5.1 Evidence for evolution (Selective Breeding (Breeding members of a…
5.1 Evidence for evolution
Populations of a species can gradually diverge into separate species via evolution
The degree of divergence between geographically separated populations will gradually increase the longer they are separated
As the genetic divergence between the related populations increase, their genetic compatibility consequently decreases
Eventually, the two populations will diverge to an extent where they can no longer interbreed if returned to a shared environment
When two populations can no longer interbreed and produce fertile, viable offspring they are considered to be separate species
The evolutionary process by which two related populations diverge into separate species is called speciation
Breeding members of a species with a desired trait causes the trait's frequency to become increasingly common in successive generations of the species.
Is a form of artificial selection where man intervenes in the breeding of species to produce desired traits in offspring.
This provides evidence of evolution as targeted breeds can show a significant amount of variation in a relatively short period of time.
Selective breeding of domesticated animals shows that artificial selection can cause evolution
Over the last 15000 years many breeds of dog have been developed by artificial selection from domesticated wolves
Similar structures are known as homologous structures
Evolution of Homologous structures by adaptive radiation (where several new species rapidly diversify from an ancestral source with each new species adapted to utilise the evolved structure in different ways)
Comparative anatomy of groups of organisms may show common structural features.
Classic example of a homologous structure would be the pentadactyl limb.
Amphibians, reptiles, birds and mammals are vertebrates with limbs
Despite their differences, the bone structure in all of them are very similar.
This structure is known as the paradactyl limb and is likely to have evolved from a common ancestor with pentadactyl limbs.
Occurs when heritable characteristics of a species change over long periods of time
Heritable characteristics are encoded for by genes and may be transferred between generations as alleles
Fossils: The preserved remains of any organism fro the remote past.
Fossil record provide direct evidence of ancestral forms of organisms that live today.
Fossil record is the complete set of all fossils (both discovered and undiscovered).
It shows that evolution of living organism have occurred over time
The sequence in which organisms are arranged in the fossil record depend on their complexity. Many sequences are known and they link together existing organisms with their most likely ancestors.
Example: horses, asses and zebras, members of genus Equus, are most closely related rhinoceroses and tapirs
Evidence from patterns of variation
Continuous variation across the geographical range of related populations matches the concept of gradual divergence
Within a population of any given species there will be genetic variation (i.e. variation which is inheritable)
Typically this variation will be continuous and follow a normal distribution curve as the rate of change is gradual and cumulative
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
The degree of divergence will depend on the extent of geographical separation and the amount of time since separation occurred
Distant populations that separated a longer period of time ago will show more variation (more divergence)
Populations located in close proximity that separated recently will show less variation (less divergence)
Continuous range in variation between populations provides evidence for the evolution of species and the origin of new species by evolution
Development of melanistic insects in polluted areas
Dark varieties of typically light-coloured insects are called melanistic
, the peppered moth
Widely used as an example of natural selection, as the melanistic variety became commoner in polluted industrial areas where it is better camouflaged than the pale peppered variety
Explanation of industrial melanism
*Biston betularia roost on the branches of trees during the day.
In an unpolluted areas, tree branches are covered in pale-coloured lichens and peppered moths are well camouflaged against them
Sulphur dioxide pollution kills lichens. Soot from coal burning blackens tree branches
In polluted areas, the melanic variety of
replaced the peppered variety over a relatively short time, but not in non-polluted areas