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

Ventilation of tracheal system, Ventilation of Tracheal System The man...

Ventilation of Tracheal System The manner in which tracheae are ventilated varies with species of insects but movement of air is achieved in two ways: Diffusion

What are the hormones secreted by the adrenal cortex, Q. What are the hormo...

Q. What are the hormones secreted by the adrenal cortex? What are their respective functions? The cortical portion of the adrenals secretes hormones of the corticoid (or cortic

Animal tissue, Animal Tissue A tissue is a group of cells that are si...

Animal Tissue A tissue is a group of cells that are similar in structure, origin and function. Tissue word coined by Bichat (Father of Histology). Histology term

Describe the general examination of clinical examination, Describe the gene...

Describe the general examination of clinical examination? It is always to better to ask the patient to help himself/herself in setting on to the examination table and rename so

Show the pre-diabetes conditions, Q. Show the Pre-Diabetes Conditions? ...

Q. Show the Pre-Diabetes Conditions? Pre-diabetes is a condition which may occur between normal and diabetes stages. It is important for you to know about this group of people,

What is intermittent treatment, Intermittent Treatment Intermittent 4...

Intermittent Treatment Intermittent 4-drug regimens with 2 or 3 doses per week after at least 2 weeks of daily therapy are also effective for treatment of TB and should alway

Mollusca, An account of characters of mollusca

An account of characters of mollusca

Blastomycosis, Blastomycosis Blastomyces dermatidis is a dimorphic fung...

Blastomycosis Blastomyces dermatidis is a dimorphic fungus existing as a mold in the soil (saprophytic stage) and as a yeast in tissues (parasitic stage). It causes systemic fu

Fats and lipids, Composed of C, H and O (fewer polar OH bonds than carbohyd...

Composed of C, H and O (fewer polar OH bonds than carbohydrates) Can be used at energy storage, components of cell membranes, chemical signals & thermal insulation Are

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