Industrial melanism, Biology

Assignment Help:

In this section, we shall discuss a classic example of natulal selection in action. In the preceding unit, it was stated that natural selection always aims at eliminating alleles, which are less adapted to the environment. Conversely selection indirectly aims to promote those alleles or individuals that are well adapted to a given environment.

The promotion and establishment of an allele and the resultant phenotype may take several hundreds of years in natural populations. But there are indeed instances where the selective forces have brought changes in the character of individuals within historical times.

The peppered moths Biston betillaria occur in two forms, the melanic and non-melanic. As shown in Fig. the melanic forms are black in colour and non-mel?nic ones are mottled grey. Until the early part of the 19th century, the melanic forms were regarded as rare and prize collections by insect collectors, and the light non-melanic forms were abundantly present in natural populations. The rarit.? of black forrns was essentially due to the higher rate of predation by birds. The black forms resting on light coloured and lichen encrusted trees were the easy targets for the birds. The light coloured non-melanics blend with their background, and therefore, are not easily visible to the predators. With the onset of the industrial revolution the distribution of melanic forms particularly in the industrial centres underwent a great change. An examination of museum collection of insects over the past 100 years showed that the melanic forms increased in numbers and the non-melanics were becoming rarer and rarer. What could be the possible reason for such an occurrence? In industrial regions, the sooty smoke emanating from factories blackened the bark of the trees and prevented the growth of lichens. This resulted in the black coloured forms resting on such trees becoming invisible to the p~edators and the light coloured ones being increasingly susceptible to the predator attack because of their contrast with the background. In industrial areas the birds predated upon non-melanics in extremely large numbers whereas in other areas melanics were preferentially caten. Since the proportion of melanics increased due to industrial activity, the examplc is often referred to as industrial melanism.


Related Discussions:- Industrial melanism

Nutrition, what is the mode of nutrition in tape worm

what is the mode of nutrition in tape worm

How is the large size of some cephalopods, How is the large size of some ce...

How is the large size of some cephalopods related to the type of circulatory system they present? In cephalopods the circulatory system is closed and this gives more speed and

Explain procedure for analysis of air of processing facility, Explain Proce...

Explain Procedure for Analysis of Air of Processing Facility? Now conduct the experiment following the steps enumerated herewith: 1. Label the Petri plates with nutrient aga

Methods of curing meat, M e t h ods of curing Curing ingredients ar...

M e t h ods of curing Curing ingredients are applied in dry form or as a solution of curing ingredients in water (pickle or brine). The combination cure is applied in the i

Fundamental polymers of life, The synthesis of the three fundamental polyme...

The synthesis of the three fundamental polymers of life, DNA, RNA and protein, is template-directed. This means that - Answer A. the monomers are assembled one by one in a sequence

Poultry and duck diseases-infectious laryngotracheitis (ilt), Infectious la...

Infectious laryngotracheitis (ILT) Infectious laryngotracheities, caused by fowl Gallid Herpesvirus 1 belonging to the family Herpesviridae, is a quickly spreading acute res

Define sugar as a type of carbohydrates, Define Sugar as a type of Carbohyd...

Define Sugar as a type of Carbohydrates? This group includes monosaccharide and disaccharides. List down the names of sugars under both these groups and check it out with those

Explain the periodic table of the elements, Explain the periodic table of t...

Explain the periodic table of the elements ? Periodic Table of the Elements :  An element is a pure substance composed of atoms all of a single kind. It cannot be broken down

How are genetic diseases classified, How are genetic diseases classified? ...

How are genetic diseases classified? The Genetic diseases classify into chromosomal abnormalities and genetic mutations. Between chromosomal abnormalities there are the aneu

Formula concentration and supplementation - calorie density, Define Formula...

Define Formula Concentration and Supplementation - Calorie Density? Formula Concentration can be done by decreasing the amount or water added in the mixing of the formula. Sta

Write Your Message!

Captcha
Free Assignment Quote

Assured A++ Grade

Get guaranteed satisfaction & time on delivery in every assignment order you paid with us! We ensure premium quality solution document along with free turntin report!

All rights reserved! Copyrights ©2019-2020 ExpertsMind IT Educational Pvt Ltd