Causes of Variation

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Variation is central to life itself. Variation is what makes every single individual... an individual. Without variation, the evolution of different species would not be possible. What is the cause of variation?


Genes

Genes dictate what proteins our body makes, when, where and how, and are ultimately responsible for the way we look and function. It's not just what genes we have though, it's also about whether they are switched on or off, when they are switched on or off, and in which particular cells they are switched on or off. Us and chimps share a great deal of our genotype (genetic makeup), more than 98%, yet we can agree that there are significant differences between us that make us distinct species.

Features such as height, predisposition to illness, height and weight, or even behaviours such as risk-taking have been linked exclusively or partly to certain genes.


Environment

The environment is not just what most people associate with the word. It's not just the temperature of the room you live in - it's everything outside our bodies which exert their influence on it. Which is pretty much everything from family to friends, to the internet and to diet, exercise, culture and beyond. The environment in the womb where we grew had an impact on our bodies. Even the environment of genes themselves has an impact on their activity.

Genes won't result in the variation seen in a professional body building contest. Those physiques were achieved by the manipulation of one's environment by doing certain activities.


A complex interplay between both

Genetic and environmental factors combined often account for a lot of variation. Twin studies are a popular method of isolating genetic factors from environmental factors and vice versa. Monozygotic twins share the same genes, while dizygotic twins do not. When an incidence of a certain condition, e.g. schizophrenia, is higher between monozygotic twins compared to the general population, it can be deduced that a genetic component is accountable for the condition.

Genes may be responsible for one's weight, yet environmental factors like lifestyle, diet, exercise or surgery can change someone's weight and either bring it closer to the mean, or further away towards the extremes.
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