...right now, humans are experiencing favorable new mutations:
Apolipoprotein AI-Milano
Heart disease is one of the scourges of industrialized countries. It's the legacy of an evolutionary past which programmed us to crave energy-dense fats, once a rare and valuable source of calories, now a source of clogged arteries. But there's evidence that evolution has the potential to deal with it.
All humans have a gene for a protein called Apolipoprotein AI, which is part of the system that transports cholesterol through the bloodstream. Apo-AI is one of the HDLs, already known to be beneficial because they remove cholesterol from artery walls. But a small community in Italy is known to have a mutant version of this protein, named Apolipoprotein AI-Milano, or Apo-AIM for short. Apo-AIM is even more effective than Apo-AI at removing cholesterol from cells and dissolving arterial plaques, and additionally functions as an antioxidant, preventing some of the damage from inflammation that normally occurs in arteriosclerosis. People with the Apo-AIM gene have significantly lower levels of risk than the general population for heart attack and stroke, and pharmaceutical companies are looking into marketing an artificial version of the protein as a cardioprotective drug.
Increased bone density
One of the genes that governs bone density in human beings is called low-density lipoprotein receptor-related protein 5, or LRP5 for short. Mutations which impair the function of LRP5 are known to cause osteoporosis. But a different kind of mutation can amplify its function, causing one of the most unusual human mutations known.
This mutation was first discovered fortuitously, when a young person from a Midwest family was in a serious car crash from which they walked away with no broken bones. X-rays found that they, as well as other members of the same family, had bones significantly stronger and denser than average. (One doctor who's studied the condition said, "None of those people, ranging in age from 3 to 93, had ever had a broken bone.") In fact, they seem resistant not just to injury, but to normal age-related skeletal degeneration. Some of them have benign bony growths on the roof of their mouths, but other than that, the condition has no side effects...As with Apo-AIM, some drug companies are researching how to use this as the basis for a therapy that could help people with osteoporosis and other skeletal diseases.
Malaria resistance
The classic example of evolutionary change in humans is the hemoglobin mutation named HbS that makes red blood cells take on a curved, sickle-like shape. With one copy, it confers resistance to malaria, but with two copies, it causes the illness of sickle-cell anemia. This is not about that mutation.
As reported in 2001 (see also), Italian researchers studying the population of the African country of Burkina Faso found a protective effect associated with a different variant of hemoglobin, named HbC. People with just one copy of this gene are 29% less likely to get malaria, while people with two copies enjoy a 93% reduction in risk. And this gene variant causes, at worst, a mild anemia, nowhere near as debilitating as sickle-cell disease.
This illustrates an important aspect of favorable mutations. The first mutations are likely to be only somewhat better than the old allele. In the case of Hb-S, the survival rate of children of people having one Hb-S gene is higher than that for children of people with normal genes in malaria areas, but about 25% of their children will still have a severe illness. The new mutation provides almost complete protection with very little illness, a considerable improvement on the first mutation.
Tetrachromatic vision
Most mammals have poor color vision because they have only two kinds of cones, the retinal cells that discriminate different colors of light. Humans, like other primates, have three kinds, the legacy of a past where good color vision for finding ripe, brightly colored fruit was a survival advantage.
The gene for one kind of cone, which responds most strongly to blue, is found on chromosome 7. The two other kinds, which are sensitive to red and green, are both on the X chromosome. Since men have only one X, a mutation which disables either the red or the green gene will produce red-green colorblindness, while women have a backup copy. This explains why this is almost exclusively a male condition.
But here's a question: What happens if a mutation to the red or the green gene, rather than disabling it, shifts the range of colors to which it responds? (The red and green genes arose in just this way, from duplication and divergence of a single ancestral cone gene.)
To a man, this would make no real difference. He'd still have three color receptors, just a different set than the rest of us. But if this happened to one of a woman's cone genes, she'd have the blue, the red and the green on one X chromosome, and a mutated fourth one on the other... which means she'd have four different color receptors. She would be, like birds and turtles, a natural "tetrachromat", theoretically capable of discriminating shades of color the rest of us can't tell apart. (Does this mean she'd see brand-new colors the rest of us could never experience? That's an open question.)
And we have evidence that just this has happened on rare occasions. In one study of color discrimination, at least one woman showed exactly the results we would expect from a true tetrachromat.
