Darwin’s Tea PartyDarwin’s Tea PartyThe Theory of Evolution by Natural The Theory of Evolution by Natural SelectionSelection

Charles Darwin (1809-1882)Charles Darwin (1809-1882)

Last update 8 Oct, 2009

Biological Evolution

Definition: “Change in the genetic composition of a population during successive generations (due partly to natural selection) and resulting in the development of new species” (Wesbter’s).

Biological Evolution

The ancestors of the horse, for example, have undergone considerable change in physical size and proportions over the last 60 million years.

• The adult size, shape, bones, internal organs and many other physical and behavioural features have changed.

• The original Eohippus was thus a different “type of animal” (species) than the present day horse (Equus)

Biological Evolution

Evolution and Genes

Such changes in body parts are the result of changes in genes. When nature “selects” the “fittest” for survival and reproduction, it is also selecting the fittest combination of genes to survive and reproduce. These come “packaged” in a creature’s body.

Evolution and Genes• Thus Biological Evolution Thus Biological Evolution

happens through the happens through the transmission of genetic transmission of genetic characteristics from one characteristics from one generation to the next.generation to the next.

• Individuals who are the Individuals who are the most genetically “fit”, most genetically “fit”, survive to reproduce survive to reproduce (called natural selection (called natural selection or “survival of the or “survival of the fittest”) and pass on their fittest”) and pass on their fit characteristics.fit characteristics.

Evolution and Genes

• During Darwin’s time not much was known about genetics.

• But Darwin did know that variation existed.

• That was enough to establish that in every species only those individuals that had favourable variations would be more fit and thus live on and reproduce.

Evolution by Natural Selection

• Natural selection is not the Natural selection is not the same as evolutionsame as evolution

• Natural selection is one Natural selection is one cause of biological evolution.cause of biological evolution.

• It is like an “engine” that It is like an “engine” that drives evolution on. drives evolution on.

Evolution by Natural Selection• “Natural selection” is a metaphor

which Darwin compared to “artificial selection” (the breeding of plants & animals).

• In “artificial selection”, humans “select” which individual plant or animal will reproduce.

• In natural selection, “nature” does this “selecting”.

• In fact, Darwin begins his Origin by discussing the artificial selection (breeding) of pigeons.

• In this example, we can see how three radically different looking breeds of pigeon (Pouter, Jacobin and Fantail) have been produced by artificial selection from the original Wild Rock pigeon.

Natural & Artificial Selection

Natural & Artificial Selection

Varieties of bananas produced by artificial selection

Natural & Artificial Selection

Note how all these dramatically different vegetables were created by artificial selection from an original ancestor.

Natural Selection

How does it work?

Natural Selection is like a machine with 3 parts:

1. VariationThe tendency for individuals in a species to differ slightly from their parents and from each other.

2. Population Pressurethe tendency for population growth to outstrip available resources

3. Deep TimeThe discovery that the earth (and life on it) was far older than had previously been thought.

1. Variation

1. VariationThe tendency for individuals in a species to differ slightly from their parents and from each other.

1. Variation

Variation among high school students

Will this be on the test?

1. Variation

Variation within a family(not the dog – it’s a different species)

You mean I

was adopted

?

Variation between house cats (felis domesticus)

They think

were cute now

1. VariationBut wait till they see their couch

1. Variation

The exact causes of variation were discovered only after Darwin’s death. The discovery was made by the Austrian monk Gregor Mendel, the father of modern genetics. Gregor Mendel (1823-1884)

I love peas

1. Variation

• One cause of variation is sex - the combining of the genetic material of male and female to create offspring. (Also called sexual recombination)

• Another cause was mutation - accidents to the genetic material

• Variation is NOT caused by population increase or by the environment or by use/disuse, etc…

1. Variation

• Variation means there are different degrees of fitness among individuals in a population of the same species.

• Some happen to be born with advantageous variations (giving them added fitness) and others not.

2. Geometrical Population Increase

2. Geometrical Population IncreaseThe tendency for a population of any given species tends to outstrip the available resources necessary to keep it alive.

As Darwin says, “More are born than can possibly survive”.

