Speciation

BTEOTSSSBAT define speciation

Describe the evidence for evolution

Explain how speciation relates to natural selection

Evolution in actionwhat evidence is there to support the theory of

evolution?

All

Most

Some

• Can you define the term “speciation”?

• Can you describe the evidence for evolution

in action?

• Can you explain evidence to

evolution in action in terms of natural

selection?

STARTER QUESTION

What is ‘natural selection’?

Summary

Changes in the environment of plants and animals may

cause them to die out. The fossil record shows that new

organisms arise, flourish, and after a time become

extinct. The record also shows changes that lead to the

formation of new species.

Key words

Species

Fossils

Organisms

Decay

Extinction

Predators

Speciation

Isolation

Genetic variation

Natural selection

Geographical isolation

Endemic

Evolution

doesn’t

mean we

are

evolved

from

monkeys

Evolution

doesn’t

mean we

are

evolved

from

monkeys

B2.8.1 Old and new species

• The first organisms were very simple single-celled organisms,

similar to bacteria.

• However, these rarely survive as fossils.

• Therefore, scientists cannot be certain about how life

began on Earth.

• It is only possible to develop theoretical models that

show how life may have started.

a) Evidence for early forms of life comes from fossils.

b) Fossils are the ‘remains’ of organisms from many years ago,

and are found in rocks.

■ from the hard parts of animals that do not decay

easily

■ from parts of organisms that have not decayed

because one or more of the conditions needed for

decay are absent

■ when parts of the organism are replaced by other

materials as they decay

■ as preserved traces of organisms, eg footprints,

burrows and rootlet traces.

Fossils may be formed in various ways:

c) Many early forms of life were soft-bodied, which means

that they have left few traces behind. What traces there

were have been mainly destroyed by geological activity.

d) We can learn from fossils how much or how little

organisms have changed as life developed on Earth.

■ changes to the environment over geological time

e) Extinction may be caused by:

■ new predators may arise

■ new diseases may arise

■ new, more successful, competitors may arise

■ a single catastrophic event, eg massive volcanic

eruptions or collisions with asteroids

■ through the cyclical nature of speciation.

• If the organisms cannot evolve quick enough

to become better adapted to the change they

may become extinct.

• If they do evolve, they are likely to develop

into new species.

Complete the sentences using the words below:animal evidence fossils minerals plant

One important piece of …………. for how life has developed

on earth are …………… .

The most common type are formed when parts of the

……………. or …………..are replaced by ……….. as it

decays

A species is defined as a group of organisms that

are capable of breeding together to produce fertile

offspring.

What is a species?

A species is defined as a group of organisms that

are capable of breeding together to produce fertile

offspring.

What is a species?

Is a liger a

species?

What is ‘natural selection’?• Natural selection is the process whereby

organisms better adapted to their

environment tend to survive and produce

more offspring.

• The theory of its action was first fully

expounded by Charles Darwin and is now

believed to be the main process that

brings about evolution.

Natural selection can result in

the formation of new species…

• The formation of new species is know as

‘speciation’.

• Speciation can occur in a number of

ways…

This is evidence

for natural

selection in

action!

Formation of new species

The African and Asian elephants are

two separate but very closely related

species.

Formation of new speciesThis speciation has arisen due to

geographical isolation:

• A single population has become

separated into two groups.

A geographical (land)

barrier has stopped

them being all together

in one group.

Formation of new speciesThis speciation has arisen due to

geographical isolation:

• A single population has become

separated into two groups.

• Over time, each population of the

separate group evolves

differently due to genetic

variation.

Formation of new speciesThis speciation has arisen due to

geographical isolation:

• A single population has become

separated into two groups.

• Over time, each population of

the separate group evolves

differently due to genetic

variation.

• The longer they are separated,

the more different they become.

Formation of new speciesThis speciation has arisen due to

geographical isolation:

• A single population has become

separated into two groups.

• Over time, each population of the

separate group evolves differently

due to genetic variation.

• The longer they are separated,

the more different they become.

• Eventually, the two sub-

populations have changed so

much they can no longer

interbreed.

Formation of new speciesThis speciation has arisen due to

geographical isolation:

• A single population has become

separated into two groups.

• Over time, each population of the

separate group evolves differently

due to genetic variation.

• The longer they are separated, the

more different they become.

• Eventually, the two sub-populations

have changed so much they can no

longer interbreed.

• They have formed separate but

closely related species (speciation).

Natural selection in action:

The peppered moth

• The peppered moth

is native to the UK.

• It exists in one of two

forms:

– Light

– Dark

The Peppered Moth

• Before the 1800s, the

light moth was well

camouflaged against the

light bark of birch trees.

The Peppered Moth

• However, during the 1800s the industrial revolution occurred.

• All of the trees in industrial areas become darkened with soot from factories.

• The moths were no longer camouflaged….

The Peppered Moth

• A mutation occurred in

some moths, and their

colour was much darker.

• The darker moths now

had the advantage of

camouflage.

The Peppered Moth

• Over the next 50 years,

the dark variety become

more common.

• What do you think the

distribution of light and

dark moths is these

days?

The Peppered Moth

• Today, in cleaner areas

the light form of the moth

is more common again.

• In industrial areas, the

dark form is still the more

common form.

To Do:

• Peppered moth exam

questions.

• Work in pairs to

answer the exam

questions 1 &2 on pp.

5 and 7.

Self-Assessment

Self-Assessment

Self-Assessment

Self-Assessment

Self-Assessment