The father of the science of evolutionary medicine, Randolph (Randy) Nesse, has a favorite aphorism: “Medicine without evolution is like engineering without physics.” In the same way that it would be impossible to imagine building the Rosetta spacecraft, sending it 300 million miles to rendezvous with Comet 67P, and successfully deploying the Philae lander, chock-full with sampling instruments, without physics and specifically Newtonian mechanics, it proves similarly impossible, for instance, to get to the root of the horrifying scourge of Alzheimer's disease unless we ask deep and fundamental questions, informed by evolution, about what the alleged poisonous plaques of beta-amyloid protein are doing in the brain in the first place. Is amyloid pure pathology or does it have an vital evolved function in the brain? In this sense, Nesse has frequently claimed that the value of evolution to medicine is that it while it may lead directly to changes in medical practice or indeed to new therapies, more fundamentally its value lies in explaining why things are as they are. That is why Nesse argues that evolutionary biology should be the foundation and cornerstone for medicine as it should be for all biology. This book is an attempt to put yet more flesh on the bones of Nesse’s idea that evolution is the “physics” of medicine. I describe the evolutionary background to seven areas of human disease that are causing deep contemporary medical concern to explain why they exist in the first place—why things are how they are - and how evolution might help us to combat them. I hope it will leave readers with a new respect for evolution as the prime mover for the structure and function of human bodies, even if it does, on occasions, cause them to break down and drives us into ER!

Each chapter is built around the sometimes harrowing but always inspiring personal stories of people trapped in the disease process in question. Each chapter provides an evolutionary explanation for why the disease has come about, and each chapter shows how medical researchers, using powerful insights gained from thinking about disease in an evolution-informed way, are charting our way out of it.

How a modern version of the hygiene hypothesis - called the "old friends" hypothesis - explains why the Western world is riddled with allergic and autoimmune diseases, and what we can do about it.
How evolutionary theory explains why the battle between the different selfish genetic interests of mothers, fathers, and fetuses causes low fertility and can lead to diseases of pregnancy like recurrent pregnancy loss, preeclampsia and gestational diabetes.
What is the relationship between the fact that we have evolved to walk upright - our bipedalism - and a range of orthopedic illnesses?
Creationists have always used the example of the "irreducible complexity" of the human eye as the bedrock of their argument that God designed the human body, not evolution. Modern developmental biology, however, not only strongly rebuts creationism but explains the astonishing secret of how the recipe for eyes actually unfolds from within the developing eye itself, not from external influences, and is leading to cures for eye diseases like retinitis pigmentosa and macular degeneration.
How does cancer evolve so remorselessly towards malignancy that it is proving almost impossible to cure? Cancer evolution can be so extreme and drastic it is forcing us to re-write the rules of evolution by resuscitating a heresy from the 1940s.
Why are coronary arteries evolution's answer to feeding our powerful, muscular hearts with the food and oxygen they need and how has this led to the continuing pandemic of coronary heart disease?
Research into curing Alzheimer's disease has become hopelessly bogged down and billions of dollars have been wasted trying to turn the "amyloid hypothesis" into therapy. Can we use evolutionary thought to better explain why dementia comes about in a way that might lead to fresh hope for a cure?


Friday, 10 April 2015

The Positive Effects of being either Tall or Fat.

Several recent papers provide food for thought about some basic human body measurements and propensity for disease. An NEJM paper by Samani et al has found an inverse relationship between height and susceptibility to coronary artery disease. Short people are more prone to atherosclerosis. 30% of this association was due to low density lipoproteins (bad cholesterol) and triglycerides and the effect was more attenuated in women. The authors point vaguely to some putative shared biological processes that help to determine height and atherosclerosis but otherwise seem at a loss to explain the association. They rule out the idea that smaller people will have smaller bore coronary arteries that might therefore be more susceptible to blockage - women have smaller arteries than men but this does not lead to greater susceptibility.

Meanwhile, in another paper by Gert Stulp et al, in Transactions of the Royal Society, the tallest nation on earth - the Dutch - are examined. Over the last 200 years they have grown, on average, 20 centimetres in height. This effect is shared by all Western nations, but, whereas it appears to have tapered off elsewhere, the Dutch keep growing. They measured reproductive success across three decades between the 1930s and 1960s and found that height was positively linked to greater number of children being born and greater numbers surviving - favouring tall men and average sized women. When they just looked at the women they found that taller women also experienced greater reproductive success.

Finally, one of the most puzzling findings of all. Scientists from the London School of Hygiene and Tropical Medicine report on a huge study which appears to show that people with a high body mass index - obese people - in young to middle age experience a lower rate of dementia as they get older. At highest risk, says the report, are people with a BMI of less than 20 - in the normal weight category but hovering toward underweight. They have a 34% higher chance of dementia as they get older compared with people inside a more normal spectrum of BMI between 20 and 25. But the protective effect of flab goes further. The heavier you get the more the risk of later dementia declines. Clinically very obese people - those with a BMI over 40 - were 29% less likely to get dementia than those of more normal weight. This is a very strange finding which runs diametrically counter to prevailing wisdom. Indeed, one of the up-and-coming theories about Alzheimer's disease is that people who are overweight - clinically obese - perhaps with attendant states of diabetes and cardiovascular problems - perpetually run a high inflammatory condition which can communicate itself to the brain - triggering inflammatory immune reactions there that rapidly kill off neurons. The authors are very confident in their sums but I find this very hard to believe.

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