I got into a big discussion the other day over the use of the term “mutant.” It started over Sherpas. He referred to Sherpas as mutants because they had more red blood cells and were able to breathe better at higher altitudes. I said, yes, that makes them exceptional, but they’re not mutants. There’s a whole population of people who have the more-red-blood-cells gene, and they evolved that way due to evolutionary pressure. But a Sherpa born with four arms, on the other hand, would be a mutant. If those four arms gave him an evolutionary advantage and he had lots of four-armed offspring, after a while they wouldn’t be mutants any more–they would be a population.
Well, my friend’s an economist and I’m a writer. We need expert opinons to settle this dispute. Webster’s 10th Edition says a mutant is “of, or relating to, or produced by mutation,” which is really not helpful. The various definitions of “mutation” only serve to muddy the water further.
So what’s the deal, bio-dopers? Who is a mutant and who isn’t?
(Please note that both of us agreed that the term is value-neutral and not insulting. We weren’t talking bad about Sherpas behind their backs.)
Well, if you interpret the term in the sense of ‘posessing a genetic trait that was originally derived from genetic mutation in the possibly-distant ancestors,’ then the sherpas are probably mutants. Then again, so are the rest of us… based on my understanding of the role mutations are believed to play in Darwinian genetics, most of the traits that distinguish people living today, and the traits that all human beings hold in common, would have originated in a mutation down the line. (In point of fact… has ANYBODY discovered a way that a particular gene or genetic trait could have originated aside from a mutation? Presumably whatever form of protolife first originated in the oceans had a few genes to start with… I think it’s quite possible that everything else was from mutations. )
My dictionary has the definition of a mutation, more or less, as a relatively permanent change in genetics resulting from a physical or biochemical change in DNA or the chromosomes that contain it. I would tend to define a mutant, in terms of living creatures, as either:
1 - a lifeform that shows very different characteristics than its parents as the result of a mutation during its early development or an undiscovered small-scale mutation in the reproductive organs of at least one parent
or
2 - such a lifeform as in definition (1) and any of its descendants who also show or invisibly carry the mutant characteristics.
Definition 2 being the one that leads to all of us being mutants many times over, as above.
Under definition 1, most sherpas are definitely not mutants… except for some freaky sherpa who could breathe without air or something like that.
Hope that was somewhat helpful.
Technically speaking, a mutant would be an organism whose DNA has a sequence that did not come from either parent. That’s not a very useful term when it comes to humans, because on average, if you look hard enough, every human is born with multiple mutations.
Going back to the Sherpa question you had, I’d agree with you. Once a mutation spreads out into the population to a significant degree, you’d call it a polymorphism. Once it becomes the “normal” gene in a population, you’d call it, well, normal.
Polymorphism… hmm… (looks the word up in a few online dictionaries.) I’m not sure that’s quite right.
Suppose there’s a mutant born with six fingers on her right hand… just for an example. She marries, has a few kids, ends up with grandkids, and some portion of those descendents also have six fingers on their right hands. Eventually you have 1% of the population of the planet with eleven fingers total.
The fact that the species now supports two distinct varieties, ten-fingered and eleven-fingered, would be a polymorphism, or an example of polymorphism. But the eleven-fingered peeps aren’t examples of that polymorphism any more than the ten-fingered people are. Polymorphism just means that the species occurs in different varieties (aside from gender.)
You might as well be asking who is tall or who is smart. In the case of the Sherpas, one must differentiate between what is genetic and what is envrionmental. All of us would experiences changes in our blood composition if we lived at high altitude long enough. That’s why some athletes, like cyclists, train at high altitude and/or spend time in hyperpressure chambers. Additionally, one has to ask if the genetic character of Sherpas is differnt in kind or in degree. Do they have a unique gene or just a higher frequncy of a gene that exists in other populations as well?
Further, I’d be skeptical of any claims that “population X” are mutants in the sense that the OP is asking (ie, some unique genetic isolate). One would have to show that all members of “population X” have the given mutation and that no non-members of “population X” have the mutation.
Human populations just haven’t been reproductively isolated for any significant length of time. One can certainly talk about the fequency of a given genetic marker in a given population, but that’s far from being able to call any population “mutants”.
