Phenotypic variation is the variation which appears in the phenotype or morphology of the organism. Natural selection is the mechanism of evolution in which the adapated organism to the environment is selected or highly favoured during the course of evolution.
A phenotype is the results of the genetic change which to be established in a population has to be passed on to the generation.
Since variation in phenotypic traits allows the organism to leave indifferent circumstances therefore phenotypic variation proves essential condition to natural selection.
Convection occurs when particles with a lot of heat energy in a liquid or gas move and take the place of particles with less heat energy. Heat energy is transferred from hot places to cooler places by convection. Liquids and gases expand when they are heated. ... The denser cold liquid or gas falls into the warm areas.
The "Introduction" section of a research article contains the detailed background information on the topic and the problem that is being answered by the research.
Experimental design as well as materials and methods are mentioned in the "Materials and Methods" section of a research article.
