EvolutionEvolution

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ContentsContents

DefinitionDarwin & WallaceNatural selection - the observationsNatural selection - the conclusions

Evidence to support evolution Anatomy Embryology Biochemistry Cytology Physiology

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EvolutionEvolution

is about how modern day plants and animals is about how modern day plants and animals have gradually developed from pre-existing have gradually developed from pre-existing forms, over long periods of time i.e. forms, over long periods of time i.e.

changes in species by natural selection in changes in species by natural selection in response to environmental changes i.e.response to environmental changes i.e.

survival of the fittest.survival of the fittest.

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Darwin & WallaceDarwin & Wallace

Many scientists had stated that species must Many scientists had stated that species must have evolved from one another.have evolved from one another.

Charles Darwin (1809 – 1882) – first to Charles Darwin (1809 – 1882) – first to suggest a mechanism or theory for it to suggest a mechanism or theory for it to happen – did not publish his theory.happen – did not publish his theory.

Sixteen years later Alfred Wallace came up Sixteen years later Alfred Wallace came up with the same theory.with the same theory.

The mechanism is called natural selection.The mechanism is called natural selection.Based on four observations and two Based on four observations and two

conclusions.conclusions.

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Natural selection – the Natural selection – the observationsobservations

1.1. Individual members of a species are Individual members of a species are different from one another.different from one another.

2.2. Offspring resemble their parents (variation Offspring resemble their parents (variation is inheritable).is inheritable).

3.3. More offspring are produced than can More offspring are produced than can survive and reproduce.survive and reproduce.

4.4. There is a struggle for existence and some There is a struggle for existence and some individuals have variations that make individuals have variations that make them better suited to survival than others.them better suited to survival than others.

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Natural selection – the Natural selection – the conclusionsconclusions

favourable variations may make individuals favourable variations may make individuals more adaptable more adaptable

– – these variations are passed on genetically these variations are passed on genetically and will eventually become the norm.and will eventually become the norm.

=> survival of fittest.=> survival of fittest. successive variations accumulate and successive variations accumulate and

eventually interbreeding between this and eventually interbreeding between this and the original organism is no longer possible.the original organism is no longer possible.

=>new species formed.=>new species formed.

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Evidence to support evolution Evidence to support evolution (1/2)(1/2)

The evidence shows that there was a common The evidence shows that there was a common descent between different groups of organisms descent between different groups of organisms

or that different organisms share a common or that different organisms share a common ancestor.ancestor.

The evidence comes from a number of sources: -The evidence comes from a number of sources: - Fossils – Palaeontology Fossils – Palaeontology Geographical distribution Geographical distribution Taxonomy andTaxonomy and

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Evidence to support evolution Evidence to support evolution (2/2)(2/2)

from the comparative studies of:from the comparative studies of:

- - Anatomy- Embryology- Embryology- Biochemistry- Biochemistry

- Cytology- Cytology- Physiology- Physiology

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Comparative anatomyComparative anatomy

The forelimbs of terrestrial vertebrates are The forelimbs of terrestrial vertebrates are similar in structuresimilar in structure

- the basic structure is known as the the basic structure is known as the

pentadactyl limb.pentadactyl limb. The forelimbs share the same basic structure The forelimbs share the same basic structure

but differ in their functions:but differ in their functions:

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Structures that differ in functionStructures that differ in function

human human - lifting and grasping- lifting and graspingrabbit rabbit - leaping- leapingwhale fin whale fin - swimming- swimmingant eater ant eater - tearing- tearingbat wing bat wing - flying- flyingmonkey monkey - grasping- graspingmole mole - digging- digginghorse horse - speed- speed

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The The pentadactyl pentadactyl

forelimb in a forelimb in a number of number of vertebratesvertebrates

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Vestigial structuresVestigial structures

Some structures have been lost Some structures have been lost – they no longer serve a – they no longer serve a function. function.

e.g. horse stands on its third e.g. horse stands on its third toe. toe.

Toes two and four are present Toes two and four are present in a vestigial form. One and in a vestigial form. One and five are no longer present.five are no longer present.

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Comparative embryologyComparative embryology

The study of developing embryos of The study of developing embryos of vertebrates shows a similarity between vertebrates shows a similarity between certain structures certain structures

e.g. the position of the brain, eyes, e.g. the position of the brain, eyes, gill slitsgill slits and tail of the fish, tortoise, rabbit, bird, and tail of the fish, tortoise, rabbit, bird, chick and human. chick and human.

This suggests that organisms descended from This suggests that organisms descended from common ancestors.common ancestors.

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e.g. gill slitse.g. gill slits

If all vertebrates came from a common If all vertebrates came from a common ancestor who had gills, ancestor who had gills,

it would be likely that all vertebrates would it would be likely that all vertebrates would develop gills develop gills

and then modify them into other structures. and then modify them into other structures. This is exactly what happens.This is exactly what happens.

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A comparison of four A comparison of four vertebrate embryosvertebrate embryos

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Comparative biochemistryComparative biochemistry

The similarities between the respiratory The similarities between the respiratory pathways in all living cells suggest a pathways in all living cells suggest a common ancestor.common ancestor.

All living things use DNA, ATP and many of All living things use DNA, ATP and many of their protein structures are very similar.their protein structures are very similar.

The greater the similarity in protein The greater the similarity in protein structures, the more closely related they are, structures, the more closely related they are,

and the smaller will be the difference in their and the smaller will be the difference in their DNA structure.DNA structure.

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An An evolutionary evolutionary

tree based tree based on on

similarities similarities in fibrinogen in fibrinogen

moleculesmolecules

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Comparative cytologyComparative cytology

The presence of organelles such as The presence of organelles such as mitochondria, endoplasmic reticulum and mitochondria, endoplasmic reticulum and ribosomes in most cells and substances such ribosomes in most cells and substances such as DNA, RNA and ATP suggests a as DNA, RNA and ATP suggests a common ancestor.common ancestor.

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Comparative physiologyComparative physiology

A study of the similarities between blood A study of the similarities between blood pigments in the animal kingdom suggests a pigments in the animal kingdom suggests a common ancestor.common ancestor.

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ENDENDGo to PPT on ‘The Evidence for Evolution’

Contains some very good pictures