From this discussion, it’s sounding like it’s an obsolete term. Is the term “mutant” ever used in the field of genetics to refer to an individual organism or group of organisms?
Probably “imprecise” is a better characterization than “obsolete”. Like many terms, there is the way scientists use such a term and the way the general public uses it.
There are quite a few biologists/geneticists who frequent this forum, so they can weigh in on whether it’s still used. However, there is nothing unscientific in saying “A mutant strain of lab mice has been developed, which carry the unique gene for…”
Ironically enough, the gene for polydactyly is dominant; it is suppressed in most heterozygotes by various developmental factors.
Mutant in the most relevant sense would mean an organism possesing distinct mutations from the parental lineage that aren’t commonly present in the population at large. In biology, the term “mutant” is used quite often in genetic and developmental research, largely in comparing two strains of organisms (such as Drosophila fruit flies). For instance, in a study comparing lobe eyed Drosophila to wild type (normal) Drosophila, the former would be referred to as the mutant strain while the latter was referred to as the “normal” or “wild type.” In terms of a hard and fast definition that refers to an absolute condition, I don’t think you could find one. As for the Sherpas, they may be mutants compared to the population at large. However, mutant would be a more apt description of a single genetic anomaly, such as Lance Armstrong, than members of a large population who happen to be slightly different from most other populations of people.
This is key. If the Sherpas did possess a unique gene for increased hematocrit, you could refer to them as mutants in a strict technical sense. If however, their increased oxygen capabilities were the result of acclimation or adaptation, then it would be largely incorrect to label them as such.
In today’s (8/25) New York Times, Nicholas D. Kristof has a column entitled, “Building Better Bodies,” and in it he talks about mutations, natural and genetically engineered.
It’s a little scary.
Kristof tells of an obscure breed of mutant cows, Belgian Blues, that “do not have effective myostatin, a substance that curbs muscle growth.” With little to no myostatin in their systems, these cows have bulging muscles with no fat, “like a caricature of Arnold Schwarzenegger.”
Scientists are working to block the production of myostatin in humans as a treatment for muscular dystrophy and the frailty of aging.
Kristof is worried that comes the 2012 or 2016 Olympics all athletes will be engineered to have similarly bizarre musculature. It is quite possible, in fact, that this year will be the last Olympics without genetically engineered athletes.
The June issue of The New England Journal of Medicine, documented a boy with the human version of the Belgian Blues mutation. His genes interfere with myostatin, and “at age 4 he can hold a 3-kilogram dumbbell in each hand with his arms extended.
In fact, there was a very good article in the Sunday NYT Magazine (4 or 5 pages long, as is typical of these articles) a few months back on the subject of genetic engineering of athletes. I can’t remember the exact date, and my search in the NYT archives came up empty handed, but if anyone can get a link to that story, it was ***very ** * interesting.
Are Sherpas “mutants”? Are they genetically distinct from other human populations?
I have a book called Children of Prometheus that discusses the Sherpas at some length (as well as many other people - it’s not all about them). The Sherpas DO have some distinctive traits that occur at high rate in their populations, and very low rates in other populations. I also have another book by a completing different author called Surving the Extremes where Sherpas are also discussed. The author, in that case, is a doctor who has not only climbed Everest multiple times, but has also done research in human adaption at high altitudes.
According to the information in those books, as a matter of fact, they do not have significantly higher levels of red blood cells that other humans fully adapted to the altitudes they live at. So their red blood cell count is environmental, not genetic. However, their hemoglobin and their myoglobin are both slightly better at carrying (hemoglobin) and storing (myoglobin) oxygen than that of other peoples’. During sleep on high mountains, Sherpa lungs maintain a higher rate of breathing, and inhale deeper, than do those of other people, which keeps the body and brain better oxygenated. They tend to sweat less than other people - which prevents dehydration, a real risk at high altitude, and helps keep the body functioning in marginal environments. Above a certain altitude, the average human woman produces smaller babies and tends to deliver prematurely - unless they’re Sherpas. Pregnant Sherpa’s seem able to better provide oxygen to their babies than other people at higher altitudes.
