5.1 Evidence for Evolution

Question 1

Evolution

Answer 1

Evolution is the cumulative change in the heritable characteristics of a population (i.e. biological change over time)
- These characteristics are encoded by genes and transferred by generations of alleles.
Hence, evolution is a change in the alleles in the frequency of a population’s gene pool over Successive Generations

Question 2

Theories of Evolution: Lamarck

Answer 2

Proposed that species change via habitual use and disuse.
- A giraffe’s stretched it neck to leaves in tall trees.
-The giraffe’s neck becomes extended from constant use
-The giraffe’s offspring inherit its long
The theory has been rejected because these acquired traits do not have a genetic basis (and thus cannot be inherited)

Question 3

Theories of Evolution: Darwin (and Wallace)

Answer 3

Proposed that species change via natural selection
- A giraffe with longer neck can reach leaves in tall trees
- The giraffe will get enough food to survive and reproduce
- The giraffe has more offspring (that inherit a long neck)
Darwin’s theory has been reinforced by our understanding of modern genetics (incorporated as neo-Darwinism)

Question 4

what causes Mechanisms of Change

Answer 4

Fundamental to process evolution is the presence of variation within upon which selective forces act.
There are three main mechanism by which genetic variation within a population is maintained:
- Mutations - changes to gene sequence
- Sexual reproduction - new gene combinations
- Gene flow - immigration and emigration

Question 5

Mechanisms of Change

Answer 5

There are two mechanisms by population variety can be altered (down biodiversity)
- Random chance 9genetic drift)
- Directed intervention (natural or artificial selection)
The impact of a change is greater is the population is small (this may occur via population bottlenecks or founder effect)

Question 6

Speciation

Answer 6

If populations isolated, the level of genetic divergence gradually increases the longer the populations remain separated.
- Continuous variation across a geographical range of related population matched this concept of gradual divergence.
Speciation will occur when populations diverge to the extent that they can no longer interbreed and produce fertile, viable offspring