From super-evolved freediving populations of the southern Philippines, to disease resistance as a result of eating human brains (no, really)… Here’s our roundup of three of the most stunning examples of genetic mutations among humans, and a brief exploration of how each has the power to impact the lives of not only whomever it directly affects, but potentially millions of others, too.
When we hear or read about evolution, our minds may cast to Charles Darwin and the animals crawling over the Galapagos islands. However, small instaces of the human species changing and adapting have been recorded in current times, and they’re remarkable.
3 examples of modern-day ‘evolution’
Bajau people of Southeast Asia have a ‘biological scuba tank’ 15,000 years in the making
Freediving is becoming increasingly popular, but the Bajau people of Southeast Asia have been doing it for millennia. And they have the biological scuba tank to prove it.
In 2018, researchers published a paper in the academic journal Cell, in which they reveal that the Bajau, also known as “Sea Nomads”, have significantly larger spleens than neighboring populations. This enlarged organ provides them with an oxygen reservoir for longer, deeper dives.
The Bajau have spleens 50% larger than other nearby populations
The spleen is a fist-sized organ next to the stomach, behind your left ribs. It forms part of the lymphatic system – which plays a role in immune responses. But you can live without it, if necessary, because the liver takes over many of its functions in its absence.
Among other things, it has the ability to make more oxygen available when you hold your breath for a long time. So a healthy spleen is an excellent for freedivers – anyone who dives underwater using only they breath, rather than a scuba tank containing oxygen.
The Bajau people of Southeast Asia have been freediving for millennia. It’s a huge part of what they do, and how they live. There are about a million of them spread across the southern Philippines, Indonesia and Malaysia.
And because of their seafaring, freediving lifestyle, they have evolved to have spleens that are 50% larger than comparable communities living in the same areas as them.
Even members of the Bajau community who don’t dive have extra large spleens
Researchers led by Dr Melissa Ilardo, from the University of Copenhagen, published the results30386-6) of their work with the Bajau in the academic journal Cell.
They found that both divers and non-divers from the Bajau community have unusually large spleens. This means the enlargement isn’t a consequence of regular diving per se. Instead, it is a characteristic the Bajau pass down genetically, from generation to generation. It is hereditary.
“The spleen is a reservoir for oxygenated red blood cells,” Dr Ilardo told the BBC’s Inside Science program, shortly after her team published their research. “So when it contracts, it gives you an oxygen boost. It’s like a biological scuba tank.”
“When they’re diving in the traditional way,” she went on, the Bajau “dive repeatedly for about eight hours a day, spending about 60% of their time underwater. So this could be anything from 30 seconds to several minutes, but they’re diving to depths of over 70m.”
Making use of the mammalian dive response
Anyone who has taken a freediving course will be familiar with the mammalian dive reflex. Dr Ilardo alluded to it during her interview with Inside Science, calling it a “human dive response”.
“You can trigger it by submerging your face in cold water,” she explained. But it’s also important to add that wearing a diving mask limits the extent to which the reflex kicks in. That’s because the mask covers parts of the face that register cold water contact and trigger the response.
All vertebrates possess the response, which combines three independent reflexes. Most obvious is that your heart rate slows down. Next comes vasoconstriction – the tightening of blood vessels – which helps to preserve oxygenated blood for the vital organs. Finally, there’s a contraction of the spleen.
The Bajau diverged genetically from the non-diving Saluan about 15,000 years ago, according to the BBC. During that time, their lifestyle led them to develop this fascinating aquatic adaptation that many non-Bajau freedivers could scarcely dream of.
Cannibal tribe’s genetic mutation may help scientists protect against ‘mad cow’ disease
The DNA of tribes in remote Papua New Guinea (PNG) in Southeast Asia may one day help scientists find a way to protect people from degenerative brain diseases such as Creutzfeldt-Jakob disease. Many people know this particular illness by the moniker ‘mad cow’ disease.
