
• Maternal care have a few offspring and invest a
  lot in caring for them (mammals)
• Independent offspring have a zillion of them
  and let them fend for themselves (plants,
  invertebrates)

6
The Evolution Wars

• Separating the scientific questions from the
  cultural scuffle

7
What is in dispute?

• In the cultural battle, evolution means many
  things
• Origin of the universe the Big Bang
• Origin of life
• Age of the earth
• Organic change within a species
• Origin of new species

8
What is in dispute?

• In science, evolution refers to specific
  things
• Origin of the universe the Big Bang
• Origin of life
• Age of the earth
• Organic change within a species
• Mechanisms natural selection, genetic drift
• Origin of new species
• Process speciation
• Mechanism reproductive isolation

9
Time out to review what we already learned and to
add a couple new things
10
Mechanisms for change

• Natural selection we already talked about
• Genetic drift when populations are separated
  from each other and their gene pools dont mix,
  variation that develops in each population will
  tend to make the populations more different
• E.g, variations in bird plumage, or lizard
  coloration. Or blonde scandanavians

11
Origin of new species

• Species set of populations that are actually or
  potentially interbreeding to produce fertile
  offspring
• Species are reproductively isolated from each
  other e.g., cannot successfully interbreed
• Speciation occurs when populations become
  reproductively isolated
• Geographically
• Other reason structural, chromosomal, chemical,
  behavioral

12
OK. THATS what scientists mean when they talk
about evolution. None of that other stuff.
Now on to other issues in the culture wars over
evolution.
13
Redefining science

• Science is based on predictability
• Since everything follows physical laws, we can
  predict what will happen, or explain what has
  happened
• No physical laws, no predictability no science
• Invoking supernatural explanations (creation
  science, intelligent design) inserts
  unpredictability you cant predict what a
  supernatural agent might do

14
From a purely pragmatic viewpoint

• Redefining science to include the supernatural
  removes the useful part of science
• For example, suppose we conjecture that demons
  cause disease.
• If its not testable, or we cant make
  predictions, were stopped dead we cant figure
  out what causes disease.
• And thats where humanity stalled out for several
  millennia until we took the supernatural out of
  our explanations of the natural world.

15
Dealing with popular misconceptions

• Evolution violates the 2nd law of thermodynamics,
  and is therefore impossible

16
Heres the three laws of thermodynamics

• Energy is neither created nor destroyed, just
  transferred
• Spontaneous natural systems cannot decrease in
  entropy (entropy disorder)
• Entropy decreases with temperature, and reaches a
  minimum at absolute zero.

17
Heres the three laws of thermodynamics

• Energy is neither created nor destroyed, just
  transferred
• Spontaneous natural systems cannot decrease in
  entropy (entropy disorder)
• Entropy decreases with temperature, and reaches a
  minimum at absolute zero.

18
But

• These laws do not say that systems cannot be
  self-organizing.
• Crystals are self-organizing systems
• Rivers are self-organizing systems
• The Earth is a self-organizing system (think
  plate tectonics)
• The overall trend in the entire system is toward
  increasing entropy (e.g., the entire Earth system
  tends toward entropy) but parts of the system may
  become more ordered

19
More misconceptions

• There are no intermediate forms in the fossil
  record. Therefore different kinds of organisms
  must represent separate creation events
• No, no, no. There are many spectacular examples
  of intermediate forms
• Fish to amphibians to reptiles
• Reptiles to birds
• Pre-humans to humans

20
Yet more misconceptions

• There are no examples of the gradual evolution of
  complex structures. If the structure only works
  when it is complicated, how could it possibly
  evolve from something simple?
• But the usual example given eyes is in fact a
  fabulous example of the evolution of a complex
  structure from simple light-sensing cells to a
  variety of independently evolved complex eyes
  (e.g., arthropod v. cephalopod v. vertebrate)

21
And anyway

• Evolutionary theory does not require the gradual
  evolution of different morphologies (forms or
  shapes)
• Two kinds of genes
• Structural genes code for proteins that build
  the structures
• Regulatory genes code for proteins that turn
  other genes on and off

22
Regulatory genes determine

• Fundamental body architecture (Hox genes)
• Bilateral v. radial is determined by 2 genes that
  either act in tandem or they dont
• E.g., starfish is bilateral as a baby and radial
  as an adult
• When features develop
• Babies and adults often look nothing like each
  other because of the sequencing of how genes turn
  on and off

23
Pisaster, the orange sea star
Baby
24
Regulatory genes determine

• Fundamental body architecture
• Bilateral v. radial is determined by 2 genes that
  either act in tandem or they dont
• E.g., starfish is bilateral as a baby and radial
  as an adult
• When features develop
• Babies and adults often look nothing like each
  other because of the sequencing of how genes turn
  on and off

25
Tunicates
26
Consider
The girl is 8 years old. She has primordial
dwarfism, a genetic endocrine disorder.
27
Or
Size in dogs can be controlled by a single gene.
Small genetic change, large morphological change.
28
So changes in regulatory genes

• Can change body shape dramatically in one
  generation
• Can create adults that look like juveniles

29
Consider
30
Consider
31
Neoteny

• Retention of juvenile physical traits into sexual
  maturity
• Dogs from wolves
• Humans from ape-like ancestor
• Vertebrates from tunicates