2. Geometrical Population Increase

The “principle of population” was first expressed by the British political economist, Reverend Thomas Malthus.

Thomas Malthus (1766-1834)

Want less Want less poverty? STOP poverty? STOP

HAVING HAVING SEX!!!SEX!!!

2. Geometrical Population Increase

In the human world, Malthus said, population tends to increase at a “geometric” rate while resources increase only at an “arithmetic” rate. Population

Tim

e Population

Resources

Malthus’ Concept of Geometric Population Increase (GPI) in the

human world:

2. Geometrical Population Increase Given this geometric rate of increase, part of the human population is bound to be poor or even die.

As Malthus states, “...more will always be in want than can actually be supplied”.

2. Geometrical Population Increase

Darwin applied Malthus’ idea of geometric population increase to the entire living world.

He saw that it would lead to a “struggle for survival” continuously occurring between individuals in nature.

2. Geometrical Population Increase

This “struggle for survival” would leave only the “fittest” individuals to survive (those with favourable variations) and reproduce Thus: GPI + V = NS (natural selection also called “the survival of the fittest”).

• By “fit” Darwin meant not just the “strongest” but those best adapted to the environment

• These would tend to leave more offspring behind than the less fit.

2. Geometrical Population Increase

3. Deep Time

3. Deep TimeDeep time is the theory that the earth – and life on it – have been around for much, much longer than previously thought.

3. Deep Time

• Given sufficient time (deep time) natural selection will have “weeded out” so many unfavourable variations and accumulated so many favourable variations that a new species will have developed from a previous ancestor.

3. Deep Time

• Evolution by Natural Selection thus required millions of years to transform small changes into big ones.

• But many naturalists believed that the Earth was only about 6,000 years old.

3. Deep Time

The Irish Archbishop James Ussher (1581-1656) calculated the age of the earth according to what he believed the Bible indicated.

3. Deep Time• According to Ussher

the universe began on Sunday, 23 October 4004 BC at 9:00 AM.

• This was not enough time for evolution to have occurred

Archbishop James Ussher (1581-1656)

I’m a YEC!

3. Deep Time

Charles Lyell (1797-1875)Charles Lyell (1797-1875)

• But by the 19th century, the science of geology confirmed that the earth was actually millions of years old.

• Key was geologist Charles Lyell’s book Principles of Geology which Darwin had read on the Beagle.

Geology Rocks!

3. Deep Time

• Thanks to Lyell and the science of geology, the earth – and life on it – were proven to be much older than anyone previously thought

• For Darwin deep time was a key to acceptance of his evolutionary theory which required a huge time scale.

3. Deep Time: The Grand Canyon

6000 feet deep at its lowest and 15 miles across at its widest. 6000 feet deep at its lowest and 15 miles across at its widest.

The Colorado river has cut into the Canyon, exposing almost 2 The Colorado river has cut into the Canyon, exposing almost 2 billion years of earth’s history. billion years of earth’s history.

The Canyon’s geological structure shows it was made by a very, The Canyon’s geological structure shows it was made by a very, very long process of erosion by wind and water as well as very long process of erosion by wind and water as well as volcanic activity and other geological processes.volcanic activity and other geological processes.

3. Deep Time: The Grand Canyon

3. Deep Time3. Deep Time

This chart gives us some idea of the scale of deep time. Note how recent is the arrival of Homo.

3. Deep Time

• Another way of visualizing deep time

• Note the many periods of glaciation

• Note the changes in the shape and position of continents

Summary: Natural Selection• Geometrical Population Increase (GPI)

causes “struggle for survival” (meaning only some individuals will live and reproduce)

• Variation (V)causes differences in fitness b/w individualsTHUS:GPI + V = “survival of the fittest” (natural

selection)

Summary: NS + Deep Time

Natural Selection +

Deep Time =

Biological Evolution

Cast of charactersCharles Darwin (1809-1882)

Founder of theory of evolution by natural

selection Charles Lyell (1797-1875)

Discoverer of ‘deep time’

Thomas Malthus (1766-1834)Articulates the ‘principle of population’

Gregor Mendel (1823-1884)Founder of science of genetics

The End

Written & Directed by Gabriel Tordjman