Consider various human characteristics, such as height, weight, skin color, head

Question

Consider various human characteristics, such as height, weight, skin color, head form, and eye shape. Are the phenotypic expressions of these characteristics discontinuous (able to be assigned to discrete categories) or continuous ( on continuum rather than separable into discrete categories)? What might they tell us about the mechanism behind human variation? Consider various human characteristics, such as height, weight, skin color, head form, and eye shape. Are the phenotypic expressions of these characteristics discontinuous (able to be assigned to discrete categories) or continuous ( on continuum rather than separable into discrete categories)? What might they tell us about the mechanism behind human variation?

Explanation / Answer

Ans: Variation is one of the most critical aspects of species survival. Inherited (heritable) characteristics are those traits which are passed on to offspring directly from their parents. These traits are passed on by way of the genetic material that is combined from the parents during the process of sexual reproduction. There are two kinds of inherited variation i.e., continuous variations and discrete variations.

Continuous variations are the differences in characteristics that have a range of possible variations such as height, shoe size, hand span, skin color, hair color etc. While discrete variations are the differences in characteristics that have a definite form, with a limited number of possibilities. This includes those individuals within a species that have either one characteristic or the single other variation of the characteristic and their examples include tongue rolling ability, blood groups, earlobe attachment, hairline etc

Non-inherited characteristics are acquired and are not necessarily passed on from generation to generation. Athleticism, artistic ability, leadership qualities are all learned during the early years of life. Some variations may be influenced by interactions with the environment.

Phenotype is the way the trait actually appears, functions, or behaves and examples includes tall, short and eye color etc. While genotype is the gene combination found in the organism chromosomes examples includes TT, Tt, tt.

Dominant genes is a gene that will always appear even if it is paired with a gene for the opposite trait. T is dominant for tall and t is for short, Tt = tall. While recessive genes are the genes that does not appear if paired with a gene for the opposite trait and it will appear if it is paired with another gene like itself T is dominant and t is recessive, Tt is for tall and tt is for short. The variation in weight in human populations is an example of discrete or continuous variation. There is a wide range of weights an individual can be. Both genetic and environment influence this trait.

Causes of Human variation includes genetic variation which is the differences between individuals that are caused by genes inherited from their parents. While environmental Variation is the differences between individuals caused by environmental factors (climate or habitat) on an organism phenotype. Cultural variation for humans, culture is an important source of environmental variation.

For natural selection to work three preconditions must be fulfilled, the trait in question must be inherited: specific trait must be genetic or inherited from the parents the trait in question must show variation between individuals higher animals are genetically unique so their traits can be selected or not selected. The filter between the organism and its genetic make up is the environment which must exert some pressure in order for natural selection to act

For polymorphisms adaptivity some are certainly adaptive i.e., body size, skin colour while some are neutral i.e., ABO system. Some may be linked to disease resistance i.e., type A fights off smallpox and typhoid, bronchial phenomena while type B fights off the bubonic plague.

Mechanism for evolutionary change which results from a nonrandom change in the genetic code. Mutations are the source of all genetic variation as they introduce new alleles into a population and thus change the frequency of different alleles over time. Mutations can have different effects depending on the specific type of mutation and the environment. Mutations can also be benificial and lead to changes which improve the survival and reproduction of organisms. Mutations are vital to evolution because they provide new variations. Mutation are rather random and we can not predicting when they will take place. They can be caused by a number of environmental factors including background radiation, heat and ingested substances such as caffeine. Mutations can take a place in any cell of the body. To have evolutionary importance, mutation must occur in a somatic cell.

Adaptive radiation is the formation of many new species following the availability of new environments or the development of a new adaption event in which lineage rapidly diversifies with the newly formed lineages evolving different adaptations. Rapid diversification of mammals may constitute an adaptive radiation.

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