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Body By Darwin
How Evo Shapes Our Health and Transforms Medecine
Jeremy Taylor
More books on Evolution
The difference between modern life expectancy and that of hunter-gatherers is muich greater than the difference between h-gs and wild chimps. And most of that improvement has come in the last 4 generations.
But that doesn't tell the whole story, bc we are getting way more autoimmune diseases (arthritis, MS, IBD and Type 1 diabetes), eczema and asthma, and macular degeneration. Backache, hernias, dodgy hips.
Doctors tend to see the body as a machine which sometimes breaks down and needs to be repaired in the same way a car would be.
But it's not a machine that's been designed to do a certain job. It is a hodge-podge of modules that only 'care' about the owners ability to reproduce. Evo cannot see into the future and desugn for future problems. All it can do is play the cards its dealt.
So the design/machine analogies aren't helpful. Evo works to maximise reproduction, not health, so we are made of bundles of compromises and trade-offs.
Evidence that women least likely to get cancer are ones who come late to first menstruation, quickly have a baby, and then have repeat pregnancies with long breast-feeding.
BRAC 1 and BRAC 2 normally protect against breast cancer, but specific variants lose that. But the fact that such genes still survive, even though they often affect younger women, suggests that they have some protective function. And the indication is that the genes promote both increased fertility and increased mortality. So a typical trade-off where reproductive success valued but long term survival is irrelevant.
The more closely you inspect the human body, the more obvious it becomes that never designed by any expert. Man's repro apparatus - the ridiculous long route the vas deferens takesbetween testes and penis bc it has to loop up and over the uretha. And the vice-like grip the prostate gland has on the uretha as it exits the bladder that makes it so difficult for middle-aged men to pee. And why is a sewage peipe laid right through the middle of the recreation area. The pharynx is used for both breathing and eating, so choking hazard. And of course, the recurrent laryngeal nerve connecting the larynx to the brain. In the giraffe it is 20 feet long.
All up, an argument from Poor Design.
parents of autistic kids noticing that the behaviour problems went away when suffering from a fever.
Humans have two immune systems - the innate immune system, common to all animals, vertebrate and invertibrate, and the adaptive immune system that only vertebrates have. The innate system reacts to any pathogen it detects, by producing inflammation at the infection or injury site. basically it just cordons off the affected area and sends in immune cells to fight. It has no memeory of past events and so offers no long-term protection. The adaptive system uses lymphocytes (type of white blood cell) that produces receptor molecules on its surface in response to antigens detected.
A large range of microbes and fungi needed to be tolerated by human immune systems bc they were ubiquitous, over millions of years, in our food and water. Similarly heminthic parasites needed to be tolerated bc once they got established, they were difficult to dislodge, and any immunological attack would cause disproportionate collateral damage. Over millenia, a state of interdependence seems to have evolved. These commensual organisms needed to regulate our immune systems so that they could live inside us without being attacked, and immune regulation became necessary for us to prevent our immune systems over-reacting.
The problem is that we have cleaned a lot of these organisms, particularly the parasites, from our bodies. The immune system is no longer being held in check, so starts to run wild, leading to the chronic inflamation that is at root of our autoimmune illnesses.
One of the things that first separated humans from apes was the ability to walk upright. Freed our hands to do other things - throw weapons, carry burdens, use tools. No other mammal has developed this, probably bc it comes at great cost. Turns out the vertebrate spine is a very good structure for hanging four limbs off - as long as you use them all for the same purpose, whether a horse running or an ape swinging through the trees. Four-legged animals described as "the bridge that walks" bc spine acts as an arch supported by four piers with legs, chest and abdomen suspended underneath.
We get most of the problems at the base of the spine where it meets the pelvis and the sacrum. These have to support the weight of the upper body, pushing the sacrum down until it narrows the birth canal, with all the childbirth problems that brings.
In a million years or so the foot has had to shift from being a prehensile gripping part to being load-bearing. Ostriches have a foot adapted for running - hteir ankle and foot bones have fused into a single unit, much like the blade runners of paraolympians. But they have had 250 million years of evo to perfect it. Humans have had, at most, 5 million years. We still have 26 bones in our feet bc we are descended from apes who used that flexible structure as basis for a muscular foot good for gripping branches.
Cancers are typically not just one single block of uniformly aberrant cells, but multiple subpopulations of cells with different genetics, different mutations and different patterns of gene activity. But a biopsy usually just works off one sample so doesn't reveal the variability.
If you examine the liver spots on the hands of most middle-aged people, you will find hundreds of cells with mutations disabling an impt gene called P53, which repairs damaged cells, or kills them if beyond repair.
Our skin and bone marrow produce 1013 new cells every day. Even with low mutation rates, we inevitably accumulate mutations.
Cancer treatment constant worry of underdiagnosing benign cancers that turn malignant, or overdiagnosing pre-malignant lesions and wading in with precautionary surgery or chemo that may do more damage than if left alone. The biggest contribution to quality of life is sparing the low risk patients from massive over-intervention. That means not opearting on them, and being confident in that decision, which we can't do at the moment bc no-one wants to take that risk.
Abnormal mitosis now seen as essential part of understanding cancer. Mutations allow chromosomes break in wrong place, or they link to wrong piece. Theory of Punctuated Evo (as opposed to gradual changes leading to new species) not popular, but does seem to apply to tumours. The first cells to grow hog most of the resources. The cancerous cells are by definition more prone to mutate, so multiple genetic combinations are generated. Most will fail, but soem will successfully implant elsewhere in the body.
Chemo has same problem as antibiotics - you're selecting the cells which are resistant to the treatment. Chemo focuses on rapidly dividing cells (which are mostly the cancerous ones) and seems to work for a while. But cells under stress can go dormant, and bc not dividing, don't get hit. As well, the chemo destabilises cells genes and so creates more mutations than there were before.
Two very cheap treatments: dilute bicarb of soda raises pH levels, and seems to combat metstasing cells. Aspirin reduces inflamation, which reduces genetic instability and the production of new blood vessels.
Always told to get off couch and eat healthy to reduce heart attack risk. But recent huge metastudy found that these weren't enough to explain recent increases. Longitudinal studies have shown connection between having tonsils and/or appendix out as child linked to increase haert attack risk. Suggest that bc immune system doesn't grow normally, and that heart diseases due to malfunctions in immune system. We think of artery blocking as a by-product of changes in last 100 years or so - fatty diet and low exercise - but found when exmined historical figures, especially mummies. And while top levels of society would have had a rich diet, they didn't smoke, and they walked everywhere, so got plenty of exercise. But they were exposed to a lot of pathogens, particularly malaria and various intestinal worms.
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