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Is it possible that fever is a legacy feature? Like I would expect microbes specialized to the human/mammalian system environment to be able to deal with the r

Is it possible that fever is a legacy feature? Like I would expect microbes specialized to the human/mammalian system environment to be able to deal with the relatively small temperature range of fevers. The selection pressure of fever is pretty well-suited to microbial evolution. It's very incremental, and microbes are known to live in a wide variety of temperatures. It seems much easier to get around than antibiotics, for example, which has of course happened. However, there may have been a time when fever didn't yet exist and therefore the microbes were not yet able to handle it. As the feature evolved in mammals it was successful for a while since it dynamically changed the microbe's environment. If this arms race process was slow enough the feature may be pretty deeply baked into the mammalian genome and persist today despite a relative lack of usefulness compared to the past and even some increased rate of death in the case of high fever.

0cf8612b2e1e 2y ago
I like this idea. This also seems easy to approximate in vitro. Pathogen growth rate at body temp vs pathogen growth rate at fever temp. Are they markedly different? When I have had a fever, it is not a significant absolute temperature change. Seems reasonable that the infection can handle it. It probably always needs to survive room temperate->human temps, so has mechanisms to cover a large gradient.
jjk166 2y ago
Also worth considering natural selection only cares about your genes being passed on, not about your survival. A fever response might be a good way to clear an infection when you're 20 and have yet to pass on your genes, but bad after 50 when evolution expects your grandkids to be able to take care of themselves. It's even possible that an excessive fever that kills you fast and takes the deadly disease along with it, rather than forcing your kin to spend resources caring for you and potentially catching the disease themselves, is evolutionarily beneficial.
- deleted 2y ago
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- pfannkuchen 2y ago
  Ha, that’s interesting. We could look at whether more solitary mammals have less of a fever response. The feature isn’t guaranteed to fall off, of course, but if it did that would be good evidence for this theory. EDIT On the former though I think we’d expect babies to be able to tolerate fever well and they really don’t.
  - bobthepanda 2y ago
    family sizes used to be much larger so evolution was not necessarily predicated on having every child survive, just an average of more than 2.1.
  - jjk166 2y ago
    Babies are deliberately fragile - if there is an issue evolution wants to nip it in the bud early rather than wasting years of resources raising someone who is ultimately not going to reach adulthood anyways. This is part of the reason that mortality in the first year is over 14 times higher than in the second year, even in the developed world with modern medical practices. Evolution doesn't care about babies, they are easily replaceable. Evolution doesn't care about the elderly, they have served their purpose. The most important thing is to keep people in their late teens to early thirties alive at all costs as these are the ones statistically most likely to successfully produce and raise offspring. It is no coincidence that this is also the age where people reach peak physical condition. Nature is brutal, but efficient.
    - maxerickson 2y ago
      Human babies are fragile because of physical limits on gestation time. Lots of mammals stand up and start doing things literal moments after they are birthed.

0cf8612b2e1e 2y ago

I like this idea. This also seems easy to approximate in vitro. Pathogen growth rate at body temp vs pathogen growth rate at fever temp. Are they markedly different? When I have had a fever, it is not a significant absolute temperature change. Seems reasonable that the infection can handle it. It probably always needs to survive room temperate->human temps, so has mechanisms to cover a large gradient.

jjk166 2y ago

Also worth considering natural selection only cares about your genes being passed on, not about your survival. A fever response might be a good way to clear an infection when you're 20 and have yet to pass on your genes, but bad after 50 when evolution expects your grandkids to be able to take care of themselves. It's even possible that an excessive fever that kills you fast and takes the deadly disease along with it, rather than forcing your kin to spend resources caring for you and potentially catching the disease themselves, is evolutionarily beneficial.

deleted 2y ago
[deleted]
pfannkuchen 2y ago
Ha, that’s interesting. We could look at whether more solitary mammals have less of a fever response. The feature isn’t guaranteed to fall off, of course, but if it did that would be good evidence for this theory. EDIT On the former though I think we’d expect babies to be able to tolerate fever well and they really don’t.
- bobthepanda 2y ago
  family sizes used to be much larger so evolution was not necessarily predicated on having every child survive, just an average of more than 2.1.
- jjk166 2y ago
  Babies are deliberately fragile - if there is an issue evolution wants to nip it in the bud early rather than wasting years of resources raising someone who is ultimately not going to reach adulthood anyways. This is part of the reason that mortality in the first year is over 14 times higher than in the second year, even in the developed world with modern medical practices. Evolution doesn't care about babies, they are easily replaceable. Evolution doesn't care about the elderly, they have served their purpose. The most important thing is to keep people in their late teens to early thirties alive at all costs as these are the ones statistically most likely to successfully produce and raise offspring. It is no coincidence that this is also the age where people reach peak physical condition. Nature is brutal, but efficient.
  - maxerickson 2y ago
    Human babies are fragile because of physical limits on gestation time. Lots of mammals stand up and start doing things literal moments after they are birthed.