Book Review: Survival of the Sickest

(Author’s Note: The following review was solicited and is written in accordance with this site’s policy for such reviews.)

Summary: A fast-paced, entertaining, informative account of how past evolution has shaped our current living conditions. Recommended – but with one major caveat.

One of the most common misconceptions about evolution is that it is a steady climb towards perfection, working over time to remove every defect. In fact, natural selection is not a skilled artisan but, to use Richard Dawkins’ phrase, a blind watchmaker. Evolution is a process of tinkering, of incremental change, and of modification of old structures to suit new purposes. Sometimes this can lead to a cul-de-sac of adaptation, where a certain trait or structure is globally suboptimal but locally optimal: it is provably inferior at what it does, and yet natural selection blocks improvement because any change would have to begin by temporarily making things even worse. Evolutionary legacies such as the vestigial appendix, the backwards human retina, and other genetic anachronisms give testament to the way such tradeoffs have shaped our species’ past.

Survival of the Sickest expands on this basic theme to argue for the influence of disease on humanity’s evolution, both inherited disorders and external pathogens. Dr. Moalem’s thesis will probably be familiar to most scientists and informed laypeople, but may come as a shock to the average reader: in some cases, evolution may actually favor the emergence of downright harmful traits and genetic diseases. If a gene variant keeps its possessors healthy and strong in the prime of life and helps them to leave more descendants, but ruthlessly cuts down those same people after they have passed their reproductive ages, there are circumstances under which it will be spread by natural selection. Even mutations that are outright harmful can be selected for, if they offer protection against an even more destructive scourge.

As anyone who’s debated evolution will probably know, the prime example is the gene that produces sickle-shaped red blood cells. When a person has two copies of this gene, it causes the debilitating ailment of sickle-cell anemia. But a person with one copy of this gene enjoys partial protection against malaria, a devastating disease in the tropical regions where the sickle-cell gene first emerged. Dr. Moalem discusses this example at length, as well as a similar genetic disorder called favism, an enzyme deficiency which produces severe anemia if its carrier consumes fava beans. Favism, like the sickle-cell gene, has become extremely common in some populations because it protects against malaria. Interestingly, according to the book, both genes work for the same reason: they make red blood cells more fragile and more stressed, turning them into a hostile environment for the malaria parasite.

Dr. Moalem’s other chief example is hemochromatosis, a genetic disorder that results in toxic amounts of iron accumulating in the body over time. Fortunately there is an effective treatment – old-fashioned bloodletting, which purges the excess iron from the bloodstream. Like favism, hemochromatosis is extremely common in some ethnic groups, and this leads naturally to the question of why. A uniformly harmful disorder would have been culled by natural selection, so by evolutionary thinking, its persistence must have conferred some survival advantage. And as the book argues, there is one. Iron is an essential nutrient not just for us, but for many species of infectious bacteria. When the body is under attack, part of its immune response is to deploy natural chelating proteins that bind to iron in the blood and take it out of circulation. As it turns out, hemochromatosis makes iron more concentrated in some organs, but makes it less concentrated in the disease-fighting white blood cells, making them more effective against deadly pathogens like those that cause tuberculosis and bubonic plague.

All of these are testable and relatively uncontroversial examples, but some of Dr. Moalem’s other arguments I find less convincing. For example, he argues that diabetes may have originated as an adaptive response to an ice age called the Younger Dryas that began suddenly around 13,000 years ago. As evidence, he discusses the remarkable example of the North American wood frog, a tiny animal that survives winter by literally freezing solid, then thawing out and resuming its life no worse for wear when spring comes. The frog accomplishes this by dramatically increasing the sugar concentration in its blood, which acts like a natural antifreeze to prevent destructive ice crystals from forming and rupturing its cell membranes and capillaries. The book’s argument is that diabetes may have originated to play a similar role in humans, offering a partial defense against frostbite in the cold.

