The strongest evolutionary pressure of all comes from infectious diseases. Millions of people die from infectious diseases each year, particularly in the poorer regions of the world. However, genes that provide an advantage against one disease may not provide an advantage when faced with another. When infectious diseases became more common in human populations, perhaps because populations grew in size and pathogens were able to spread more rapidly, people with a genetic advantage were more likely to survive and reproduce.
As a result, these genetic advantages were selected for, allowing more people to survive and fight disease. In some cases, a genetic advantage resulted from losing the full activity of a gene. A good example of this is the caspase gene.
Caspase works as a part of our immune system, responding specifically to bacterial infection. It was suggested that the caspase gene was gradually inactivated in the human population because the active gene can result in a poorer response to bacterial infection.
In a study carried out by researchers at the Wellcome Trust Sanger Institute in , it was suggested that the caspase gene was gradually inactivated in the human population because the active gene can result in a poorer response to bacterial infection. People with fully functional caspase were at a much higher risk of a fatal bacterial infection sepsis if bacteria entered the bloodstream, than people with the inactive version of the gene.
Before improved hygiene and antibiotics, survival of severe sepsis would have been a strong selective force for the inactive gene, which would have been greatly favoured.
Today, people with two copies of the inactive gene are eight times more likely to escape severe sepsis if suffering with an infectious disease and three times more likely to survive. But the study leaves us with a key question. If it is so good to have the inactive gene, why did our ancestors have an active form in the first place?
It may be because in some areas of the world having the active gene carries an equal advantage to carrying the inactive gene in other areas of the world.
What is clear however, is that all organisms are dynamic and will continue to adapt to their unique environments to continue being successful. In short, we are still evolving. It was found that women with a certain combination of variants were better at clearing HIV infection than others. HIV is a modern-day driving force for human evolution. In certain parts of South Africa, nearly half of women are infected with the virus.
HLAs, produced by the major histocompatibility complex MHC , are by far the most variable region of the human genome, and are an essential part of the immune system. This variant protects people almost completely against HIV and is found in 13 per cent of Europeans.
Ultrasound imaging has found that Bajau people have larger spleens than their neighbours — an adaption which allows them to stay underwater for longer. As Dr Benjamin Hunt from the University of Birmingham puts it , "Our technological and cultural changes alter the strength and composition of the selection pressures within our environment, but selection pressures still exist. So, evolution can happen by different mechanisms like natural selection and genetic drift.
As our environment is always changing, natural selection is always happening. And even if our environment was 'just right' for us, we would evolve anyway! Dr Alywyn Scally, an expert in evolution and genetics from the University of Cambridge, explains : "As long as human reproduction involves randomness and genetic mutation and the laws of the Universe pretty much guarantee that this will always be the case at some level , there will continue to be differences from one generation to the next, meaning that the process of evolution can never be truly halted.
Takeaway: Evolution means change in a population. That includes both easy-to-spot changes to adapt to an environment as well as more subtle, genetic changes.
Scott Solomon , a biologist from the University of Texas in Austin, highlights in his book Future Humans: Inside the Science of Our Continuing Evolution that since — when Gould declared human evolution to have slowed or stopped — it has been possible to sequence the human genome. In the 18 years since then, it has become much faster and cheaper to do so, providing scientists with an unprecedented insight into our recent evolutionary past.
From these data, Solomon explains, researchers have found evidence of natural selection altering genes responsible for our:. One easy-to-understand example of how humans have evolved over recent centuries is how, on some continents, our bodies have adapted to tolerate the most abundant food sources common to that region.
Around 11, years ago , for instance, adult humans were unable to digest lactose — the sugar in milk. As humans in some regions began to rely on dairy farming as a source of nourishment, our bodies adjusted over time to be more able to digest this food, which, previously, was only tolerated by infants and toddlers. We can see evidence of this evolution today because humans in areas with a long tradition of dairy farming — such as Europe — are much more tolerant of lactose in their diet than people in regions that do not have a heritage of dairy farming — such as Asia.
Around 5 percent of people descended from Northern Europeans are lactose intolerant , compared with more than 90 percent of people of East Asian descent. Another source of evidence for recent human evolution cited by biologists is the Framingham Heart Study — the longest-running multigenerational medical study in the world. The Framingham Heart Study is ongoing, and it has become an important repository for scientific data, not only relating to heart disease but also on changing trends in human health overall.
Scientists say that the Framingham data demonstrate that natural selection influenced the Framingham population — reducing height, increasing weight, lowering cholesterol levels, and lowering systolic blood pressures. Importantly, the data do not show that average weight is increasing in Framingham because the women in the study are eating more. Instead, people with genes that affect these traits tend to have more children, meaning that these traits will become more common with subsequent generations.
But the Dutch were not always the tallest people on Earth. The researchers observe that in the midth century, the average height of Dutch soldiers was centimeters, which was well below the average of soldiers from other European countries and tiny compared with American soldiers, who were 5—8 centimeters taller than the average Dutch soldier. But this Goldilocks temperature is swiftly becoming obsolete.
In January, scientists discovered that we are actually way cooler than we think. According to their study , published this January in the journal eLife, the average temperature is much more likely to be The team analyzed medical records from the past years, which included temperature measurements.
They found that, averaged together, the records indicate that there has been a gradual decrease in body temperature of 0. Living comfortably indoors may also have profoundly impacted humans. The shift appears to mean that we need about calories fewer per day to maintain our basic metabolic needs than we did in the past, she says.
And yet Can we get cooler still? Humans are not immune to the effects of natural selection, Joshua Akey , professor at Princeton University, tells Inverse.
Many of the same pressures that we have faced throughout the history of the human race, like pathogens, still exist and threaten our health today.
But our environment has changed dramatically — and that has to have an impact, he says. His favorite example of recent positive selection is FADS2, which is thought to be an important dietary gene.
Different versions of this gene are adaptive in different populations — depending on whether or not they have more meat or plant-based diets , Akey says.
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