Lecture 01: The synthetic theory of evolution

Question 1

Evolution def.

Answer 1

Evolution describes the heritable changes in populations over time

• the preconditions for evolution are:
  1) Inherited similarity -> Evolution is a historical process
  2) Variation
  3) Selection
• evolvere [lat.]: to unroll develop based on something already existing
• Descent with modification: All species have evolved from one single common ancestor and have then accumulated modifications through time which make all lineages different in the present.
• This implies that not only are we related to other mammals but also to mushrooms and bacteria!!! (imagine the response of society when this ideas came out for the first time!!)

Descent with modofication: Abstammung mit veränderungen

Question 2

Before Darwin

Answer 2

Organic progression / Lamarckism

• How did the giraffe get its long neck?
• Continuous stretching of neck and the inheritance of acquired/achieved trait

Question 3

Preconditions for evolution

Answer 3

1) Inherited similarity -> Evolution is a historical process

• Mendel discovered traits can skip a generation
  ->Trait based on few tightly linked genes, no environmental influence
  -> Common: _ Trait based on many gene loci(QTLs)
  _ Environment impacts trait

2) Variation
3) Selection

Question 4

Plasticity or inherited change?

Answer 4

• Phenotypic plasticity => morphological difference caused by the environment (heritability h^2= 0)
• Difference purely genetic => morphological difference genetically determined (heritability h^2= 1)
• Heritability: h^2 = VGenotype/VPhenotype
• Example: Common garden experiment

-> Ratio between variability due to differences in genotypes to total phenotypic variability
* Both, h2 = 0 and h2 = 1 are rare
* Common: traits are based on multiple gene loci (QTLs) AND environment impacts traits

Question 5

Mendelians vs. Darwinians

Answer 5

Mendelians:
Principles
* new species through single mutations
* natural selection is old fashioned speculation
* mutation and selection are mutually exclusive
* only discrete variation relevant
Side note:
* focussed on „single gene“ traits
* quantitative genetics unknown

Darwinians:
Principles:
* phenotypic variation
* limited resources
* survival of the fittest (natural selection)
Side note:
* no genetics
* focussed on quantitative traits

Question 6

Synthetic theory of evolution (origin 1930-1950)

Answer 6

Evolutionary theory (Charles Darwin & Ernst Haeckel) meets genetics (Mendel, De Vries & Morgan)

„Mutations create the variation, which selection acts upon“

Theodosius Dobzhansky (Russian geneticist; 1900-1975):
- 1927 emigrated to USA
- „Genetics and the origin of species“ (1937) biological species concept

Sir Julian Huxley (English biologist; 1887-1975):
- „Evolution, the modern synthesis“ (1942)

Question 7

Principles of evolution

Answer 7

1. Evolution as a historical process -> inheritance
Ancestor of whale before going back into the water -> breathing with lungs
=> Constraint by previous adaptations

2. No design in variation -> unpredictable mutations
Direct mutation
Random mutation
=> No predictable course of adaptation

3. Selection occurs by differential survival/ reproduction of different genotypes
Experimental evolution of learning ability in fruit flies
Higher learning ability causes higher reproduction („fitness“)

4. Selection leads to adaptation
Local adaptation in Poecilia Mexicana to sulphides -> Plasticity or inherited change?

Question 8

How did the giraffe get its long neck? - Synthetic theory of Evolution

Answer 8

• „Mutations create the variation, which selection acts upon“
• Neck length is a phenotypically variable quantitative trait
• Part of the variation in neck length is based on genetic variation
• Individuals with longer necks have a higher fitness (more offspring)
• This selection on phenotypes increases frequency of alleles positively correlated with neck length