This is a clever and intriguing argument, but I am not wholly convinced by it. For one thing, domestic cats and dogs can also get diabetes. Are we to imagine that it evolved in them for similar reasons? And if this thesis is correct, should we not expect to find dramatically higher rates of diabetes among the Inuit and other groups of people who habitually live at arctic latitudes? No such evidence is presented in the book, although if a study were done that found this to be true, it would certainly be powerful evidence in favor of Dr. Moalem’s argument. In the meantime, I remain skeptical.

With all that said, I have to register one fairly major objection to this book. In the final chapter, which is on aging and human birth, Dr. Moalem gives an unqualified endorsement to the “aquatic ape” hypothesis of human origins promulgated by Elaine Morgan. This hypothesis is a notorious piece of pseudoscience, and its supporters repeatedly make glaring errors of fact when arguing in its favor (see the previous link). As far as I am aware, the AAH is dismissed by virtually all qualified evolutionary anthropologists, and rightly so.

I myself can think of one major argument against this hypothesis. Morgan and others promote human hairlessness, subcutaneous fat, downward-pointing nostrils, and other traits as evidence that our species’ ancestors spent a substantial amount of time in an aquatic environment. Yet for all this, human beings lack a particular trait that would be far better evidence of aquatic origin than any of these, and one that we would certainly expect to be widespread if our ancestors evolved in the water: webbed hands. Doubtless, this would greatly improve humans’ swimming ability, which by all accounts is pitiful compared to genuine water-dwelling mammals. It would not be a complex mutation – all it would take is a little less apoptosis during fetal development. Why is this condition not far more common if the AAH is correct? It should be a normal human trait, not the result of rare birth defects.

I do not think Dr. Moalem is ignorant or a bad scientist. Instead, I think this is an example of an all-too-common phenomenon: the scientist who ventures outside their field of expertise and ends up making mistakes that an expert would have been able to point out. However, when he sticks to molecular biology and genetics, his specialty, his arguments are far more cogent and persuasive.

About Adam Lee

Adam Lee is an atheist writer and speaker living in New York City. His new novel, Broken Ring, is available in paperback and e-book. Read his full bio, or follow him on Twitter.

  • http://inthenuts.blogspot.com King Aardvark

    Also with the AAH, why should we lose our hair if we start to swim? Lots of mammals that spend time in the water still have hair, like the otter, though it becomes greasier. Also, we can only hold our breath for ~2 minutes on average, not great by any means. Still, the webbed fingers would probably revert back to non-webbed in a very short amount of time.

    We can become pretty good swimmers, but it’s not natural. I was a competitive swimmer for 9 years in my youth – it takes a lot of work.

    Still, the first part of the book sounds good. Never heard the diabetes hypothesis though. Does he have any research behind this hypothesis (other than the frog analogy) or is it mere speculation?

    Darwin warned against speculation – speculation is well and good, but if you want to be taken seriously, you must have the evidence.

  • lpetrich

    The more usual hypothesis for the origin of diabetes is the “Thrifty Gene Hypothesis”, which states that it is a side effect of metabolism being adjusted for surviving starvation conditions, when it is necessary to retain as much sugar as possible. But when one is well-fed, that adjustment proves maladaptive.

    There’s a similar hypothesis for obesity, that it’s a side effect of trying to survive starvation conditions.

    There’s also the “hygiene hypothesis”, which states that too much cleanliness can cause allergies, as a result of our immune systems not having enough targets.

    More directly parallel to the anti-malaraia adaptations mentioned are Tay-Sachs, which is proposed to be an anti-tuberculosis adaptation, and cystic fibrosis, which is likely an anti-diarrhea adaptation.

    Some microbes, like the cholera bacterium, spread themselves by giving their hosts diarrhea. They make their hosts’ intestinal-lining cells’ chloride-ion molecular pumps much more active, and more chloride ion being pumped out means more water diffusing out by osmosis. This means more fluid for the microbes to spread in. However, diarrhea can cause one to be dehydrated, which is a Bad Thing.

    Cystic fibrosis involves the opposite condition; cells’ chloride-ion pumps are much less active than usual, which produces CF’s other symptoms. This would counteract diarrhea microbes’ attempts to induce diarrhea to make those pumps more active.

    Our beloved and late Allan Glenn had suffered from that condition, sad to say.

