Friday, June 20, 2014

We Are All Mutants

Over at Scientific American they note that a lot of what people think they know about mutation and genetics they learned from comic books:

[I]n the storyline from the 1980 X-Men comic book “Days of Future Past” penned by Chris Claremont and illustrated by John Byrne and in the movie based on that story, mutants and mutations are presented as things that human society should fear. In the comic book we read that in that bleak dystopian year 2013, “There are three classes of people: ‘H’ for baseline human—clean of mutant genes; ‘A’ for anomalous human—a normal person possessing mutant genetic potential; and ‘M’ for mutant—the bottom of the heap, made pariahs and outcasts by the Mutant Control Act of 1988.”

Of course this fear of mutation in the comics is linked with the fact that real life genetic mutations often are related to disease states like cancer or sickle cell anemia. But genes aren’t just sitting there waiting to give us diseases. As Matt Ridley wrote so eloquently in the 1999 book Genome, “To define genes by the diseases they cause is about as absurd as defining organs of the body by the diseases they get… hearts to cause heart attacks and brains to cause strokes.”

Evolutionary pressures help propagate and sustain some genetic mutations even when they are linked to disease states. Sickle cell anemia is an inherited genetic mutation of the oxygen-carrying hemoglobin protein found in red blood cells. detector during the Paris Summit in X-Men: Days of Future Past, it wouldn’t have just identified Mystique as the The mutation essentially reduces the elasticity of red blood cells, affecting the oxygen binding function and producing the cells’ characteristic curved, sickle shape. These cells have a much shorter life cycle than normal red blood cells, can lead to blockages in small vessels, and generally result in a shortened life span for people with the disorder.

So if it’s an inherited disorder coming from a mutated allele, why has it persisted in the population? A major suggestion is due to the protective effects of sickle cell anemia in regions where the malaria parasite is present. An important part of the life cycle of the malaria plasmodium is spent in red blood cells and the shortened life cycle of red blood cells in sickle cell anemia interrupts development of the parasite. The condition is therefore protective against malaria and defies simple a simple good-bad dichotomy.

If comics adhered more closely to real life, when evil scientist Dr. Bolivar Trask fired up his electronic mutant camouflaged mutant; it would registered all of the humans in the room as well. But it wouldn’t have been able to tell him with certainty whether the mutations they carry are “bad” or “good”. As with the superheroes and supervillains themselves, the answer to that question is more complicated.


PipedreamFarm said...

One could argue that modern medicine removes most of the natural selection concerning diseases that may have been present in humans.

PBurns said...

It might over time, but remember that vaccines and antibiotics have been around for less than 120 years. Natural selection takes a not longer than that, and in fact the antibiotics are falling out of orbit so fast, I expect we may have to find a new way to attack disease sometime in the next 50-100 years, but which time some of the diseases we have been fighting may be extinct (with polio likely to join smallpox and perhaps a few others).

PipedreamFarm said...

When we are talking about natural selection we are talking about diseases that are affected by genetics (cancer, type I diabetes, sickle cell anemia, etc). Unless there is a genetic component (natural immunity) to the diseases being treated with vaccines or antibiotics how would these fall under "natural selection"? Cancer treatments, insulin injections, and hydroxyurea are examples of modern medicine facilitating the propagation of these genetic dieses.

PBurns said...

Polio and smallpox and syphilis are not genetic -- they are an outside force. That said, resistance to these diseases in some populations is genetic, but if resistance has been lowered in recent years, it is not by much, as modern medicine has only been at work for a few generations.

Yes, there is some evidence that sickle cell anemia has a beneficial impact as it seems to improve resistance to Malaria. But sickle cell is a pernicious negative as well. What appears to be going on with sickle cell is a negative tradeoff against another negative tradeoff, with the deal being sufficiently non-beneficial that the vast majority of Africans and Asian (where most Malaria occurs) do not, in fact have sickle-cell anemia.

We do not, in fact, know the causes of cancer. Some causes appear to be genetic, but some are clearly triggered by outside forces (sunlight, toxins, etc.) Has SP50 sunblock lowered our genetic resistance to skin cancer? Not by much. In fact, the fact that we put skin protection on ourselves may be genetically coded -- it's something pigs, elephants and a lot of other animals do. They also eat "natural" medicines to worm themselves, etc. The mind is an evolutionary adaptation, and one can even argue that the Internet fits in there too!

Type I diabetes has a genetic component, but there is more going on there than that. If one in a set of identical twins has Type I diabetes, there is only a one in 2 chance that the other twin will have it. There is some indication Type I diabetes is triggered by some sort of virus, and climate appears to also play a factor, as well as early diet. They are still working on it.

PipedreamFarm said...

It's not that resistance has been lowered by modern medicine, it's that modern medicine is allowing genetically weaker individuals to survive (and possibly thrive) where with natural selection this would not occur.

PBurns said...

I am not sure what "genetically weaker" means.

Most true genetic diseases are recessive, and therefore do not carry any genetic load unless they meet another recessive, and they only "prune out" of the gene pool if the disease becomes self-evident before the age of reproduction and either self-evident (selection bias for mates) or self-limiting (i.e. the carrier is dead before mating).

Dwarfism, albinoism, conjoined twins, mental deficiency, etc, are not treatable in the conventional sense of that word, while a great deal of neonatal problems are not genetic, but simply developmental (lack of oxygen, chemicals consumed during pregnancy, etc.)

Most cancers present quite a bit later than that, and so surgery and chemo have had no impact at all. Childhood leukemia is an exception, but chemotherapy also tends to result in the sterility of the patient. Not sure of the percentage here, but pretty common.

Where modern medicine and disease have intersected most loudly is in the arena of diseases that are spread by air, water, and contact. Here sanitation, antibiotics, insecticides, and vaccines have changed the game massively, and in ways that dwarf all others. Natural resistance to disease may have been lowered very slightly as a consequence, but not by much.

The number of early-presenting treatable genetic diseases is actually quite small I think. I

PipedreamFarm said...

You are correct, most genetically controlled diseases are later onset than procreation; my mistake.