Natural SelectionNatural Selection

Or, how did we get here….Or, how did we get here….

Key concepts:

• Communicate scientific understandings using descriptions, explanations, and models

• Explain why variation within a population can enhance the chances for group survival

• Analyze how structural behavioral, and physiological adaptations within a population enable it to survive in a given environment

Key Vocabulary:

• Species• Population• Adaptation• Natural selection• Selective Breeding

Time out for vocabulary:

• Natural selection: the process by which individuals that are better adapted to their environment survive and reproduce more successfully than less well adapted individuals do

• Adaptation: a characteristic that improves an individual’s ability to survive and reproduce in a particular environment

• Species: a group of organisms that are closely related and can mate to produce fertile offspring

• Population: group of individuals of the same species in the same place

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

Parts:Parts:

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

Say that I, 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

Say that I, 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’

SOOOOOO…what does it mean…SOOOOOO…what does it mean… Evolution is a change over time in a

population of organisms…they have to reproduce in order to pass the traits…

Turn to page 115--Insects

Evolution is a change over time in a population of organisms…they have to reproduce in order to pass the traits…

Turn to page 115--Insects

Human intervention:Human intervention:

Dog breeds…how did we do it? Breed dogs of certain qualities with other

dogs with traits we wanted… Continued to do this and we get a dog that

we want.

Dog breeds…how did we do it? Breed dogs of certain qualities with other

dogs with traits we wanted… Continued to do this and we get a dog that

we want.

What does this mean:What does this mean:

Our traits will change over time in order to BETTER adapt to what is going on in our environment

This can lead to changes in species and even the making of a new species…

Our traits will change over time in order to BETTER adapt to what is going on in our environment

This can lead to changes in species and even the making of a new species…

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’

What does it all mean?What does it all mean?

Evolution is driven by NATURAL selection.

Evolution is driven by NATURAL selection.

What did your moth simulation tell you?

What did your moth simulation tell you?