5.1 Evidence for evolution

Question 1

When does evolution occur?

Answer 1

When heritable characteristics of a species change.
- Heritable characteristics are encoded by genes and may be transferred between generations as alleles (alternative forms of a gene)

Question 2

Define biological evolution

Answer 2

A change in the allele frequency of a population’s gene pool over successive generations.

Question 3

How can fossils be dated?

Answer 3

Fossils can be dated by determining the age of the rock layer (strata) in which the fossil is found.
Prokaryotes appear in the fossil record before eukaryotes
Ferns appear in the fossil record before flowering plants
Invertebrates appear in the fossil record before vertebrate species

This ordered succession of fossils suggests that newer species likely evolved as a result of changes to ancestral species

Law of fossil succession

Question 4

Evidence for evolution: fossils

Answer 4

• Fossils: like a casting or a mold for what was previously there
• Formed because there are trapped between minerals, starved from oxygen (so the bacteria can’t decompose it), which allows the biological material to be fossilized.

What is the evidence for evolution provided by fossils:
- Fossils show that over time changes have occurred in the features of living organisms (evolution)
- They can be used to indentify shared features with existing organisms to show common ancestry

Question 5

Transitional fossils

Answer 5

Fossils that show links between ancestral groups

Question 6

Selective breeding

Definition

Answer 6

A form of artificial selection, where humans intervene in the breeding of a species to produced their desired traits in offspring.
- By breeding members of a species with a desired trait, the trait’s frequency becomes more common in successive generations

Therefore, artificial selection can cause evolution.

Question 7

What are vestigial structures?

Answer 7

Body parts that have lost their use through evolution

Question 8

Example of selective breeding

Horse breeding

Answer 8

Horses have been selectively bred across many generations to produce variation according to a targeted function:
- Race horses have been bred for speed and hence are typically leaner, lighter, taller and quicker
- Draft horses have been bred for power and endurance and hence are sturdier and stockier

Question 9

What is comparative anatomy?

Answer 9

When groups of organisms show certain features that are similar (homologous structures), implying they have evolved from a common ancestor.

Question 10

Divergent evolution

Answer 10

When two separate species have a similar structure, but use it in different ways because of their environment.
- Homologous structures

Question 11

What are homologous structures?

Answer 11

• Anatomical features that are similar in basic structure despite being used in different ways
• The more similar the homologous structures between two species are, the more closely related they are likely to be

Question 12

What is adaptive radiation?

Answer 12

A process in which organisms rapidly diverge from the form of the original species into several new forms specialised to make use of different environmental niches.
- This is caused by divergent evolution

Question 13

Example of homologous structure: pendatactyl limb

Answer 13

• Mammals, birds, amphibians and reptiles all share a similar arrangement of bones in their appendages based on a five-digit limb
• Despite possessing similar bone arrangements, animal limbs may be highly dissimilar according to the mode of locomotion:
• Human hands are adapted for tool manipulation (power vs precision grip)
  Bird and bat wings are adapted for flying
  Horse hooves are adapted for galloping
  Whale and dolphin fins are adapted for swimming

Indicates common ancestry

Question 14

Convergent evolution

Answer 14

When organisms that are not closely related evolve similar structures that are used for similar purposes.
- This is often because their habitats or diets are similar.

Question 15

Analogous structure

Answer 15

Structures that are similar in structure, but have evolved separately (from different origins) are known as analogous structures.

Question 16

Example of analogous structure: fur in animals in Arctic ecosystems

Answer 16

Animals in Arctic ecosystems have white fur or feathers, this doesn’t mean they evolved from the same ancestor.

Question 17

Does continuous variation across a geographical range of related populations correspond to the concept of gradual divergence?

Answer 17

Yes!
- If two populations of a species become geographically separated then they will likely experience different ecological conditions
- Over time, the two populations will adapt to the different environmental conditions and gradually diverge from one another

Question 18

Speciation

Answer 18

• The process by which new species form
• Occurs when two populations (of the same species) diverge to an extent where they can no longer interbreed if returned to a shared environment

Question 19

Peppered moths

Example of evolution by natural selection

Answer 19

Peppered moths (Biston betularia) exist in two distinct polymorphic forms – a light colouration and a darker melanic variant
- In an unpolluted environment, the trees are covered by a pale-coloured lichen, which provides camouflage for the lighter moth
- In a polluted environment, sulphur dioxide kills the lichen while soot blackens the bark, providing camouflage for the dark moth

• Therefore, the frequency of the two different forms of peppered moth is dependent on the environment and evolves as conditions change
• Before the industrial revolution, the environment was largely unpolluted and the lighter moth had a survival advantage
• Following the industrial revolution, the environment became heavily polluted, conferring a survival advantage to the darker moth