The other major question I’m grappling with is why there is an obesity-elevation gradient.
A guy is going alone through the wilderness, with a solar powered icebox on his back. He crosses a raging river by swimming. He slashes his way through a jungle. He is blasted by sun on an endless desert. It’s been weeks and he has no company at all, save the bleached bones (and ice boxes) of those who did not make it. He climbs a mountain until he finally comes to a cave in the snow. Inside is a man with beard like silvery horsehair, eyes like fire. Very old but fit as a mountain goat.
“O wise sensei, I brought your pizza and ice cream with me. Now tell me the secret of perfect health!”
“It is vely simple”, says the old man while greedily unwrapping a stick of icecream. “Only meet with people who have made a journey such as you youlself just did.”
More prosaically: “It” does not run uphill.
~90% of Earth’s mammalian excreta is produced by humans and their livestock. The livestock especially are immobilized in close quarters and their manure is spread to fields by mechanical means. The manure is often in a fresh condition with viable gut flora present. This means that the fitness of the gut microbiome is independent of the host’s mobility and fitness. They can find plenty of new hosts nearby, and have a good chance of spreading far and wide with tractors. If it can make the host eat x% more, it gains roughly that big an advantage: that much more manure along which it can spread. In state of nature that tactic obviously would not work, it would be much better to have a slim host with good legs.
Selection for larger animals, antibiotic feeding and selection by market forces could also contribute towards more hunger-inducing gut microbes.
Maybe overweight is not the only hit on the host’s well-being. There could be other pathologies by which the mechanised microbes improve their fitness. If this is the case, exposure to bad manure – or biome that derives from it – would be a common cause for both obesity and some other diseases associated with it.
A guy is going alone through the wilderness, with a solar powered icebox on his back. He crosses a raging river by swimming. He slashes his way through a jungle. He is blasted by sun on an endless desert. It’s been weeks and he has no company at all, save the bleached bones (and ice boxes) of those who did not make it. He climbs a mountain until he finally comes to a cave in the snow. Inside is a man with beard like silvery horsehair, eyes like fire. Very old but fit as a mountain goat.
“O wise sensei, I brought your pizza and ice cream with me. Now tell me the secret of perfect health!”
“It is vely simple”, says the old man while greedily unwrapping a stick of icecream. “Only meet with people who have made a journey such as you youlself just did.”
More prosaically: “It” does not run uphill.
~90% of Earth’s mammalian excreta is produced by humans and their livestock. The livestock especially are immobilized in close quarters and their manure is spread to fields by mechanical means. The manure is often in a fresh condition with viable gut flora present. This means that the fitness of the gut microbiome is independent of the host’s mobility and fitness. They can find plenty of new hosts nearby, and have a good chance of spreading far and wide with tractors. If it can make the host eat x% more, it gains roughly that big an advantage: that much more manure along which it can spread. In state of nature that tactic obviously would not work, it would be much better to have a slim host with good legs.
Selection for larger animals, antibiotic feeding and selection by market forces could also contribute towards more hunger-inducing gut microbes.
Maybe overweight is not the only hit on the host’s well-being. There could be other pathologies by which the mechanised microbes improve their fitness. If this is the case, exposure to bad manure – or biome that derives from it – would be a common cause for both obesity and some other diseases associated with it.