(Stebbins 1971, modified by Kutschera & Niklas 1994)

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*

* ?

Stochasticity in Evolutionary Biology

“When we look at the plants and bushes clothing an entangled bank, we are tempted to attribute their proportional numbers and kinds to what we call chance. But how false a view is this!”

“…the idea that chance begets order…”(Peirce 1893, quoted in Beatty 1984)

Beatty, J. 1984. Chance and natural selection. Philosophy of Science 51:183-211.

Random with respect to…

Key insight into evolution: Particulate inheritance

Deterministic effects: genes to genotypes to phenotypes

Fisher Wright Haldane

Particulate Inheritance (Mendel) + Evolution by Natural Selection (Darwin) =

The Modern Synthesis

Population genetics theory built from scratch

4 processes: Drift (N), Mutation (), Gene Flow (m), Selection (s)

Consensus on theoretical possibilities, and the “right” model structure

Disagreement on the relative importance of different processes in Nature

The Evolutionary Modern Synthesis

(Stebbins 1971, modified by Kutschera & Niklas 1994)

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*

* ?

* Processes with stochastic elements

Consensus on theoretical possibilities, and the “right” model structure

Disagreement on the relative importance of different processes in Nature

The Molecular Revolution:

Evolution at the level of proteins/DNA

Why so much variation?

Shouldn’t it get edited out by natural selection?

Mootoo Kimura

Maybe much of this variation isn’t even “seen” by natural selection

The neutral theory of molecular evolution:

Mutation, Drift, Gene flow

Many DNA changes do not alter the amino-acid composition of a protein

Some (many?, few?) amino acid substitutions don’t alter the function of a protein

Each one of these loci (some neutral, some not) has the exact same demographic history (i.e., drift, migration)

The neutral theory of molecular evolution is operational(in a way that the ecological theory is not)

The neutral theory of molecular evolution is operationalAn example: Selective sweeps

Okay, so all these processes are happening in Nature…but what is their relative importance?

Does the answer really matter?

Beatty, J. 1984. Chance and natural selection. Philosophy of Science 51:183-211.

On relative importance:

Beatty, J. (1997) Why do biologists argue like they do? 64:S432-S443.

The importance (or not) of debates about relative importance

The reason evolutionary biology seems to rest on more solid theoretical footing than ecology, is because

evolutionary biologists agree on the theoretical framework, not the relative importance of different processes.

Regional community

Dispersal

SpeciationDrift

Selection

Dispersal

LocalCommunity

SpeciationDrift

Selection

Dispersal

Global community

Dispersal

SpeciationDrift

Selection

Note: Extinction results from drift & selection

Everything you need to know… …about ecological communities

The Tree of Life Projecthttp://tolweb.org/tree/

Darwin’s first phylogeny

What about macroevolution?

A critique of assuming determinism

Stephen J. Gould and “contingency”

A critique of assuming gradualism

Replaying Life’s Tape

“I call this experiment “replaying life’s tape.” You press the rewind button…go back to any time and place in the past…Then let the tape run again and see if the repetition looks at all like the original”

“any replay of the tape would lead evolution down a pathway radically different from the road actually taken”

Contingency(= stochasticity?)

Are the shapes of phylogenies different from random expectation?

Are the shapes of phylogenies different from random expectation?

Looks like we got null models from evolution too (in addition to neutral models)

Lessons for Community Ecology:

• Can neutral theory be “operationalized”?

• Perhaps we can at least agree on a conceptual framework (mine, of course)

• Can we skip past the mind-numbingly obvious aspects of the selection-neutrality debate?

• Where is the “relative importance” approach going to get us?

•Building models and empirical studies to be more comparable to one another.

• Getting drift into models of selection…to come next week