EVOLUTION:WHERE'S THE EVIDENCE?

Examples of evidence from:• The fossil record• Living populations• The DNA record

www.christs.cam.ac.uk/darwin200

EVIDENCE & EVOLUTION

What’s the evidence that evolution by natural selection happens?

There’s lots! Too much to catalogue here…

But we can discuss the sorts of evidence scientists have.

Evidence supporting natural selection comes from many sources, including:• the fossil record• observations of living populations• the DNA record

EVIDENCE & EVOLUTION

THE FOSSIL RECORD

Its very difficult to become a fossil

EVIDENCE & EVOLUTION

THE FOSSIL RECORD

Its very difficult to become a fossil

EVIDENCE & EVOLUTION

THE FOSSIL RECORD

Its very difficult to become a fossil

EVIDENCE & EVOLUTION

THE FOSSIL RECORD

Its very difficult to become a fossil

EVIDENCE & EVOLUTION

THE FOSSIL RECORD

Its very difficult to become a fossil

EVIDENCE & EVOLUTION

THE FOSSIL RECORD

Its very difficult to become a fossil

EVIDENCE & EVOLUTION

THE FOSSIL RECORD

Its very difficult to become a fossil

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EVIDENCE & EVOLUTION

THE FOSSIL RECORD

Its very difficult to become a fossil

Despite this the fossil record provides lots of evidence for evolution:• the earliest fossils appear in rocks 1-2 billion years old• the earliest fossil animals appear in rocks about 650 million years old• the fossil record contains many examples of intermediates between groups

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TRANSITIONAL FOSSILS: example 1 – from fish to tetrapods

Tetrapods share ancestry with lobe-finned fish.

EVIDENCE & EVOLUTION

coelocanth

salamander

TRANSITIONAL FOSSILS: example 1 – from fish to tetrapods

Tetrapods share ancestry with lobe-finned fish.

EVIDENCE & EVOLUTION

coelocanth

salamander

Acanthostega

TRANSITIONAL FOSSILS: example 1 – from fish to tetrapods

Tetrapods share ancestry with lobe-finned fish.

EVIDENCE & EVOLUTION

coelocanth

salamander

Tiktaalik

Acanthostega

TRANSITIONAL FOSSILS: example 1 – from fish to tetrapods

Tetrapods share ancestry with lobe-finned fish.

EVIDENCE & EVOLUTION

coelocanth

salamander

Tiktaalik

Ichthyostega

Acanthostega

EVIDENCE & EVOLUTION

TRANSITIONAL FOSSILS: example 1 – from dinosaurs to birds

Birds are living descendents of dinosaurs.

Coelophysis

EVIDENCE & EVOLUTION

TRANSITIONAL FOSSILS: example 1 – from dinosaurs to birds

Birds are living descendents of dinosaurs.

Coelophysis

Archeopteryx

EVIDENCE & EVOLUTION

TRANSITIONAL FOSSILS: example 1 – from dinosaurs to birds

Birds are living descendents of dinosaurs.

Coelophysis

Archeopteryx

Caudipteryx

EVIDENCE & EVOLUTION

TRANSITIONAL FOSSILS: example 1 – from dinosaurs to birds

Birds are living descendents of dinosaurs.

Coelophysis

Archeopteryx

Caudipteryx

Confuciusornis

EVIDENCE & EVOLUTION

LIVING POPULATIONS

Evolution is often thought to be very slow, too slow to observe within a human lifetime.

This isn’t true! We have a number of examples of evolution caught in action.

EVIDENCE & EVOLUTION

LIVING POPULATIONS

Evolution is often thought to be very slow, too slow to observe within a human lifetime.

This isn’t true! We have a number of examples of evolution caught in action.

MICROEVOLUTION

Microevolution is evolutionary changes within a population. - changes in allele frequencies- often has a small but significant phenotypic effect

Over many generations microevolution can ‘sum up’ to produce large changes.- it is the engine of evolution!

