In the past, those of our ancestors who were best adapted to the environment passed on their genes to their offspring. Today, medical advances have allowed those that would not previously have survived to reproduce and contribute to the human gene pool. The benefits to the individual person are obvious. However, due to the size of our population, this has little effect on the overall genetic make-up of our species. The major consequence of medicine has been the increase of genes that have little or no resistance to disease. In the future, there will be a greater reliance on medicine for survival rather than genetic adaptations.
Infectious diseases are one of the major causes of human mortality and were responsible for over 25 per cent of all deaths in developed nations prior to the introduction of antibiotics in the 1940s. The application of vaccinations and antibiotics has reduced this figure to about 1 per cent. Unfortunately, not all humans share such access to modern medicine and preventable infectious disease remains the largest killer of people in developing nations, accounting for over 40 per cent of all deaths. In the developed world, over-use of antibiotics has led to most of the harmful bacteria becoming immune, so that many infectious diseases are once again becoming significant killers.
The last century has seen a tripling of newborn life expectancy in developed nations. This means that nearly all children in those countries will survive childhood and live to the age that they can reproduce. This, rather than increased adult survival, is one of the major causes behind the increase in average life expectancy, and is linked to improvements in medicine and hygiene.
An interesting consequence of improved medical technology is that humans can now reproduce, or prefer to reproduce, at a later age. This increases the chance of a mutation occurring in the sex cells and being passed on to offspring. The long-term effect is that more genetic mutations, and hence variation, will be introduced into the human gene pool.
Fixing our genes: the human genome project
This research project, overseen by the Human Genome Organisation, is locating and mapping every gene contained in human DNA. By knowing the position of each gene, it is possible to understand what they do and how genetic diseases arise. The impact of this will be felt in every area of biology and medicine throughout the next century, with huge implications for the prevention and diagnosis of disease. Scientists predict that some potential diseases will be cured at the molecular level before they arise in an individual.
Technology has helped us to become the first species capable of adapting the environment, to a certain degree, to suit ourselves. This has reduced the need to rely on genetic adaptations like our ancestors did in the past. We now have the ability to live in any climate and, assisted by transportation, have become a global species.
Technology has also had a negative impact on our species. It has been responsible for the deaths of millions- through war, environmental pollution and degradation and the introduction and spread of disease.
Technology and the end of isolation
In the past, our ancestors lived in small, isolated populations, where inbreeding was common and genetic mutations could spread easily. Over time this could lead to the evolution of a new species. We now live in a highly populated world where we have the ability to travel anywhere and potentially share our genes with anyone. The end of isolation has significantly reduced the chance of evolutionary change.
The impact of agriculture on human evolution
The role of agriculture was important in the development of civilisation and the ability to sustain large populations of people. It has also been responsible for the introduction of diseases, such as smallpox and measles, which developed from diseases plaguing domestic animals about 10,000 years ago. Although farmers eventually evolved genes resistant to these diseases, hunter-gatherers died in droves when they were first affected.
Genetic adaptations evolving from agricultural lifestyles
Many groups have developed specialised eating habits due to their lifestyle. One such habit that has been identified as a genetic trait is the ability to digest milk as an adult. All infant mammals rely on milk for sustenance but, as they grow older, the enzyme that digests lactose (a sugar found in milk) disappears. This means adult mammals cannot normally tolerate milk. However, as a result of an agricultural ancestry, some adults, like the Masai of Kenya, the Beduoin and most Europeans, are still able to digest milk. Others, such as Australian Aborigines and west and central Africans, find milk indigestible. This adaptation probably only evolved in the last 10,000 years as agriculture developed and animal milk was collected and consumed.
Will we become extinct?
The fossil record demonstrates that all organisms exist for a limited time span and then become extinct. This suggests that extinction would also be the expected outcome for our own species. Some of the extinction events in the past, such as meteorite or comet impacts, are beyond our control. Most other causes of extinction, including major climate change, can now be overcome by technology, if we are willing to act. Although technology may allow us to avoid the fates of all other species, if we are not careful how we use it, technology could also lead to the destruction of our planet.
Meteorite or comet impact
Major collisions like this are a statistical certainty in the Earth's future, and would be catastrophic for most species. The ‘nuclear winter’ that could follow the impact would profoundly disturb global ecology, leading to mass extinction. Around 500 meteorites hit the Earth each year, with most landing in the oceans.
Spread of plagues and viruses
In the age of travel it is easy for disease to become pandemic (widespread) overnight. Crowded cities and poor hygiene are breeding grounds for many of these organisms. New strains of virus and bacteria can develop rapidly, with new types emerging that we are not aware of and that we may not be able to fight effectively.
The worst pandemic in modern times was the bubonic plague or Black Death (caused by the bacteria Yersinia pestis) which occurred in Europe between 1346 and 1353. Over one third of the population died from this disease. Other outbreaks occurred over the centuries but the plague is now eradicated from Europe, although it still exists in other regions of the world.
Destruction of the biosphere
We are the only species capable of destroying the biosphere. Many ecosystems have now been lost through pollution, land clearance,climate change and overpopulation. We cannot have such an affect on our planet without feeling the impact of our actions in the future.