Imagine a world where human beings can be organically enhanced to peak physical strength/ speed/ agility and maybe even gain telekinetic abilities to some extent. This enhancement is caused by the (probably painful) bonding of an alien organism to its otherwise perfectly normal human host.

My questions are:
1) Is it biologically plausible at all to imagine that such a creature could gift its host with such powers? Narratively speaking it seems fair to assume that such a pairing would result in reduced lifespan of the host, but would that even have to apply?

2) How would a parasite have to be attached to create such changes in its host? I thought of some bonding to a human's spinal column, but would that do more damage than good?

3) Just for the sake of cool, I imagined these human hosts to have colored eyes - perhaps different sub-species of parasite would result in different eye colors, thus suggesting variations in ability (red eyes are more physically oriented, blue eyes have greater psychic powers, etc). Again, does this make an iota of sense from a biological point of view? Do parasite-host pairings cause such specific physical changes?

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    $\begingroup$ Such creatures exist, but afaik they are called "symbionts", not "parasites". $\endgroup$
    – enkryptor
    Sep 26 '16 at 10:05
  • $\begingroup$ Take a look at leeches, they feed on damages tissues and helps prevent blood clot. If your engineered leeches can secrete an enzyme carrying retrovirus that can reprogram your DNA why not. I thought of attacking the nervous system but it won't work. $\endgroup$
    – user6760
    Sep 26 '16 at 10:40
  • $\begingroup$ There's a Futurama episode about this, called "Parasites Lost" :) $\endgroup$
    – xDaizu
    Sep 26 '16 at 11:35
  • $\begingroup$ It might be easier to answer if you would put one question in, well, question. $\endgroup$
    – Mołot
    Sep 26 '16 at 14:56

The Caddis Larvae already does this in snails, they castrate the host and divert all the body's energy into making a stronger shell which makes the host a much safer home for it.

You can make the host stronger, faster, bigger all you want. It just needs to be at the expense of something else. Maybe reduce the lifespan of the host by making the heart beat twice as hard? That then gives more oxygen to the body for performing other tasks.

The parasites could infect via the eyes, this infection would then be visible and if the parasite is say a fungus, bacteria or a slime-mould, you would then be able to see the build up in the eyes with different genetics causing different colours.


Mitochondria are a precise example of what you need. They exist already. Endosymbiosis

It might be feasible to have a microorganism that enhances strength/endurance, perhaps. Not sure about telekinesis.

  • $\begingroup$ For Endosymbiosis to occur, it would need to be in all of your cells, which would be difficult to achieve. It's one of the main limitations to gene therapy. $\endgroup$
    – Whitehot
    Nov 15 '19 at 12:36

It's mainly plausible:

  1. Physical enhancement is possible if the parasite produce doping and analgesic substances. However, telekinetic abilities is biologically impossible.
  2. In order to inject is doping secretions in the host, the parasite need an access to bloodstream, so any body part near an artery is good.
  3. Some illness can case a change in eye colour like jaundice, but it will most likely conjunctiva colouration rather than a change in iris colour.
  • $\begingroup$ Telekinetic abilities are just these times impossible, in 2077 I can bring my beer with telekineses. ;P $\endgroup$
    – user55267
    Nov 8 '18 at 14:41

1) Absolutely. From a biology perspective, try to imagine the role that an environment has on the process of evolution. Maybe there is an environmental or atmospheric reason that would mean that such an organism would NEED the protection of an advanced being.

Perhaps there is a dominant predator that used to feed on the hosts of (previously docile) guest microorganisms, and their digestive system was previously incompatible with said microorganisms. Rather than adapting to the digestive system of the predator, the organisms instead make the hosts stronger to survive said predators? Energetically, it's easier for a microorganism to adapt to chemical environment rather than restructure its hosts, but this can be explained by predator-prey numerical relations (prey vastly outnumber the predators, so the microorganism favours the more numerous hosts). Energetically speaking, nothing comes for free, so this will have to come at the expense of increased metabolic output. This would accelerate cell death, thus increasing the amount of (imperfect) cell repair in the host (see: ageing) and cause early death by mutations such as cancerous growths and commonly-geriatric diseases such as osteoporosis and dementia.

