Can we predict the future?
Many of the predictions for the future appearance of humans are based on past trends or on the fanciful idea that body parts used more frequently will get larger, or those that are used less will shrink. Will technology replace our need for strong limbs? Will too much television cause humans to evolve square eyes? Will we have the abnormally large brains commonly seen in science fiction movies?
Most of these predictions are not based on the principles of biology and evolution. While we do not know what events will happen in the future that may affect the way we evolve, it is possible to set some constraints on what could happen. Some of the suggested changes are highlighted below.
Although we have smaller jaws than in the past, and less room for all 32 adult teeth, it is probable that no significant change will occur in the number of teeth. However, if we change the way we eat (perhaps food in the future will be softer and require less chewing) then we may see some reduction in our jaws and more crowded teeth.
Our brains are unlikely to get proportionally larger as any significant change in size would affect the ability for a baby’s head to pass through the pelvis during birth. The pelvis is a compromise between an upright posture, bipedalism and the size of the birth canal. Changing this would alter a woman’s ability to walk efficiently.
Although the past trend within our species has generally been toward smaller brains, this was probably due to a decrease in body size. We may not use all of our brain today, but for a smaller brain to become common in our species there would have to be an advantage in such a characteristic. There is a direct relationship between our brain size and body size and this relationship is unlikely to change.
The trend over the last 300 years has been toward larger bodies, but this cannot continue indefinitely. Size cannot increase beyond a certain limit as the mechanical demands on the tissues of very large bodies are different to bodies of medium sizes. By significantly changing the size of the body, there would need to be a change in the shape of the body.
Recent reports show that there's a whole generation of teenagers with overdeveloped thumbs due to playing too many video games. Muscles are able to adapt through excessive physical use, but this is not genetic. An individual may develop such a characteristic but will not pass this on to any offspring.
A grand averaging?
Many geneticists claim that something new is happening in human evolution - something along the lines of a 'grand averaging' of our species. Basically, we are becoming more alike.
Human evolution relies on the differences in our genes and in our ability to pass on these genetic differences (ie our breeding capabilities). Over time, the population should change as these differences become more apparent. If the genetic changes are great enough, a new species will arise. However, the three components required for evolution to occur - variation, natural selection and geographic isolation - have more or less disappeared from the equation.
Humans can be considered a single genetic 'continent' - meaning that the world's population is mixing and is no longer just breeding within cultural or ethnic groups. It is suggested that, given enough time, the human race will start to look more and more alike, becoming the 'average' of all the current different physical appearances.