EVIDENCE & EVOLUTION

MICROEVOLUTION: example 1 – Darwin’s finches

The Galapagos Islands are home to 13 species of finches.

They are more closely related to each other than to any other species.

They are descended from a finch species that migrated to the islands from South America.

EVIDENCE & EVOLUTION

MICROEVOLUTION: example 1 – Darwin’s finches

The Galapagos Islands are home to 13 species of finches.

They are more closely related to each other than to any other species.

They are descended from a finch species that migrated to the islands from South America.

Since arriving on the island the finches have:- Specialised- Diverged

They now occupy different niches, each species feeding in a different way.

EVIDENCE & EVOLUTION

MICROEVOLUTION: example 1 – Darwin’s finches

Scientists have been studying the ground finches on one island called Daphne for 40 years.

There are 3 ground finches: a large, medium and small specieswhich specialise on large, medium and small seeds.with different sized beaks to match – big seeds need big beaks to crack open

EVIDENCE & EVOLUTION

MICROEVOLUTION: example 1 – Darwin’s finches

Scientists have been studying the ground finches on one island called Daphne for 40 years.

There are 3 ground finches: a large, medium and small specieswhich specialise on large, medium and small seeds.with different sized beaks to match – big seeds need big beaks to crack open

The researchers observed the finches during a drought:• plants struggled with water shortage• they produced fewer seeds

• the finches quickly ate all the small seeds• only large, tough seeds were left

• only the birds with the largest beaks could find food• the smaller-beaked birds starved

EVIDENCE & EVOLUTION

MICROEVOLUTION: example 1 – Darwin’s finches

Scientists have been studying the ground finches on one island called Daphne for 40 years.

There are 3 ground finches: a large, medium and small specieswhich specialise on large, medium and small seeds.with different sized beaks to match – big seeds need big beaks to crack open

The researchers observed the finches during a drought:• plants struggled with water shortage• they produced fewer seeds

• the finches quickly ate all the small seeds• only large, tough seeds were left

• only the birds with the largest beaks could find food• the smaller-beaked birds starved

the average beak size of the large ground finch increased by 1mm in one season – >10% increase!

EVIDENCE & EVOLUTION

MICROEVOLUTION: example 1 – melanism in peppered moths

Melanism is the occurrence of both a dark and light form of a species.

The peppered moth is a famous example.

The peppered moth (Biston betularia) has a few forms, one is:- typica - speckled white- carbonaria – black

They are found in woods in Britain, they are active at night and predated on by birds during the day when they are at rest on branches.

During the industrial revolution soot covered the lichen on tree trunks, the typica form was more easy for birds to spot & the carbonaria arose and increased in frequency.By 1895, 98% of Mancunian population were black.

EVIDENCE & EVOLUTIONMICROEVOLUTION: example 1 – melanism in peppered moths

A biologist called Kettlewell performed experiments to show that birds ate more typica than carbonaria in the 1950s.

The Clean Air Act was introduced in the 1950s, trees regained their former appearance. The typical form 6% to 30% by 1984 and continues to increase.

EVIDENCE & EVOLUTIONMICROEVOLUTION: example 1 – melanism in peppered moths

A biologist called Kettlewell performed experiments to show that birds ate more typica than carbonaria in the 1950s.

The Clean Air Act was introduced in the 1950s, trees regained their former appearance. The typical form 6% to 30% by 1984 and continues to increase.

This became a text book case of evolution in action.

However anti-evolutionists attacked the evidence.

Mike Majerus at Cambridge University responded by re-doing Kettlewell’s experiments – his hypothesis was that Carbonaria would decrease in frequency.

carbonaria

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2001 2002 2003 2004 2005 2006 2007

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EVIDENCE & EVOLUTIONMICROEVOLUTION: example 1 – melanism in peppered moths

A biologist called Kettlewell performed experiments to show that birds ate more typica than carbonaria in the 1950s.

The Clean Air Act was introduced in the 1950s, trees regained their former appearance. The typical form 6% to 30% by 1984 and continues to increase.

