What is Evolution?. Produces biological diversity - DNA sequence variation - Bacteria - Flowering plants - Sexual selection in birds - Human civilization Evolutionary Genetics: mechanisms Science: understanding; predictions. Evolution: definition.
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Produces biological diversity
- DNA sequence variation
- Flowering plants
- Sexual selection in birds
- Human civilization
Darwin:"descent with modification“
A change in morphology, ecology, behaviour, physiology
Change must be genetic
Modern, genetic definition:
“evolution is change in gene frequencies between generations”
“a consistent bias in survival or fertility between genotypes within generations”
Selection often causes evolution, but may also prevent evolution (e.g. stable polymorphism)
Evolution does not require selection (e.g. drift -- important: > 95% of genome maybe "junk"!)
However, many interesting types of evolution involve natural selection
You don’t have to believe in evolution to take this course, but you do have to know the arguments to get a good grade!
Evolution is a fact, and it’s hard to ignore
… but, theory and fact: not so different
According to Karl Popper: science is falsifiable. Falsehoods disprovable; truth more difficult!
Religion: truth is by faith. Very different.
“Quantitative traits” (e.g. size, behaviour):
usually multiple loci
great examples of evolution by natural selection
Many single-locus traits are involved in
resistance to stress (often humans)
We used to do this for tutorial; there are many references on reserve, still; see eUCLid
Left: form typica (left, and
carbonaria (right) on lichen-covered
trunk in Dorset.
Right: on soot-covered tree near Birmingham
Evolution by natural selection is an inevitable, mathematical process.
The frequency of a particular allele will change, and its rate of change will depend mathematically on the advantage (or relative fitness) of that allele.
Mathematical evolutionary theory is useful. For example, given information about natural selection, how rapidly will evolution occur?
The answers help us understand antibiotic resistance, or pest resistance, for instance.
Evolution is a predictive science! Useful, as well as fun!
Offspring genotypes in
Offspring after selection
So now you can write an
evolution computer program!
Numerical vs. analytical theory
Evolution to a geneticist: a change in gene frequencies.
Natural selection: a consistent bias favouring some genotypes over others.
Evolution can occur in the absence of natural selection, via genetic drift or neutral evolution.
Natural selection can stabilize the status quo; zero evolution.
Evolution at a single dominant gene: rate can be predicted
If selected, dominant alleles evolve quickly when rare, slowly when common; recessive alleles evolve slowly when rare, quickly when common.
We can estimate selection coefficients (s), fitnesses (W=1-s) and predict rates of evolution from data on survival or fecundity.
Mathematical theory makes evolution a predictive science
FUTUYMA, DJ 1998. Evolutionary Biology. Chapters 12 and 13 (pp. 371-381).
References on natural selection at single genes for resistance (see web)
Science Lbrary: View B242 Teaching Collection by going to eUCLid; use Keyword, Basic Search, All Fields: B242