Variations in human and causes of variation:

The different in characters such as height, color , etc among individuals of the same species are called variation.  It plays very important role in evolution. Variation may be caused either by the effect of environment or by the changes in the genetics material. Environmental variation are caused by effect of the environment and they can not be inherited to the offspring. For example: development of muscles in athlete, the boring of pinna or nose for putting on jewelry, loss of some body parts due to  accident or disease are some of the environmental variations. Such variations have no significance in the process of evolution. In contrast to the environmental variation, the changes in genetics material produce genetics or habitable variation. They are considered as raw material evolution. Depending upon the effect they produce

                                             example of variation in humans: 

 variation can be divided into two groups .

1. Continues variation:

                                  Refers to small differences in characters of the member of species. Height, skin, color, skin, intelligence, eye color, etc are some of the examples of continues  variations. Such variations are neither purely genetically nor purely environmental. They appear to be the combination of both environmental and genetics Factors.

2. Discontinuous variation:

                                    Sudden and Sharp differences among the member of same species. They are heritable as they are purely caused by the genetic materials. Blood groups, six fingers, in hand or foot, tongue rolling etc are some of the common examples in man. 

CAUSES OF VARIATION

Following some causes of importance in variation

i) Independent assortment of chromosomes:

               During metaphase of first meiotic division homologous chromosomes come together in the pairs and subsequently Segregate into the daughter cells independence of each other. produce more varieties of gametes.

ii) Crossing over:

           It is the process of mutual exchange of equal of chromatics of non-sister chromatics  of a pair of homologous chromosomes during  prophase-I  of  first meiotic division. Through crossing over, indefinite combinations of alleles (genes controlling common characters) are made possible.

iii) Fertilization: 

                   The set of alleles carried by chromosomes of each gamete is and always differs to a more  or less extent than the others. Since a number of male gametes are available to fertilize female gamete. Thus different combination of characters in individual are possible as a result of fertilization of egg with either of male gamete.

iv) Mutation: 

          It has a common observed that some individuals of a population of an organism show strikingly different characters than the others. For example: some persons around you might have six fingers in hands or feet. The phenomenon of producing such changes is called mutation. It can be defined as a sudden change in the genetic material. It is the most important source of heritable variation among the organisms which is considered as the starting point of new species. 

v) Environment: 

               A number of body cells affected by the environment. For instance, change in pigmentation of skin upon the extent of exposure to sun-light or the development of muscles  due to exercise etc. whenever such variations are non-heritable.