2) To influence the body's physiological output, the brain is always the way. Altering hormonal output from the pituitary gland and the hypothalamus is the way to get the body to do things it is otherwise incapable of.

3) Alterations of the brain can alter iris colour, or even cause a build-up of minerals in the conjunctiva (the thin layer of skin on the eye). This can happen in people with liver conditions (jaundice of the eyes). This can also be beneficial for the microorganism, as it can alter the host's psychology to favour protecting other hosts of its own kind, maybe altering the brain's release of oxytocin (the love hormone) to be towards similarly-infected hosts (identifiable by the eye alterations).

In nature, role-based colour variation is commonplace, so it is easy to explain these from a sociological perspective. Perhaps these different biological enhancements cause the release of a different salt that gets deposited in the bloodstream, accumulating in the eyes? Transition element salts have a variety of colours (e.g. Copper Sulfate), you can easily look those up.


How this could happen

This is definitely possible. A simple way for a parasite to accomplish most of these changes (aside from telekinesis, which I don't think has any biologically plausible explanation) by modifying the DNA of the host, likely by introducing some retrovirus into the bloodstream to selectively modify the DNA of specific types of stem cells. Especially if the parasite infects children, achieving peak physical state is just a matter of growing larger and producing more muscles.

Even in adults, though, those changes are possible: we stop growing because we're genetically programmed to stop. There's no biological reason why a virus couldn't switch muscle production back on and increase mass to some point beyond what an ordinary human would reach.

Eye color can also change, especially if you want the eyes to become darker. Eye coloration is based predominantly on the amount of melanin in the eyes. Babies are born with pale eyes for this reason. Just as a virus could change your DNA to produce more muscle, a virus could alter the DNA of your eyes to produce more or less pigment. In an adult, if the pigment already exists in the eye, lightening would be a much slower process than darkening, as the existing pigment would take time to naturally degrade, even if the production of melanin suddenly stopped.

How the parasite could attach

The parasite could attach itself just about anywhere. Primarily, it just needs to interface with the circulatory system in order to regulate viral levels in its host's bloodstream. Popular locations for real world parasites would be either in the digestive tract, or under the skin. Parasites are capable of moving about in the body, to some extent, so they can end up just about anywhere. However, tunneling through living tissue is generally bad for the host, so this is probably best kept to a minimum if your goal if physical enhancement.

If your hosts are intentionally infecting themselves over a long period of time, it's likely that they'll select for less painful and less harmful parasite attachments. Subcutaneous parasites might be the best option: they won't cause as many skin lesions if they're under it, while still being removable if they become problematic.

The downside

In terms of downside, the primary question is: why aren't all humans gigantic and muscular? The main reason is probably food. Muscles take energy, and gigantic muscular people take a lot more of it than normal sized people. Neanderthals were substantially more powerful than modern humans, but had to eat four times as much food to sustain that. Parasitized humans would have the same issue: they'd do fine when conditions were good, but die off far more easily in lean years.

They'd also be far more susceptible to cancer. Cancer and growth are two sides of the same coin: if you modify the genome to create more growth, you increase the chance that something goes wrong. This is true even without parasites: large dogs, for example, are more susceptible to cancer than small ones. This issue isn't insurmountable, however. Whales and elephants, for example, have very low rates of cancer formation. Largely, this is due to genetics: both whales and elephants have multiple copies of genes found in humans which prevent cancer formation.

If the parasites have evolved naturally, they're unlikely to make this sort of a modification to their host's genome. Their evolutionary strategy, more or less, is to make hosts that can be very successful in the short term due to their increased physical prowess at the cost of long-term risk due to factors like starvation. It could be selected for in the long term, though.


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