Evolution, technically speaking is nothing more than(Delta G / Delta T). In other words, it is basically nothing but a change in the genes (a population's "gene pool") over a certain time period. Technically, this is all evolution is! It must also be known that there are several modes and types of evolution. Evolution is not only one species giving rise to another (macro or mega evolution), but because evolution simply refers to a change in the genes, it is basically the study of diversity! Evolution is heavily dependant on the mode of reproduction (sexual or asexual) a particular species has. The mode of reproduction is most important due to:

Asexual Reproduction = a simple form of reproduction where reproduction takes place without "sex" or the union between sperm and egg. Asexual reproduction is a simple process where the young are the result of detached portions of the single parent, without intervention from the opposite sex. For example, there exists a certain species of frog that can have young without ever mating with the opposite sex. This is asexual reproduction. Asexual reproduction is relevant to evolution simply because it must be known and understood that all young born by asexual means are genetically identical to their "parent".

Sexual Reproduction = is a more "complex" form of reproduction where as it involves the "union or fusion" of a "male" and "female" gamete or sex cell (ie sperm or egg). Sexual reproduction is relevant to evolution because it creates genetic variability and genetic diversity within the offspring (this occurs because the offspring get a random assortment of "mom and dad's" chromosomes). Sexual reproduction in most environments is an extremely valuable attribute to possess.

The following is an example of a situation showing how evolution occurrs and the value of the mode of reproduction.

Suppose there are two lakes. One lake contains a species of guppy that reproduces asexually (all young are thus gentically identical to eachother and their parent). The other lake contains a species of guppy that reproduces sexually (the genetic codes of the young are not identical to eachother or their parent, they are gentically diverse). Now suppose a fungus gets introduced into the lake containing the guppies that reproduce asexually.

What now happens is that every single guppy will become infected. Next, the fungus gets introduced into the lake containing the guppies that reproduce sexually. The result in this lake is that only 50% of the guppies get infected.

This is a real life example of the value of your mode of reproduction and how it relates to evolution. The asexual guppies are "genetic clones" of eachother and thus "bet all their money on one lottery ticket" (so to speak) Sadly, that "lottery ticket" was not a winner and got infected. They were an easy target for extinction. However the "sexual guppies" had genetic diversity (multiple lottery tickets!), so the fungus could not easily adapt to them! The genetic variability/diversity the sexual guppies possess allowed them to live on and create future populations. Thus the sexual guppies were better adapted ( ie more "fit") to resisting fungal infection than the asexual guppies. This is all relevant because what we have here is a concrete case illustrating the process known as "natural selection"

Natural selection is the primary mode by which evolution works on populations.

**Note**

Genetic variability and diversity are not only obtained through sexual reproduction. (If that was the case, asexual species would never "evolve"). Variability can also be obtained through what is known as a genetic mutation. Genetic mutations can occur in both sexual and asexual creatures.