Does that make them mutants? Hmm… I guess it depends on the definition. The other population that’s settled at high altitudes, the natives of the South American Andes, while they likewise show high-altitude adaptions, they show different adaptations - such as higher red blood cell count, physically larger than average hearts and lungs (Sherpa lungs and hearts are similar in size to other humans of their stature), and so forth.
One could just as easily argue that the Swedish are mutants for being so much paler than the average human being (considered globally)
Actually, this proves that they are not mutants, and illustrates several common misconceptions. First is concerning the use of the word “adaptation.” Adaptation in it’s scientific sense refers strictly to alterations in the genotype that allow organisms to better cope with their environment. If Sherpas had adapted, they would be mutants. The proper word to use here is acclimated. Acclimation refers to the alteration of phenotype to allow the organism to deal best with it’s environment, the phenotypic plasticity of an organism responding to changes in the environment. The Sherpas are simply acclimated to the climate, although anyone who spends time at those altitudes would eventually acclimate as well.
Initially, when humans are exposed to high altitudes, the oxygen dissociation curve of their blood shifts to the right. After acclimation, it actually shifts to the left, so that at the lower pressures of O[sub]2[/sub], hemoglobin saturation increases more than it would at sea level (or whatever normal altitude). This is what we see in the Sherpas. See the book in my sig for more information on this. The other consequential physiological modifications are of course the higher hematocrit levels as well as the larger heart and lungs.
Right. In a scientific setting, saying “this mouse/bacteria/human is a mutant!” would be pretty uniformative. You’d say “I’ve isolated a mouse/bacteria/human that’s mutated for this specific trait/gene/locus/allele/whatnot.”
Yes, but no one acclimates as well as the Sherpas.
This is definitely seen in pregnant women in Tibet. Women of Han Chinese descent who have lived their entire lives at the same altitude as Sherpa women nonetheless give birth to their babies earlier, and those children are typically a pound or more lighter than Sherpa babies at birth. Because of this, non-Sherpa women in the higher altitude areas of Tibet are encourage to descend to a lower altitude for pregnancy and birth - it makes for healthier babies.
Go back and actually re-read my post - the Sherpas do NOT have larger lungs and heart - their lungs and heart are the same size as lowland individuals of the same height. It is the natives of the Andes, literally half a world away, who show larger hearts and lungs.
And some Sherpa adaptations, such as reduced sweating and higher rate/deeper breathing at night, are NOT seen even in the best aclimated individuals of low-land ancestry. They ARE seen in Sherpa descendants born and raised in lowland areas, however. These are subtle but inherited differences. It’s like Inuit tending to be short, compact, with limbs and fingers relatively shorter than, say, the Masai, who have inherited tendencies to be tall and lean. All of those groups - Sherpa, Inuit, Masai - show some genetic adaptations to the environment their groups have been living in for a long time. An Inuit adopted by a Masai family and living in Africa is not going to suddenly grow six and a half feet tall and be rail thin - he might be thinner than his cousins in Nunavit, but he will still retain the genetic traits that makes him marginally more adapted to the artic than his adopted family. Likewise, a Masai growing up in Barrow, Alaska will still be tall and relatively thin compared to his neighbors. Sherpas ARE adapted to high places in a way I (as an example) am not, and never will be.
The Sherpa adaptions are not enough to make them another species, but they are enough that it is believed they are the reason there has never been a known case of fatal high-altitude pulmonary or cerebral edema in a Sherpa. Then again, very few Sherpas seem to have a need to spend time on what they call the “big headache” mountains, whereas thousands of lowlanders have pushed themselves past their limits, ignoring little warning signals like extreme pain.
Based on the new evidence you have provided and contrary to what I wrote previously, the Sherpas do not acclimate at all. As a population, they have adapted to be better suited to life at high altitudes. Thus you could argue that they are mutants in some sense. The argument that Swedes are mutants is not as cogent given that they would tan in Brazil. In addition, blonde hair and blue eyes are not traits not normally found in the rest of the population.
However, as I stated previously, someone with a myostatin deficiency gene is better classified as a mutant than an entire group of people with slightly out of the ordinary adaptations. Ultimately, however, the distinction is pretty meaningless.
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