  • valhar2000

    How aquatic were the apes?

    I have read descriptions of semi-aquatic ape theories, so to speak, which postutale populations of ape-like creatures that lived on land but frequently swam in the ocean or in lakes. I have never heard of fully aquatic ancestors.

  • valhar2000

    Well, the website Adam linked has answered that particular question.

  • Archi Medez

    Good article.

    “Dr. Moalem discusses this example at length, as well as a similar genetic disorder called favism, an enzyme deficiency which produces severe anemia if its carrier consumes fava beans. Favism, like the sickle-cell gene, has become extremely common in some populations because it protects against malaria.” –Ebonmuse

    A strong piece of evidence to add against the Design argument.

    “I do not think Dr. Moalem is ignorant or a bad scientist. Instead, I think this is an example of an all-too-common phenomenon: the scientist who ventures outside their field of expertise and ends up making mistakes that an expert would have been able to point out.” –Ebonmuse

    Yes. This problem is fairly easy to fix in advance. The author or editor should consult some experts in the appropriate fields before publishing the final product.

  • E.B.

    …human beings lack a particular trait that would be far better evidence of aquatic origin than any of these, and one that we would certainly expect to be widespread if our ancestors evolved in the water: webbed hands.

    My uncle had webbed hands. He always was kind of ape-like too… Is there a connection?!

  • ds

    Humans are the most aquatic ape, right? Duh.

  • http://www.patheos.com/blog/daylightatheism/ Ebonmuse

    Based on a recent comment on Sandwalk, I think I may have to revise my opinion of this book somewhat. It seems that Sharon Moalem is a medical student, not a doctor (I have to say that I got a completely contrary impression from his book, which I suspect is deliberate). He’s also an Orthodox Jewish convert who doubts the ability of unguided evolution to account for the existence of the human species. Worst, if the Sandwalk post is accurate, it appears he’s been censoring critical comments on his own blog.

    While the science in most of his book is still relatively uncontroversial, I have to wonder if the parts I criticized were evidence of a deeper underlying problem, rather than simple missteps. I’m glad I registered skepticism toward his hypothesis of diabetes as an adaptation to cold, which I still find to be dubious, and his endorsement of the aquatic ape hypothesis, which I think is total bunk.

  • http://DiabeticWeightManagement.com/faq Storm

    I’m not really familiar with the aquatic ape theory however for the person who stated that humans are not natural swimmers and should have web fingers — unless I’m mistaken we do have web fingers and toes. Some of us have slight webs and others have more pronounced webbing between our fingers and toes. Unless hoved most animals such as dogs, cats and other mammals also have this webbing. As for being natural swmmers — many women have elected to have their children in a tub with the baby being born under water. Babies, when given the opportunity, are great swimmers. Perhaps not at the level of a fish but then again we’ve been evolving on land for a few million years.

  • Valhar2000

    Storm, check out Ebon’s link to the website about Aquatic Apes. It will answer those concerns quite well.

  • Pat Hadley, MD

    I is interesting to note, that your review unconditionally discounts the “aquatic ape” theory, exactly in the manner of most ivory tower academics. I would like you to re-read that chapter of the book, because Dr. Moalem doesn’t say that the aquatic apes were permanently aquatic, only that their evolution was INFLUENCED by an aquatic or semiaquatic environment. How ele do you explain the shared, specialized traits of subcutaneous fat, downturned nose and neonatal swimming? I would like to ask this revieweer, how much anthropology, biology, evolutionary theory and medicine he or she actually knows?

  • http://www.patheos.com/blog/daylightatheism Ebonmuse

    How ele do you explain the shared, specialized traits of subcutaneous fat, downturned nose and neonatal swimming?

    All mammals have subcutaneous fat; infants from most mammal species can swim; and downward-facing nostrils are a trait common to all catarrhines, not just humans.

    I would like to ask this revieweer, how much anthropology, biology, evolutionary theory and medicine he or she actually knows?

    Given that the aquatic ape hypothesis is rejected by the vast majority of evolutionary biologists, I’d say you’re in a poor position to make arguments from authority.


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