What is Evolution?

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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

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”

What causes evolution?

a) Natural selection b) Mutation c) Genetic drift, or neutral, random evolution e) Migration, or gene flow

This lecture: simple examples of evolution by natural selection

What is natural selection?

“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

Evolution, a fact?

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

Science: prediction

According to Karl Popper: science is falsifiable.

Falsehoods disprovable; truth more difficult!

Religion: truth is by faith. Very different.

Selection and the single gene

“Quantitative traits” (e.g. size, behaviour): usually multiple loci

Single-locus traits: great examples of evolution by natural selection

Many single-locus traits are involved in resistance to stress (often humans )

Examples of single-gene traits

• Industrial melanism in moths (resistance to urban pollution)

• Heavy metal tolerance in plants growing in mine tailings

• Malaria resistance in humans (sickle-cell haemoglobin, etc.)

• Pesticide resistance (mosquitoes, insects, weeds, fungi, warfarin resistance in rats)

• Antibiotic resistance in bacteria

We used to do this for tutorial; there are many references on reserve, still; see eUCLid

The peppered moth Biston betularia

Left: form typica (left, and carbonaria (right) on lichen-covered trunk in Dorset.

Right: on soot-covered tree near Birmingham

How does evolution by natural selection work?

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!

A flow diagram for

Random mating

Offspring genotypes in

Hardy-Weinberg ratios

Natural selection

Offspring after selection

So now you can write an evolution computer program!

Numerical vs. analytical theory

Take-home points

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

Further reading

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

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