EXAMPLES used to support Darwin's theory

Some examples Charles Darwin used to support his theory are the finches as well as the peppered moths.

DARWIN'S FINCHES

Scientific Classification
Kingdom: Animalia
Phylum: Chordata
Class: Aves
Order: Passeriformes
Family: Emberizidae

Darwin's finches (also known as the Galápagos Finches) are 13 or 14 different but closely related species of finches Charles Darwin collected on the Galapagos Island. The group consists of ground-dwelling birds (Geospiza) that feed on different sized seeds or cactus flowers as well as tree-dwelling birds (Camarynchus) that feed on different types of insects or types of fruit. The beaks belonging to each type or finch are adapted for a specialized feeding task. Thirteen of the finches reside on the Galápagos Islands and one on Cocos Island.

All the species of finches on the Galápagos Islands appear morphologically very alike, varying mostly in terms of beak size and behaviour. All of them appear very much like a type of finch which can be found in the mainland of South America. This insinuates that all the finches on the Galápagos Island descended from one original colonist species that adapted to a variety of feeding conditions went. Also, this seems to show that when different populations of species become reproductively isolated from one another by adapting to differing ecological niches, they ultimately become distinct and individual species. This process is as adaptive radiation whereby one species diversifies into several other species in order to utilize the extensive range of habitats.

This diagram shows the relationship between the diet of the birds, the purpose of the beaks, the usual location of the birds as well as the shape and size of the beaks

This diagram shows the types of beaks in relation to its purpose

1) Source: http://en.wikipedia.org/wiki/Darwin's_finches, 14th April 2007
2) Source: http://www.ncseweb.org/icons/icon7finches.html, 7th April 2007

3) Source [2nd picture & some info]: http://www.hras.org/sw/sw11-04.html, 17th April 2007

4) Source: http://anthro.palomar.edu/evolve/evolve_2.htm, 17th April 2007

5) Source [1st picture]: http://www.pbs.org/wgbh/evolution/library/01/6/l_016_02.html, 7th April 2007

PEPPERED MOTHS- Biston betularia

Scientific classification
Kingdom: Animalia
Phylum: Arthropoda
Class: Insecta
Order: Lepidoptera
Family: Geometridae
Genus: Biston
Species: B. betularia

Evidence for selection over a much shorter time, from 1848 onwards, comes from looking at the population of the peppered moth. There are two different kinds of moths, dark and light coloured. The colour of the moth offers camouflage against the tree barks, as can be seen from the photographs below.

Moths with light-colouration are well camouflaged against lichen-covered bark, but moths with dark-colouration are more noticeable against that background are hence are more likely to be spotted by predators and be eaten up. However, when soot increasingly caused the lichens to die out and the trunks of the trees to turn black in industrial areas during the Industrial Revolution in England, the dark moths, or melanic moths- carbonaria, were able to camouflage themselves better and as a result they usually live long enough to reproduce. On the other hand, the light-coloured moths, or typica, died off due to predation. Over generations, the environment continued to favor darker moths. Thus, they gradually became more common in comparison to light coloured moths. 98% of the moths in the vicinity of English cities like Manchester were largely black by the 1895.

Biston betularia f. typica, the white-bodied peppered moth.

Biston betularia f. carbonaria, the black-bodied peppered moth.

Since the 1950's, air pollution was drastically reduced and hence, the lichen grew back, making the colour of trees lighter. Additionally, the once blackened buildings were cleaned making them lighter in color. Presently, natural selection favors lighter moth varieties so they have become the most common.

With the dramatic variation in the peppered moth’s population, it has continued to be an issue of much interest and study and has led to coining of the phrase “industrial melanism” which refers to the genetic darkening of species in response to pollutants.

1) Source: S Gater & V Wood-Robinson, "G.C.S.E Science Double Award-Biology", 1996, p. 158-159
2) Source: http://anthro.palomar.edu/evolve/evolve_2.htm, 17th April 2007

3) Source: http://en.wikipedia.org/wiki/Peppered_moth, 19th April 2007

chan li ying [evolution expert]