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.

Coacervates lacked complex molecular organization, enzymes, electron transport chain, and precise control of nucleic acids.

1. The biodiversity we see today is the story of evolution, i.e. evolution is considered as a process, that has resulted in various life forms.
2. If we talk about the life on earth, evolution is considered as a consequence of the process, called natural selection.
3. It is difficult to decide, whether evolution and natural selection are processes or results of some unknown processes.

Origin of Universe:
The universe is about 20 billion years.
The Big Bang theory explains that the universe arose from a huge explosion (unimaginable in physical terms), of a very large entity.
As the universe expanded, the temperature decreased; hydrogen and helium were formed sometime later.
The gases condensed under gravitation and formed the galaxies of the present day universe.
Earth was supposed to have been formed about 4.5 billion years back.

Paleontology is the study of fossils. It indicates
(i) The geological time period in which the organisms existed.
(ii) that life forms varied over time and certain life forms are restricted to certain geological time spans.
(iii) that new forms of life have appeared at different times in the history of earth.

Factors affecting allele frequency in populations are described below:
(i) Mutations: These are sudden heritable changes which are supposed to be the primary source of genetic variation. They are of following two types.
(a) Chromosomal Mutations: They arise due to changes in chromosome number and changes in structure.
(b) Gene Mutations: These are changes in gene structure and expression due to addition, deletion, substitution or inversion of nucleotides.
(ii) Non-random Mating: Repeated mating between individuals of certain selected traits changes the gene frequency, e.g., selection of more brightly coloured male bird by a female bird may increase the gene frequency of bright colour in the next generation.
(iii) Gene Flow (Gene Migration): It is the movement of alleles into and out of a gene pool. Breeding of immigrants with the host population adds new alleles to the gene pool of the host population.

(a) The variations in the beaks are adaptations to their food habit fresh- eating, insectivorous or seed/ fruit-eating.
(b) Darwin conjectured that all the varieties must have evolved on the same island itself.
From the original seed-eating features, other forms with altered beaks arose, enabling them to become insectivorous and vegetarian finches.
This process of evolution of different species in a given geographical area, starting from a point and literally radiating to other geographical areas, is called adaptive radiation.

(i)  Neanderthal man lived in near east and Central Asia, between 1,00,000-40,000 years before.
(ii) His brain capacity was 1400 cc.
(iii) He used hides to protect the body.
 He buried the dead. His brain size was more (1400 cc) than that of Homo erectus which was 900 cc.

Adaptive radiation is the evolutionary process in which a common ancestor evolves into a number of species, in a given geographical area, starting from a point and literally radiating to other areas of geography.
A number of Australian marsupials, each different from the other, evolved from an ancestral stock, all within the Australian island continent.
When more than one adaptive radiation appeared to have occurred in an isolated geographical area, representing different habitats, it can be called convergent evolution.
Placental mammals of Australia also exhibit adaptive radiation in evolving into varieties of such placental mammals, each of which appears to be 'similar' to a corresponding marsupial, e.g. Bob cat resembles Tasmanian tiger cat.
Lemur - Spotted cuscus.
 Anteater - Numbat.

Theory of chemical evolution or abiogenesis was proposed by Oparin and Haldane.
It states that the first form of life could have come from pre-existing non-living organic molecules (like RNA, proteins, etc.) and that formation of life was preceded by chemical evolution, i.e. formation of diverse organic molecules from inorganic constituents.
Miller's experiment:
He created conditions similar to the primitive earth in the laboratory.
Electric discharge was produced (by using electrons) in a closed flask, containing methane, hydrogen, ammonia and water vapour.
The temperature was kept at \(800\)\(^{ \circ }{ C }\). 
 After a week, he observed formation of amino acids.
Such molecules must have reacted among themselves to form giant, self-replicating molecules, the first form of life.

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.