Natural SelectionNatural Selection

Or, how did we get here….

(Courtesy of Dr. David R. Brodbeck, Department of Psychology, Algoma University)

Or, how did we get here….

(Courtesy of Dr. David R. Brodbeck, Department of Psychology, Algoma University)

Natural SelectionNatural 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

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 FirstProblem 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.

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 ProblemThe 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

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 ProblemThe 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.

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!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.

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?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’

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?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

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?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

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…..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’

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 selectionDifferent 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

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 selectionDifferent kinds of selection Stabilizing or

Normalizing selection

The middle is selected for

Many examples here Symmetry Two eyes

Stabilizing or Normalizing selection

The middle is selected for

Many examples here Symmetry Two eyes

Different kinds of selectionDifferent 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’

Disruptive selection Extremes are

selected for Might be where the

two sexes come from

Trait was probably gamete sized

Two ‘mating types’

Other Evolutionary TheoriesOther 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 dwelling fish don’t use their eyes so they

disappear’ ‘We don’t use our appendix so it is disappearing’

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 dwelling fish don’t use their eyes so they

disappear’ ‘We don’t use our appendix so it is disappearing’