Sunday, April 24, 2011

Human evolution is still occurring

        Evolution, what is it really? For simplicity reasons, its change through time; short or long time periods. Evolution has shaped and still is; the diversity in our world. Your evolution from your ancestors diverged from similar primates. Hominoid evolution has dated back to over 6million years ago. Yes, fossils are a key importance in the discovery of our evolution, but there are other forms of discovery and interpretation in which play a contributing part. Recent research indicates that humans today are in fact evolving more rapidly and the rate of change has sped. Two factors for this is the population growth, which inevitably increases the gene pool in which mutations take place. The environment differs from place to place and these changes could cater for the mutations to take effect.

        Skin colour variation is a key factor in our evolution; it is the obvious variation as to why humans differ from each other. This has not been the case for very long; in fact, skin colour only began to change when migration out of Africa and loss of body hair became a factor. In regions of high ultraviolet (UV) radiation from the sun, such as Africa, where the earliest members of our lineage (2 million years ago) lived, they would have had body hair to protect their fairly light skin beneath from the sun (such as apes). As evolution progressed the body hair was slowly eliminated to cater for the hot conditions, as a result of this the melanin (our skin pigment; natural sun-screen) evolved dark skin, through natural selection to prevent sun damages, injury or cancers, by protecting the skin and sweat glands. Therefore, darkly pigmented skin evolved, protecting destruction of nutrients like folate in our bodies from UV radiation. 

        You may ask, well then, ‘‘Why the need for white skin?’’. Well easy, in regions of low UV radiation from the sun the skin needs light skin in order to absorb sunlight, which sunlight stimulates the synthesis of vitamin D in our bodies, preventing diseases. When did this environmental change occur? When our human ancestors migrated out of Africa (in the last million years), the range of skin colouration was a result of the widespread colonization of our world. The selective processes take place in order to protect us from the sun and to provide as with sufficient amounts of vitamin D synthesis. Recent genetic studies indicate that skin colour could rapidly change over as few as 100 generations, or about 2,500 years, with the influence of the environment. You may be thinking then, ‘why is there mixed, black and white people in most regions in the world?’ This is merely because we have the ability to move around the world quickly (airplanes, boats and other). Among humans, race has no taxonomic (technique of classification) significance, as all people belong to the same hominid subspecies, Homo sapiens sapiens.


  Homo sapiens sapiens


        Lactose intolerance for cow’s milk is described as a disease but in fact, the majority of the world’s population is affected by this. Human infants, receive nourishment from their mother’s milk (like other mammals), as they have an enzyme that allows milk sugar (lactose) to be digested, but this is generally ‘switched off’ at around four years of age, following weaning. Human beings began cultivating domestic grains and animals, sheep and then cattle which were first domesticated just over 10,000 years ago. It changed the way people lived dramatically, populations ‘boomed’ as the cultivation of most of their foods began. As a result of this, genetic changes in the enzyme allowed the digestion of milk sugar to continue through to adult-hood. Low levels of lactose deficiency are found in European populations, due to this long history of dairy farming, and highest levels in populations of Asian ancestry who were not dairy farmers. Low levels also occur in populations dependent on milk in their diet. The genetic change in lactose tolerance was prevailed throughout environments where milk is a major nutrients source and included in the diet. The lactose tolerance ‘gene’ would have been spread across the colonised world to some extent.

        Vitamin C is needed in human’s diets, it’s a nutrient found in many fresh fruits and vegetable (citrus fruits), and humans can develop a disease called scurvy without it. A frame-shift mutation in our incapability to make vitamin C has become apparent due to one of these genes being non-functional. This trait mutation is in other primates as well, and could have occurred in the ancestors of all primates (around 70-80 million years ago). This mutation maintained in the early primate ancestors as they lived in tropical regions, and ate lots of fruits, meaning the mutation was not a causable effect for them, carrying it onto all descendents. Vitamin C deficiency has only become an issue with diet changes, such as foods with high fats and lack of fresh fruit or vegetables. Our closest primates also would get ill if they didn’t maintain a strict diet of fruits and vegetables.
       So, what will humans evolve to in the future? Evolutionary predictions are speculated from what kind of environment our species may face, the climate changes could diminish the benefits of culture and medicine, creating a new era of natural selection. Relaxation in selective pressures is caused from industrialization, as diminishing energy resources become threatening, and population growth. Many would say in the future, humans will be greatly intelligent, but the larger brains and cranial of infants would need to pass through a women’s pelvis to reach the world. Greater difficulties and renewed selective pressures are most probable.

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