● During his journey `color{Brown}"Darwin"` went to `color{Violet}"Galapagos Islands"`.

● There he observed an `color{Violet}"amazing diversity"` of creatures.

● Of particular interest, `color{Violet}"small black birds"` later called `color{Violet}"Darwin’s Finches"` amazed him.

● He realised that there were `color{Violet}"many varieties"` of finches in the same island.

● All the varieties, he conjectured, `color{Violet}"evolved on the island"` itself.

● From the original `color{Violet}"seed-eating features"`, many other forms with `color{Violet}"altered beaks arose"`, enabling them to become `color{Violet}"insectivorous and vegetarian"` finches.

● This process of evolution of `color{Violet}"different species"` in a given geographical area `color{Violet}"starting from a point"` and literally `color{Violet}"radiating to other areas"` of geography (habitats) is called `color{Brown}"adaptive radiation"`.

● `color{Violet}"Darwin’s finches"` represent one of the best examples of this phenomenon.

● Another example is `color{Brown}"Australian marsupials"`.

● A number of `color{Violet}"marsupials"`, each different from the other evolved from an `color{Violet}"ancestral stock"`, but all within the `color{Violet}"Australian island"` continent.

● When more than `color{Violet}"one adaptive radiation"` appeared to have occurred in an `color{Violet}"isolated geographical area"` (representing different habitats), one can call this `color{Brown}"convergent evolution"`.

● `color{Violet}"Placental mammals in Australia"` also exhibit adaptive radiation in evolving into varieties of such `color{Violet}"placental mammals"` each of which appears to be ‘similar’ to a `color{Violet}"corresponding marsupial"` (e.g., Placental wolf and Tasmanian wolf marsupial).

● Evolution by `color{Brown}"natural selection"`, in a true sense would have started when `color{Violet}"cellular forms of life"` with differences in metabolic capability originated on earth.

● The essence of `color{Brown}"Darwinian theory"` about evolution is `color{Violet}"natural selection"`.

● The `color{Violet}"rate of appearance"` of new forms is linked to the `color{Violet}"life cycle"` or the `color{Violet}"life span"`.

● Microbes that `color{Violet}"divide fast"` have the ability to multiply and become `color{Violet}"millions of individuals"` within hours.

● A colony of `color{Violet}"bacteria (say A)"` growing on a given medium has `color{Violet}"built in variation"` in terms of ability to `color{Violet}"utilise a feed"` component.

● A change in the `color{Violet}"medium composition"` would bring out only that part of the `color{Violet}"population (say B)"` that can survive under the new conditions.

● In due course of time this `color{Violet}"variant population outgrows"` the others and appears as new species.

● This would `color{Violet}"happen within days"`.

● For the same thing to happen in a `color{Violet}"fish or fowl"` would take `color{Violet}"million of years"` as life spans of these animals are in years.

● Here we say that `color{Violet}"fitness of B"` is `color{Violet}"better"` than `color{Violet}"that of A"` under the new conditions.

● `color{Violet}"Nature"` selects for `color{Violet}"fitness"`.

● One must remember that the `color{Violet}"so-called fitness"` is based on characteristics which are `color{Violet}"inherited"`.

● Hence, there must be a `color{Violet}"genetic basis"` for getting selected and to evolve.

● Another way of saying the same thing is that some organisms are `color{Violet}"better adapted"` to survive in an `color{Violet}"otherwise hostile environment"`.

● `color{Violet}"Adaptive ability"` is inherited. It has a `color{Violet}"genetic basis"`.

● `color{Violet}"Fitness"` is the end result of the `color{Violet}"ability to adapt"` and get `color{Violet}"selected by nature"`.

● `color{Violet}"Branching descent"` and `color{Violet}"natural selection"` are the two key concepts of `color{Brown}"Darwinian Theory"` `color{Brown}"of Evolution"`.

● Even before Darwin, a `color{Brown}"French naturalist Lamarck"` had said that evolution of life forms had occurred but `color{Violet}"driven by use"` `color{Violet}"and disuse of organs"`.

● He gave the examples of `color{Violet}"Giraffes"` who in an attempt to `color{Violet}"forage leaves on tall trees"` had to adapt by elongation of their necks.

● As they passed on this acquired `color{Violet}"character of elongated neck"` to succeeding generations, Giraffes, slowly, over the years, came to `color{Violet}"acquire long necks"`.

● `color{Violet}"Nobody believes"` this conjecture any more.

● `color{Brown}"Is evolution a process"` `color{Brown}"or the result of a process"`?

● The world we see, `color{Violet}"inanimate and animate"`, is only the success `color{Violet}"stories of evolution"`.

● When we describe the story of this world we describe `color{Violet}"evolution as a process"`.

● On the other hand when we describe the `color{Violet}"story of life on earth"`, we treat evolution as a `color{Violet}"consequence"` of a process called `color{Violet}"natural selection"`.

● We are still not very clear whether to regard `color{Violet}"evolution and natural selection"` as processes or end result of unknown processes.

● It is possible that the work of `color{brown}"Thomas Malthus1"` on populations influenced `color{brown}"Darwin"`.

● `color{brown}"Natural selection"` is based on certain `color{Violet}"observations"` which are `color{Violet}"factual"`.

● For example, `color{Violet}"natural resources"` are limited, `color{Violet}"populations"` are stable in size except for `color{Violet}"seasonal fluctuation"`, members of a population `color{Violet}"vary in characteristics"` (in fact no two individuals are alike) even though they look `color{Violet}"superficially similar"`, most of variations are inherited etc.

● The fact that theoretically `color{Violet}"population size"` will `color{Violet}"grow exponentially"` if everybody reproduced maximally (this fact can be seen in a `color{Violet}"growing bacterial population"` and the fact that population sizes in `color{Violet}"reality are limited"`, means that there had been `color{Violet}"competition for resources"`.

● Only `color{Violet}"some survived"` and grew at the `color{Violet}"cost of others"` that could not flourish.

● The `color{Violet}"novelty and brilliant insight"` of Darwin was this: he asserted that `color{Violet}"variations"`, which are heritable and which make `color{Violet}"resource utilisation better"` for few (adapted to habitat better) will enable only those to reproduce and leave more progeny.

● Hence for a period of time, `color{Violet}"over many generations"`, survivors will leave `color{Violet}"more progeny"` and there would be a change in `color{Violet}"population characteristic"` and hence `color{Violet}"new forms"` appear to arise.