A4.1 Evidence for Evolution

1. DNA, RNA, and Protein Structures

2. Homologous Structures

3. Selective Breeding

1. Bio-molecules 
   
   • Provide strong evidence
   • Same genes present in organisms that evolved from a common ancestor
   • Differences in DNA sequences are the result of mutation
   • Mutation accumulates gradually over long periods at a constant rate. 
   • Closely related species have very similar gene and protein sequences, due to a small number of mutations because they diverged from a common ancestor. 
2. Homologous structures 
   • Similar in structure but may have different functions.
   • Evolved from a common ancestor
   • Populations evolved to fit/adapt to their environment, resulting in modified homologous structures adapted to survive in the new environment. 
   • Example: Pentadactyl limb structures- evolved from a common ancestor; they are greatly modified for a variety of purposes.
3. Selective Breeding
   • Process of humans choosing plants or animals with desirable traits to breed together and produce offspring with the desirable traits. 
   • Example - Interbreeding of dogs
   • The selective breeding of crops (agriculture) demonstrates how rapidly evolution can occur. 

Evolution occurs when the heritable characteristics of species change.

- the process of cumulative change (small changes accumulate to big changes) in the heritable characteristics of a population. 

- heritable characteristics of a species changes due to changes in allele frequencies.

*individuals cannot evolve, populations evolve.

Populations of a species can gradually diverge into separate species by evolution.

- populations gradually diverge into seperate species with reproductive isolation via natural selection as different selection pressures are applied on different species

- populations can also gradually diverge from different geographic ranges ( continuous variation )

Continuous variation across the geographical range of related populations matches the concept of gradual divergence

Evidence for evolution:

• The fossil record provides evidence for evolution.

• homologous structures = Anatomical features that are similar in basic structure despite being used in different ways
• selective breeding of domesticated animals ( eg dogs )
• patterns of variation

Fossil record shows:

• how long life has been around using radioisotope dating
• simple bacteria to more complex life forms
• intermediates between ancestral groups

Evolution of homologous structures by adaptive radiation explains similarities in structure when there are differences in function.

Adaptive radiation = type of divergence where species rapidly diverge into many different species as different populations specialise in different niches

- homologous strcutures is evidence that organisms had a common ancestor then evolved to suit different functions

Selective breeding of domesticated animals shows that artificial selection can cause evolution.

Selective breeding is a form of artificial selection, whereby man intervenes in the breeding of species to produce desired traits in offspring

• By breeding members of a species with a desired trait, the trait’s frequency becomes more common in successive generations
• Selective breeding provides evidence of evolution as targeted breeds can show significant variation in a (relatively) short period

Selective breeding examples:

• Plants of the genus Brassica have been bred to produce different foods by modifying plant sections through artificial selection
• This includes broccoli (modified flower buds), cabbage (modified leaf buds) and kale (modified leaves)
• Domesticated animals can be seen in horse, cows and dogs

Development of melanistic insects in polluted areas.

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

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
• Recent environmental policies in Europe are reducing pollution levels, altering the frequency of the two populations once again

Comparison of the pentadactyl limb of mammals, birds, amphibians, and reptiles with different methods of locomotion.

A classical example of homologous structures is the pentadactyl limb in a variety of different animals

• 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

5.2 Natural Selection

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