Natural Selection

The problem: How does one explain the great functionality of so many different species?
The answer: Natural Selection

Definition of natural selection:
Differences in reproductive success that result from heritable differences between individuals.

Particulate heredity/Mendelian genetics:
Genes do not all blend: some behave as we think today, i.e. dominant/recessive. When people put together the gene discoveries along with Darwin's ideas they got it.

3 Types of Natural Selection:

Stabilizing Selection-- The extremes are selected against.
Example: height; mostly beings tend to the average height- not too many really short ones or really tall ones.

Directional selection-- One extreme value is selected for.
Example: speed; faster is always better so a population will tend to get faster over time.

Disruptive selection-- The extremes are both selected for.
This type of selection is not as common as the first two. Example: Prey-type animal with distinctive markings which the predators know will over time move away from the norm in both directions.

Micro- vs. Macro- Evolution
micro= Short-term, small changes that we can observe
macro= Big changes over long-term that we can't really observe

Taxonomy is a difficult problem. There are millions of different ways to classify all the living things on earth. But if we classify according to evolutionary relations, then there is really only one right way. We may argue about what is more closely related to what since we don't know what the right answers are, but there is only one ultimate truth.

A little on sexual selection: (more detail will be forthcoming in a later lecture)
The catch-phrase shouldn't be survival of the fittest, but reproduction of the fittest. You only need to survive long enough to breed. Prolificness is better than longevity: Animals who live a long time but don't rear many young will be overrun by animals who live short lives but multiply better. This'll show up in female choice and male-male competition.
How did such a catch-phrase come about? (No, Darwin didn't invent it- one of his later proponents did.) "Fitness" in the olden days used to mean how the organism fit into its environment. Now it just means how well it can reproduce.

The gene as a unit of selection: Dawkins' 'The Selfish Gene'
Think not of individuals as being selected for, but genes as being selected for. Individuals don't make exact copies of themselves, but genes do. So, you may ask, where does altruism come from? How come any mutation which causes altruism doesn't just get selected right the heck out of there? Think about it this way: If you sacrifice your life for 1 sibling, then only half your genes get passed on. This doesn't bode well for your genes. However, if you sacrifice your life for three siblings, then 1.5 copies of your stuff get passed on so this altruistic gene would survive better than a selfish gene. This leads to:

Hamilton's equation: Which determines whether an individual will be altruistic.
C < r B
In English, Cost should be less than the Benefit times the Relatedness.

So if you have an opportunity to sacrifice yourself for a sibling, who is 1/2 related to you, then you'll sacrifice only if his benefit is more than twice your cost. (Because altruism genes who didn't follow this equation wouldn't have gotten passed along as much as genes who did.)
(Hamilton's is not to be tested)

Common misunderstandings of evolutionary theory:

Group selection: Entire groups do *not* limit their reproduction for the good of the group. A single mutation would quickly take over the population. A group can't be selected really, unless it's completely isolated which is really rare.

Evolution should lead to perfection: You might think to yourself, "Why after all these years isn't everything perfect? Take primates with a prehensile tail; wouldn't it be better to just have some more arms? How come evolution hasn't made arms?" The problem is, that particular variation wasn't present in the population to work with- only genes which are present can be selected and refined.
Another example: smarter is better, right? So how come all animals aren't so smart? Well actually brains use a lot of fuel and lots of animals don't even need 'em.

Evolution is striving for a specific goal: Good evolutionists don't use the terms 'higher' and 'lower.' Certain organisms are not inherently better than others. Other organisms are not sitting around in primordial soups trying to evolve into humans.

And here, by the special request of my grandfather, is the paper I wrote on natural selection for this class.