Survival of The Sickest by Sharon Moalem: Research Paper

Survival of the Sickest by Sharon Moalem delves into how certain genetic diseases and illnesses that are present in our gene pool can actually have a positive impact on the survival of humans. Moalem uses examples such as diabetes and supertasting as evidence to support her claims that adaptations that may have been helpful long ago are detrimental now, because of various reasons which she explains. Most of what Moalem says is proved to be correct with one mistake pertaining to the types of diabetes.

Moalem makes two claims about neanderthals that she does not support with sufficient evidence. One of which claims that prehumans and neanderthals interbred, stated in chapter 3, “It’s also possible that humans evolved in multiple places, and that different groups of prehumans and neanderthals even interbred.” (Moalem p. 71) This claim does hold true, humans which migrated out of Africa first interbred with neanderthals in the middle east and continued to do so in most of Eurasia, since all Eurasians are proven to have neanderthal ancestry (about 1.8-2.5% of it). In 2017 a second neanderthal genome was sequenced, from a 52,000 year old fragment of a bone from a female they called Vindija which proved that humans interbred with neanderthals as early as 130,000 to 140,000 years ago, “Thus, in contrast to earlier analyses of chromosome 21 data for the European Neandertals (13), analyses of the full genomes suggest that the putative early modern human gene flow into Neandertals occurred before the divergence of the populations ancestral to the Vindija and Altai Neandertals ~130 to 145 ka.” (Prüfer) The study on both Vindija and the older study on the Altai neanderthals both found evidence that there was significant gene flow between Eurasian prehumans and neanderthals throughout their contact, but researchers also found links between this admixture and certain genes present in some Eurasians, including melanin production and diabetes, both of which Moalem uses as examples in her book. “Using a large clinical cohort, we discovered functional associations between Neanderthal alleles and AMH traits, influencing the skin, the immune system, depression, addiction, and metabolism.”(Simonti) These traits that were advantages to early humans and allowed better chances of survival in the harsh environment of the ice age are now detrimental in our modern environment, proving Moalem correct. A SNP of SLC35F3, which lowered thiamine carriers, could have helped early humans who left Africa deal with changes to their diet regarding carbohydrate metabolism, nowadays though, this adaptation is detrimental to our health because the modern diet includes simpler carbohydrates and less thiamine in foods. This means that while we now demand more thiamine, carriers of this gene have less of it. (Simonti)

The other claim Moalem makes regarding neanderthals is their usage of plants for healing 60,000 years ago in chapter 4. This claim can also be proven true by a recent study done in 2017 on two Belgian neanderthals, one of which, a sickly teenage boy, had some very interesting plaque. It seems he had an infected mouth and there is evidence that he was using a primitive form of penicillin and aspirin to self medicate. The study states, “Our findings support previous suggestions that El Sidrón 1 may have been self-medicating a dental abscess. This was the only individual whose calculus included sequences corresponding to poplar, which contains the natural pain-killer salicylic acid (the active ingredient in aspirin), and also notably contained sequences of the natural antibiotic producing Penicillium from the moulded herbaceous material.”(Weyrich) This definitively proves Moalems claims correct in this regard.

In chapter two when Moalem is describing the three types of diabetes she states that type 3 diabetes is also known as gestational diabetes and that it is a temporary form of diabetes caused by a “hungry baby” that takes the extra sugar in the mother’s blood, “There is also a third type of diabetes, called gestational diabetes” (Moalem p.34) This is incorrect as type 3 diabetes is actually associated with alzheimer disease not gestational diabetes. A study done by a Mayo Clinic neuroscientist stated, “Type 3 diabetes occurs when neurons in the brain become unable to respond to insulin, which is essential for basic tasks, including memory and learning.” (de Widt) Alzheimer's disease is connected to a gene called APOE4 and mice with this gene were found to have lower insulin in older age. Another study also supports this, saying, “While aging is clearly the strongest risk factor for AD, emerging data suggest that T2DM and dyslipidemic states can contribute substantially to the pathogenesis of AD either directly or as cofactors.”(Monte) Since diabetes causes damage to blood vessels in the brain there is a real link to diseases such as alzheimer's and dementia. Insulin resistance can also hinder the brains supply of oxygen, cause accumulation of toxic proteins, and hinders vital brain cell functions. (dlife) Therefore Moalem’s claim about type 3 diabetes is incorrect.

Aversion to bitter foods could have helped early humans avoid consuming poisons that could kill them. Moalem further explains that there are also people who have a heightened sense of taste, called supertasters, and there is research to back this up. As Moalem says, supertasters are linked to their ability to taste propylthiouracil, also called PROP, which give bitter flavors more intensity. “In her laboratory, Bartoshuk and colleagues had noticed non-tasters were relatively homogeneous in response, while the tasters were much more variable, including a subgroup who found PROP to be intensely bitter.” (Hayes) Supertasters have two dominant alleles that allowed them to taste PROP, while tasters had one dominant and one recessive. There is also a third group, nontasters who have two recessive alleles, also called taste blindness, shown in this study, “Where 0.001 = the perceived bitterness of 0.001 M PROP, 0.32N = the perceived saltiness of 0.32 M NaCI, etc. Nontasters have low ratios (___0.4). Those with PROP ratios between 0.4 and 1.2 are considered to be medium tasters and those with PROP ratios >1.2 are considered to be supertasters.”(Bartoshuk) In adults culture can also have an impact on their taste preferences and even “override” their food preferences related to genes. (Mennella) These all show that Moalem was correct in her description of supertasters.

To conclude, most of Moalem’s claims are in fact correct, with the one exception being her description of type 3 diabetes which she calls gestational diabetes when it is diabetes related alzheimer's. But in general Moalem provides correct facts and science to back up what she writes.