These term are used to classify organisms according to their evolutionary history. Simple organisms refer to those organisms that have simple structural and functional organisation and are considered primitives, In contrast, complex organisms refer to those organisms that have higher and complex level of structural and functional organisation. These are more advanced and said to have arisen from simple organisms.

Some members of a population have traits (genes) which enable them to grow up and reproduce at a higher rate and leave more surviving offspring in the next generation than others.

Maintenance of constant internal conditions by organisms for survival. This is achieved by regulating metabolic processes.

Term used by Carl Woese for the first cells which presumably gave rise to three equally ancient cell lines : archaebacteria, eubacteria and eukaryotes.

Evolutionary features of mammals:
(i) Mammals become viviparous and protected their unborn young ones inside the mothers body.
(ii) They are more intelligent (with increased brain size) in sensing and avoiding danger.

Genetic variation is essential for a species to survive in a changing environment.
The environment keeps on changing as geological, meteorological and biological processes continuously modify it.
The presence of variation ensures that at least a few individuals in a population will be suitably adapted to new environment and evolve.

1. Ernst Haeckel proposed embryological support for organic evolution.
2. It was disapproved by Ernst Von Baer.
3. He noted that embryos never pass through the adult stage of other animals.

Industrial melanism is an example of Darwin's theory of natural selection. Before industrial revolution in England the environment was unpolluted. The lichens on the barks of trees were pale. The white-winged moths could easily camouflage, while the dark winged were spotted out by the birds for food. Hence, they could not survive. After industrial revolution the lichens became dark disappeared (due to pollution and soot deposit). This favoured the dark-winged moths while the white-winged were picked by birds. The population of the former which was naturally selected increased This shows that in a mixed population those which can adapt in abetter way with the changing environment survive and increase in population, Thus industrial melanism in this way supports Darwin's theory of natural selection.

The process of evolution of different species from one species in a given geographical area starting from a point and radiating or spreading to other geographical areas or now habitats is called adaptive radiation. This is called as divergent evolution as this involves the formation of different functional forms of basically similar structures, e.g. Darwin's finches and Australian marsupials. However when more than adaptive radiation appeared to have taken place in different habitats of an isolated geograpical area, the adaptive radiation can be referred to as convergent evolution. This involves the development of similar adaptive functional structures in unrelated groups of organisms e.g. Australian marrupials and placental mammals-Placental wolf-Placental wolf and Tasmanian wolf.

Difference between divergent and convergent evolution:

Palaeontology is the study of past life based on the fossil record.

Darwin explained it as the process of evolution of different species in  given geographical area starting from a point and literally radiating to other areas of geography called adaptive radiation.
By the process of evolution many other forms with altered beaks arose from the original seed-eating features, enabling them to become insectivorous and vegetatian finches.

Role of genetic variations in evolution:
1. Genetic variability is necessary for evolution. They are the raw materials of evolution.
2. Genetic variations in a population arise due to two different mechanisms. They are gene migration and genetic drift.

De Vries Mutation theory:
Hugo de Vries (1848-1935) was a Dutch Botanist. He performed experiments on the Evening Primrose.
According to this theory, new species arise suddenly showing abrupt deviations in characters from the normal forms. Thus evolution in not a slow and gradual process but a sudden discontinuous and jerky process.

Kinds of selections:
1. Stabilising selection
2. Directional selection
3. Disruptive selection.

Biogeography means the study of geographical distribution of species. Darwin joined as an unpaid naturalist on a five-year navigational mapping of British Admiralty abrod the ship H.M.S. Beagle.

During his voyage Darwin observed and studied a wide variety of plants and animals on continents and in distant seas. Darwin studied on different continents different species. He found different species. He found different species in mainland and islands and showed evolutionary relation of species with biogeography.
Darwin studied birds called 'finches' which resemble with original birds of main land from Galapago islands separated. He also noticed giant tortoise, metre long marine and land iguanas, many unusual, plants, insects, sea shell. All these varieties of organisms influenced Darwin to think about evolutionary changes.