This became a text book case of evolution in action.

However anti-evolutionists attacked the evidence.

Mike Majerus at Cambridge University responded by re-doing Kettlewell’s experiments – his hypothesis was that Carbonaria would decrease in frequency.

carbonaria

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

2001 2002 2003 2004 2005 2006 2007

Year

Series1

That’s what he found! He tested each claim made by the critics and found no support for any of them: melanism in the peppered moth was confirmed as an example of microevolution

EVIDENCE & EVOLUTION

DNA

DNA is a molecule that carries instructions on how to build an organism.

It encodes information to build and express proteins:

DNA

messenger RNA

Protein

It is passed on from parent to offspring.Mutations in an organism’s DNA produce phenotypic changes – which natural selection then works one

EVIDENCE & EVOLUTION

THE DNA RECORD

All living organisms use DNA as their genetic information. As it is passed through generations the DNA sequence evolves.

We can sequence homologous stretches of DNA from different species and use them to test for relatedness.

EVIDENCE & EVOLUTION

THE DNA RECORD

All living organisms use DNA as their genetic information. As it is passed through generations the DNA sequence evolves.

We can sequence homologous stretches of DNA from different species and use them to test for relatedness.

We can also see that these same stretches of DNA often have conserved functions.

For example the HOX genes control the development of the body axis in animals.

HOX gene expression in mice.. … and humans

EVIDENCE & EVOLUTION

THE DNA RECORD

All living organisms use DNA as their genetic information. As it is passed through generations the DNA sequence evolves.

We can sequence homologous stretches of DNA from different species and use them to test for relatedness.

We can also see that these same stretches of DNA often have conserved functions.

For example the HOX genes control the development of the body axis in animals.

HOX gene expression in mice.. … and humans

DNA evolves through common descent& is acted upon by natural selection

EVIDENCE & EVOLUTION

THE DNA RECORD

Changes in DNA cause changes in development –acted upon by natural selection

For example: three-spine sticklebacks

EVIDENCE & EVOLUTION

THE DNA RECORD

Changes in DNA cause changes in development –acted upon by natural selection

For example: three-spine sticklebacks

Mutations in the gene Pitx1 affect the development of pelvic spines.

Pelvic spines are a defence against predation by fish.

Loss of the spines are thought to help the fish escape crustacean predators living on the water bed.

CONCLUSIONS: THE EVIDENCE FOR EVOLUTION

-Evidence from the fossil record

- Evidence from living populations

- Evidence from the DNA record

- Heritable changes in DNA affecting development fitness

www.christs.cam.ac.uk/darwin200

EVIDENCE & EVOLUTION

For more information on these examples and for more examples visit:

CONCLUSIONS: THE EVIDENCE FOR EVOLUTION

-Evidence from the fossil record

- Evidence from living populations

- Evidence from the DNA record

- Heritable changes in DNA affecting development fitness

www.christs.cam.ac.uk/darwin200

EVIDENCE & EVOLUTION

For more information on these examples and for more examples visit:

CONCLUSIONS: THE EVIDENCE FOR EVOLUTION

-Evidence from the fossil record

- Evidence from living populations

- Evidence from the DNA record

- Heritable changes in DNA affecting development fitness

www.christs.cam.ac.uk/darwin200

EVIDENCE & EVOLUTION

For more information on these examples and for more examples visit:

CONCLUSIONS: THE EVIDENCE FOR EVOLUTION

-Evidence from the fossil record

- Evidence from living populations

- Evidence from the DNA record

- Heritable changes in DNA affecting development fitness

www.christs.cam.ac.uk/darwin200

EVIDENCE & EVOLUTION

For more information on these examples and for more examples visit:

CONCLUSIONS: THE EVIDENCE FOR EVOLUTION

-Evidence from the fossil record

- Evidence from living populations

- Evidence from the DNA record

- Heritable changes in DNA affecting development fitness

www.christs.cam.ac.uk/darwin200

EVIDENCE & EVOLUTION

For more information on these examples and for more examples visit: