Speciation is the evolutionary process by which new biological species arise. A new species will be a group of individuals distinguished from the original one because by nature only interbreeding takes place amongst their own species. The original group will not or cannot reproduce with the new species. When this happens, they can be called two independent species. In this sense, each species is the biggest gene pool possible under natural conditions.

While talking about new species there are a few things to remember. A new biological species is defined on the basis of members actually or potentially interbreeding in nature, and not according to similarity of appearance. Although appearance is helpful in identifying species, it does not define species. Many characteristics can vary within a single species. For example, these happy face spiders look different, but since they can interbreed, they are considered the same species: Theridion grallator

The plant hydrangea can have pink "flowers" or blue "flowers" (they're actually modified leaves). But we do not classify the two forms as different species. In fact, one could allow a blue-"flowered" plant to become a pink-"flowered" plant just by changing the pH of the soil and the amount of aluminum taken up by the plant!

Further, in nature, there are quite a few places where the biological definition of a species can run into some difficulty. In the case of organisms that reproduce mainly asexually, like the bacteria, the definition of a species as a group of interbreeding individuals cannot be easily applied. The bacterium shown here is reproducing asexually, by binary fission. Since the new bacterium divide themselves we cannot strictly apply the definition.

Then again, there are many instances of plants and some animal species, for example two lineages of oak look quite different, but occasionally form hybrids with each other; hooded crows and carrion crows, which largely mate within their own groups and look different but in some areas they hybridize. Should they be considered the same species or separate species?

Therefore, speciation is a lineage-splitting event that produces two or more separate species. What are the main ways for it to occur? There are four modes of natural speciation, based on the extent to which speciating populations are geographically isolated from one another: allopatric, peripatric, parapatric, and sympatric. Speciation may also be induced artificially, through animal husbandry or laboratory experiments.

Allopatric Speciation(geographic isolation)

During allopatric speciation, a population splits into two geographically isolated allopatric populations. New speciation starts because populations are prevented from interbreeding. Scientists think that geographic isolation is a common way for the process of speciation to begin: rivers change course, mountains rise, continents drift, islands break away from the main lands, habitats fragment and become unfavourable, organisms migrate, and what was once a continuous population is divided into two or more smaller populations.

Peripatric Speciation (Mostly Geographic)In peripatric speciation, new species are formed in isolated, small peripheral populations which are prevented from exchanging genes with the main population. For instance if a few members of a species, like fruit flies larvae in a bunch of rotting banana, get washed ashore to an island from the mainland after a storm, they will inbreed amongst themselves as they grow up and form an isolated population. If by chance

they carry some genes that are rare in the mainland population these small differences, which are rare on the mainland, drift to fixation in the small population on the island over the course of a few generations (i.e., the entire island population ends up having these genes). It may be that one of these rare genes happens to cause a slight variation in the mating dance. Another gene causes a slight difference in the shape of male genitalia. The essential characteristic of this mode is that genetic drift plays a role in speciation.

In peripatric speciation, small population size would make full-blown speciation a more likely result of the geographic isolation because genetic drift acts more quickly in small populations. Genetic drift, and perhaps strong selective pressures, would cause rapid genetic change in the small population. This genetic change could lead to speciation.

Parapatric Speciation (somewhat geographic)In parapatric speciation, the zones of two diverging populations are separate but do overlap. There is only partial separation afforded by geography, so individuals of each species may come in contact or cross the barrier from time to time, but reduced fitness of the heterozygote leads to selection for behaviours or mechanisms which prevent breeding between the two species.Ecologists refer to parapatric and peripatric speciation in terms of ecological niches. A niche must be available in order for a new species to be successful.

Sympatric Speciation (non-geographic)In sympatric speciation, species diverge while inhabiting the same place. The population is continuous, but nonetheless, the population does not mate randomly. Individuals are more likely to mate with their geographic neighbors than with individuals in a different part of the population's range. Examples of sympatric speciation are found in insects which become dependent on different host plants in the same area. There is no specific extrinsic barrier to gene flow but they breed within their host plants.

For example, 200 years ago, the ancestors of apple maggot flies laid their eggs only on hawthorns, which are native to America. But today, these flies lay eggs on hawthorns and domestic apples that were introduced by immigrants and bred there. Females generally choose to lay their eggs on the type of fruit they grew up in, and males tend to look for mates on the type of fruit they grew up in. So hawthorn flies generally end up mating with other hawthorn flies and apple flies generally end up mating with other apple flies. This means that gene flow between parts of the population that mate on different types of fruit is reduced. This host shift from hawthorns to apples may be the first step toward sympatric speciation-in fewer than 200 years, some genetic differences between these two groups of flies have evolved.

Artificial SpeciationNew species can be created by domesticated animal husbandry for better and yield. For example, a new species of domestic sheep were created by hybridisation that no longer produced viable offspring with the parent species. Domestic cattle on the other hand, with several varieties such as jersey, holstien, and Indian varieties like the kherigarh etc., could not be speciated as they willingly and readily reproduce, with several related "other" species producing fertile offspring.

The best documented creations of new species in the laboratory were performed in 1989 by the scientist Diane Dodd. Rice and salt bred fruit flies, 'Drosophila melanogaster' were bred using a maze with three different choices such as light/dark and wet/dry. Each generation was placed into the maze and the groups of flies which came out of two of the eight exits were set apart to breed with each other in their respective groups. After thirty-five generations, the two groups and their offspring would not breed with each other even when doing so was their only opportunity to reproduce.Diane Dodd was also able to show allopatric speciation by reproductive isolation in Drosophila pseudoobscura fruit flies after only eight generations using different food types, starch and maltose. Dodd's experiment has been easy for many others to replicate, including other kinds of fruit flies and foods.