Diabetes Resistance
In 2009, researchers at the Broad Institute in Boston, led by geneticist David Altshuler, started recruiting elderly, overweight individuals who, by all accounts, ought to have type 2 diabetes but didn’t. The scientists weren’t looking for genetic mutations that cause diabetes but rather hoping to find mutations that prevent it. Their search paid off; last year, the group reported in Nature Genetics that people who have particular mutations in a gene called SLC30A8 (Solute carrier family 30, member 8) are 65% less likely to get diabetes, even when they have risk factors like obesity (1).
Ability to thrive in low-oxygen environments
Scientists have long known how the people of the Tibetan Plateau, including Nepal’s famous mountain-climbing Sherpa, deal with oxygen levels up to 40% less than those at sea level. Unlike most mountain climbers, whose bodies acclimatize to higher elevations by temporarily boosting hemoglobin—a blood protein that carries oxygen throughout the body—Tibetans have evolved a suite of other biochemical adaptations that let their bodies use oxygen extremely efficiently. That’s good news for the Tibetans, because too much hemoglobin makes the blood harder to pump and likelier to clot, increasing the chances of stroke and heart disease.
But the details of Tibetans’ adaptations have been a mystery. Previous studies have suggested that two genes, EPAS1 (inherited from ancient hominins known as Denisovans) and ELGN1, play roles in reducing hemoglobin and boosting oxygen use.
The team looked for common variants among the Tibetan genomes; they then computed whether those variants likely spread throughout the population by chance or by natural selection. EPAS1 and ELGN1 predictably popped out as strong candidates for evolutionary adaptations, they report today in the Proceedings of the National Academy of Sciences. So did seven additional genes: MTHFR, RAP1A, NEK7, ADH7, FGF10, HLA-DQB1, and HCAR2.
In Tibetans, the ADH7 gene variant is associated with higher weight and BMI scores, which could help the body store energy during particularly lean times on the hardscrabble plateau. The MTHFR variant also helps with nutrient deficiency: It boosts production of the vitamin folate, important for pregnancy and fertility. Folate breaks down when exposed to high levels of UV radiation, so high folate levels would compensate for their increased UV exposure. And HLA-DQB1 belongs to a family of genes that regulates proteins critical to the immune system, particularly important given that extreme living conditions like malnutrition can make people more susceptible to disease, Yang says. What the other four gene variants do is less clear, but they could be an evolutionary response to selective pressures besides high altitude.
The team also used its analysis to pin down a likely date for the split between Tibetans and the closely related Han Chinese population: approximately 4725 years ago, or some 189 generations back.
Lactose Tolerance
Lactose intolerance in adult mammals has a clear evolutionary explanation; the onset of lactose intolerance makes it easy to wean the young. Human beings, however, have taken up the habit of eating milk products. This is not universal; it is something that originated in cultures that kept cattle and goats. In these cultures lactose tolerance had a strong selective value. In the modern world there is a strong correlation between lactose tolerance and having ancestors who lived in cultures that exploited milk as a food.
It should be understood that it was a matter of chance that the lactose tolerance mutation appeared in a group where it was advantageous. It might have been established first by genetic drift within a group which then discovered that they could use milk.
Other Examples:
Nylonase: Nylon Bacteria
Nylonase is an example of beneficial mutation in bacteria. The nylonase bacteria can eat short molecules of nylon (nylon-6). The mutation in these bacteria involves insertion of a single nucleotide in the genetic material. It is estimated that this frameshift mutation might have occurred in the 1940s when nylon was invented. Nylonase can be used in wastewater treatment plants.
Gene Mutation: Almond Trees
Almond seeds from wild species contain amygdalin, a bitter chemical that converts into cyanide inside the human body. According to researchers, consuming wild almonds is fatal. A single gene mutation in wild almond trees resulted in a variety that no longer synthesizes amygdalin. When humans discovered this non-bitter almond species, they cultivated them, which is continued till today.
New Enzyme System
Bacteriologist Barry Hall observed, over a number of months, the evolution of a new, irreducibly complex enzyme system in bacteria. The first mutation modified an existing enzyme to work on the new sugar in the culture. It worked O.K., but wasn't great. As time went on, subsequent mutations improved the enzyme until was very effective. Then, to Hall's surprise, another useful mutation produced a regulator.
Regulators assure that a particular enzyme will be produced only when the specific substance is also present. So now the system is irreducibly complex, requiring the regulator, the enzyme, and the substrate.
And...
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... lots more of those out there. This is just a sampling. Not bad for "damage."
