EXAMPLES OF NATURAL SELECTION -
1. INDUSTRIAL MELANISM -
- First studied by Fischer & Ford (1845) on pepperd moth (Biston betularia) of two types : grey moth (B. betularia betularia) and black moth (B. betularia carbonaria); the black moth population in Britain in (1845) was 1% which by 1895 came to 99%, it was thought that due to industrial pollution the grey moth changed into black. When coal run industries were replaced by electric / petroleum run industries the number of grey moths again increased (also correlated as reverse evolution) as pollution did not eliminate the gene of grey color.
- As explained by Neo-Darwinians both populations (grey & black) existed together, the environment favoured the one and disfavoured the other at different times resulting into their changed frequency.
- Bernard Kettlewell (1950) tested this by releasing equal numbers of grey and black moths in both polluted (Birmingham) and unpolluted (Dorset) areas. Later he captured 19% grey and 40% black moths from polluted areas and 12.5% grey and 6% black from unpolluted areas. This indicates the patterns of differential survival of the moths in respectively areas.
2. SICKLE CELL ANAEMIA -
- It is a genetic disorder caused by a single base substitution in a gene.
- The mutated gene changes the normal haemoglobin (HbA) to defective haemoglobin (HbS) and also makes the red blood corpuscles sickle shaped.
- The persons homozygous for the defective haemoglobin (HbS, HbS) die at an early age. In the heterozygous (HbA, HbS) the cell containing abnormal haemoglobin become sickle-shaped, and unable to bind oxygen efficiently.
3. BIO-INDICATOR PLANTS & ANIMALS -
- Plants which are specialized to grow under specific habitual conditions so that their presence in an area can indicate the same.
- Prosopis eineraria. P. dilensis, Acacai glandulosa. -Underground water
- Impatiens balsamina - Zinc (Zwar zinc mines, Udaipur)
- Haplopappus and Astragulus species - Selenium tolerant plant from U.S.A.
- Agrostis tenuis - On tailing of lead mines in wales, U.K. the variety from normal pasture couldn't survive on Pb-rich soil.
- Tubifix (Animal) - Pollution in water.