Researchers studying the Fore population of PNG discovered a high incidence of a genetic mutation that protects them from an incurable neurological condition – kuru. People develop kuru after consuming human brain or nervous system tissue containing a particular type of infectious protein.
Practicing cannibalism helped Papua’s Fore tribe develop disease resistance
In the 1950s, Papua New Guinea’s Eastern Highlands province was suffering a terrible, ongoing outbreak of a mysterious disease called kuru. That’s what they called it.
Kuru left entire villages without adult women, according to a recent article in The Guardian. The word “kuru” means something like “shivering”. Those who contracted it – and who couldn’t beat it – lost control of their limbs and bodily functions. Eventually they started to tremor, and died.
It was killing 2% of the Fore tribe per year, and attracted the attention of researchers studying similar diseases. Those who survived kuru passed down the genetic mutation that helped them fight it.
And in 2015, one group of researchers published a paper in the academic journal Nature, arguing that the DNA of the Fore tribe may one day help scientists find a way to protect people from other degenerative diseases, such as the one we call mad cow disease.
How did they test the theory?
The paper refers to the genetic mutation as an “unknown mechanism”. One thing they knew about the variant was that it appeared to stop a specific type of infectious protein from causing other proteins to “fold” in the “wrong” way.
Misfolding eventually leads to cell death.
Researchers replicated the genetic variant they found among the Fore population in laboratory mice. They then infected those mice with either kuru or Creutzfeldt-Jakob. Those mice with the gene variant that matched the Fore population suffered very little.
The gene protected them from the disease’s fatal symptoms. At the time, Dr Jiri Safari, co-director of the National Prion Disease Pathology Surveillance Center, described the finding as a “breakthrough”. However, he added a caveat.
“It’s very possible that this protective polymorphism may not be protective across all prion strains,” ABC News quotes him as saying. Further research required…
Meet the ‘superhuman’ women capable of seeing vivid colors in dull gray stones
12% of women carry a form of color vision deficiency called “anomalous trichomacy”, according to a 2010 research article published by the Journal of Vision.
In a nutshell, it means their retina – the layers of photoreceptor cells in within the eye – contain four types of cone, rather than three. Three is the normal number. Scientists have speculated that these female carriers are “tetrachromatic”, meaning they can see colors other people can’t.
Understanding the eyes
The human eye contains multiple parts, and one of those parts is the retina. The retina has about 120 million “rods” and 6 million “cones”. It’s the cones that give us our color vision; rods detect light.
There are three types of cone cell: red-sensing cones, green-sensing cones and blue-sensing cones. They exist in a rough ratio of 6:3:1, according to the American Academy of Ophtalmology.
Having three types of cones is normal. Other primates like gorillas, orangutans and chimpanzees all have three types of cone, and so do some marsupials. This format is called trichromacy, which literally means “three colors”.
But there is evidence to suggest that some people have four types of cones. Research from 2010 found some 12% of women have a characteristic the researchers call “anomalous trichromacy”.
Are four cones better than three?
According to that paper, speculation that people with four cones in their retina are necessarily “tetrachromatic”, and therefore capable of seeing colors invisible to other people, may not be universally true.
However, there are tests people can take to find out if their retinas have an extra type of cone. Healthline explains that one participant in the 2010 study mentioned above had “perfect tetrachromatic vision”.
She made zero errors in her color matching tests. Her responses were unusually fast. And she’s the first person proven to have tetrachromacy.
And four years later, BBC Future ran a feature on tetrachromatic artist Concetta Antico, describing her as having “superhuman vision”. She describes the realization that she was able to see colors her art pupils were simply unable to see.
Tetrachromat women are capable of seeing shades that others perceive as monotone. What you or I may see as a dull gray, Antico and her ilk might describe in vivid detail.
“The little stones jump out at me with oranges, yellows, greens, blues and pinks,” she says. “I’m kind of shocked when I realize what other people aren’t seeing.”
