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The Wildlife of Our Bodies
Predators. parasite and Partners That Shape Who We Are Today
Rob Dunn
We have nearly wiped out most of the 'old' enemies like tapeworms, but we are coming down with a whole lot of 'new' ones - Crohn's Disease, inflammatory bowel disease, rheumatoid arthritis, lupus, MS, autism etc. Crohns is a suite of problems associated with attacks by own immune system on your gut - and your immune system always wins. Before WW2 virtually unknown, but now affects 1 in 500 in US. Nobody can find a cause - plenty of correlations.
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Suggestion that could be due to absence of parasites such as tapeworms. The Pronghorn principle. Pronghorns are antelopes capable of extended high speed sprinting and are very flighty. They evolved on American plains where some fearsome predators such as sabertooth tiger and dire wolf. But now that the predators have been killed off, the pronghorn wastes a lot of energy with hair trigger reflexes that are no longer needed. So PP is that (a) all species have genetically based characteristics that relate to the ways they interact with other species and (b) when those other species removed, features become anachronistic or worse.
Ran trial where infected Crohn's patients (extreme cases - patients whose disease had become untreatable by other means) with whipworms from pigs. Pig worms hopefully wouldn't permanently attach to patient's gut. After 24 weeks, all but one of these extreme cases were in remission. Similar trials on IFB, diabetic mice and even MS.
Our way of life has changed, our behaviour has changed, our diet has changed, but our bodies are still running on programs set over 1000's of generations, and still running same old way, unaware that things have changed.
We know our immune system works on two levels - one fights viruses and bacteria, the other deals with larger parasites such as worms. These 2 elements, TH1's and TH2's, have been around for at least 200m years - sharks, fish and mammals all have them. But it turns out there is also a third element to immune system - the peacekeepers. Sometimes a parasite gets established. If the immune system keeps on fighting it, the side effects outweigh the trouble caused by the parasite itself. The body is better off tolerating a certain level of infestation. But if there is no peace to keep, particularly when you're young, the peacekeeper withers. But the two attack systems are still there attacking anything foreign, without a peacekeeper to tell them when to stop.
Also possible that the worms themselves are helping, but producing self-defence hormones which tell immune system to calm down. Or another possibility is that immune system evolved to cope with some of its response being dulled by the parasite's defence system, and so need to over-produce.
Average Western diet gets 3/4 cals from dairy, cereals, simple sugars and alcohol. None of these was available before advent of agriculture. First crops probably too sparse to support and sustain. Select for humans with genes that made easier to digest crops. Most people of West Euro descent have gene which allows adults to digest lactose. Our saliva now contains amylase, which helps break down starches. Some people produce 16x as much amylase, and so digest starch quicker and more efficiently. This was a good thing when food was precious.
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In areas where big cat predators live, approx 3% of monkeys, chimps and apes get predated each year, and that probably applied to early humans as well. (By contrast, cancer kills about 1 in 1000 Americans p.a.) So perhaps for toxiplasma gondi, humans were a viable life cycle, and not a cul de sac.
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