Evolution

Homologous structures have the same embryonic origin and basic structure, but they do not perform same function, e.g. flipper of whale and wings of bat.

Analogous organs are the structures which are different in their basic structure and developmental origin, e.g. wings of butterfly and wings of bird.

Industrial melanism is an adaptation where the moths living in the industrial areas developed melanin pigments to match their body to the black soot (smoke) covered surroundings. The peppered moths exist into two strains– light (white) coloured and melanic (black). Before industrialisation, all moths were white and were unnotied from predatory birds due to whitish lichens on the bark of trees. After industrialisation, the barks get covered by smoke so the white moths were more evidently visible and thus, picked up by birds. But black moths escaped unnoticed so they managed to survive resulting in more population of black moths and less population of white moths.

Change in population density gives an idea of what is happening to the population, whether it is increasing or declining. This population density depends on natality, mortality, immigration and emigration. In an isolated small tribal population, if boys marry their own tribal girls then there will be decline in population because at some stage marriage will stop due to isolation and on the other hand marriages within same tribe will lead to homozygosity of disease and ultimately death, thus leading to decline in population.