Natural Selection

Or, how did we get here….

Natural Selection

• The Theory of Natural Selection is so simple that anyone can misunderstand it…. (Anonymous)

• Charles Darwin (1809-1882) saw three problems in need of a solution. – Darwin was not the only one to see these problems BTW– Other ‘Naturalists’ were struggling with the same issues

Problem the First

• There is change over time in the flora and fauna of the Earth– What we would commonly call ‘evolution’ today– The fossil record showed this to be pretty clear,

even to people in the mid 1800s– This was not controversial in Darwin’s time, and is

not now.

The Second Problem

• There is a taxonomic relationship among living things– People were big into classifying stuff– It was pretty obvious that there was a relationship

between different species• Different birds, different grasses, different cats etc

The Third Problem

• Adaptation– Different kinds of teeth for different animals, say

carnivore ripping teeth and herbivore grinding teeth

– Different tissues within species• Heart vs. eye etc.

The Solution!

• Natural Selection provides a mechanistic account of how these things occurred and shows how they are intimately related.

• It is one of those ‘oh man is that ever easy, why didn’t I think of that?’ type things.

How’s it work?

• There is competition among living things– More are born or hatched or whatever, than survive and

reproduce

• Reproduction occurs with variation– This variation is heritable– Remember, there was NO genetics back then, Chuck

knew, he just knew….– Realized that is wasn’t ‘blending’

How’s it Work?

• Selection Determines which individuals enter the adult breeding population– This selection is done by the environment– Those which are best suited reproduce– They pass these well suited characteristics on to

their young

How’s it Work?

• REPRODUCTION is the key, not merely survival

• If you survive to be 128 but have no kids, you are not doing as well as I am

• I have reproduced…• Assuming the traits that

made me successful will help them then I amore fit NOW than the 127 year old guy

This lecture keeps evolving…..

• Survival of the Fittest (which Chucky D NEVER said) means those who have the most offspring that reproduce

• So, the answer to the trilogy of problems is:• ‘Descent with modification from a common ancestor,

NOT random modification, but, modification shaped by natural selection’

Different types of selection

• Directional Selection• What most of us think

about when we think about selection

• An extreme value is selected for

• Human brain size is a nice example

Different kinds of selection

• Stabilizing or Normalizing selection

• The middle is selected for

• Many examples here– Symmetry– Two eyes

Different kinds of selection

• Disruptive selection• Extremes are selected

for• Might be where the

two sexes come from• Trait was probably

gamete sized• Two ‘mating types’

Other Evolutionary Theories

• Lamarckism– Inheritance of acquired characteristics

• E.g., giraffes really wanted leaves, so they stretched their necks and…..

• Sounds crazy, but a lot of people think this way• ‘We will all have giant heads and tiny bodies someday’• ‘Cave swelling fish don’t use their eyes so they disappear’• ‘We don’t use our appendix so it is disappearing’

Silly incorrect evolutionary theories and ideas

• Orthogenesis– There is some plan to evolution. – NO WRONG INCORRECT, THANKS FOR PLAYING– The idea of an ‘evolutionary ladder’ fits in here– It is wrong too……

Still another silly idea

• Intelligent Design• Just Creationism with a fancy name• God does not belong in a science class, any

more than experiments belong in church• NOT A SCIENTIFIC THEORY