In my story Orcs, humans, and a bunch of other fantasy races live along side each other and i'm curious as to what evolutionary pressures would to a group of divergent hominids to evolve into Orcs?

The basics of my Orcs

  • Can range in height from 161.5 cm (5 ft 3 in) to 188.9 cm (6 ft 2 in) tall

  • Are as intelligent as humans

  • Both men and woman have tusks though men do have larger ones

  • Are two times stronger than humans but spend more time resting (not necessarily sleeping)

  • Have a mildly improved sense of smell

  • can interbreed with humans

  • Have a symbiotic relationship with a type of algae not only allowing the orcs to become much stronger but also giving them their iconic green skin (no longer true)

Note: Magic does not exist in my story

Edit: after some contemplating i decided to remove the algae part for believably and now there gray hope that doesn't change things to much

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    $\begingroup$ I would keep in mind that Orcs in many settings are explicitly the result of Intelligent Design, most famously in LOTR where they were created by Morgoth to wage war against the elves. The Second Apocalypse series also does this really well with its orc analogue; the Sranc, as it goes into some...erm interesting details about how even their neurological system was designed to be ultraviolet, and it was all done with technology rather than magic. $\endgroup$
    – user71781
    Feb 4, 2020 at 21:23
  • $\begingroup$ Does the last bullet point have a typo in it? It's not clear to me. Does the symbiotic relationship make orcs stronger, or make the algae stronger? By what mechanism? The symbiotic relationship is the most unique aspect of your orcs, and it's hard to imagine how it evolved without knowing more about it. $\endgroup$
    – Luke
    Feb 4, 2020 at 21:27
  • $\begingroup$ Is the hominid requirement critical? $\endgroup$
    – Spencer
    Feb 5, 2020 at 0:07
  • $\begingroup$ @Spencer what else do you have in mind? $\endgroup$
    – icewar1908
    Feb 23, 2020 at 20:40
  • $\begingroup$ @NixonCranium: Orcs were not created, since (as IIRC Frodo says to Sam after they leave Cirith Ungol) the dark powers can't create new life, they can only warp (read "genetically engineer") existing life. $\endgroup$
    – jamesqf
    Apr 4, 2020 at 19:40

3 Answers 3


Jungle Giving Way to Savanna

Your orcs share many similarities to humans in that they are both bipedal, roughly the same size and have evolved very high intelligence (for the animal kingdom). So therefore the pressures that made humans will therefore be similar to the ones that made orcs, as this is how convergent evolution works.

The Orcs ancestors were like those of humans; tree dwelling apes that needed to adapt to a changing climate that opened up grasslands. The proto-orcs got their humanoid build and intelligence from these analogous environmental conditions.

But there are notable differences.

Sexual Selection

The tusks of orcs evolved from lower canines that didn’t really serve a particular purpose, but were not harmful. Over time it was selected for sexually much like the antlers of a caribou, which is why they are more pronounced in males but not absent in females.

A Lusher Grassland

The savanna that the orcs evolved in was similar to man’s cradle in the Great Rift Valley, but with some notable differences. The rains were more frequent, leading to taller and more verdant grasses that limited endurance hunting like humans perfected. Therefore orcs evolved a greater sense of smell, in order to detect creatures hiding in the grass as it moved about, and to smell blood, as it couldn’t rely purely on good vision like early human hunters.

An unfortunate reality of the verdant plains for our proto-orcs was the presence of dangerous predators. Orcs evolved their greater strength, better smell and penchant for violence due to the presence of large predators that they needed to fight off at any given moment.

The Algae

This is the only part that’s tricky. Although there are mammals with algae in their fur such as sloths, no mammals have it in their skin and they definitely don’t provide energy. To have an animal take advantage of photosynthesis in its body is an incredible and one in a billion adaptation that is highly advantageous. Orcs got lucky and now get a little more energy from the sun via the microorganism’s photosynthesis producing sugars that the orc can absorb.

  • 5
    $\begingroup$ Early humans were also threatened by large predators, and spread out very widely into environments with other large predators, so that can't explain your violent orcs, but then the OP didn't specify that their orcs were notably more violent. Given how useless photosynthetic skin would be to the orcs, it seems more likely that it would provide some other benefit... perhaps synthesising vitamins, protecting against UV, camouflage, whatever. But not food. $\endgroup$ Feb 4, 2020 at 21:51
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    $\begingroup$ Apparently there is sea slug munching algaes and turning green: en.wikipedia.org/wiki/Elysia_chlorotica All we need is some algae in that lush grassland and some genetic mutation and we are done. $\endgroup$
    – PTwr
    Feb 5, 2020 at 11:47
  • $\begingroup$ @Starfish Prime Fair points. $\endgroup$
    – user71781
    Feb 6, 2020 at 0:43

I think you need to thoroughly create and vet your entire humanoid collection and determine which might be related to which and those that aren't specifically related. In doing this you will define genetic connectors and disconnectors between each humanoid.

In looking at Earth history, you find homosapiens at some juncture mated with neanderthals, so DNA comes down to present day from that join. We do not know origins for those two lines. In your case, you are at that point where both existed and are defining what their relationships are (if any).

Why do your orcs have a symbiotic relationship with algae? Does this mean they also are water-centric where algae typically comes from? What is that relationship like? What benefits do both creatures get out of that?

Other than that single attribute, you have only defined a slightly different human with tusks. I think your other hominids are also important in defining these differences and if you map them out you will find the pressure points you need for your story. Dig into that algae vein and you will find the reason for your orcs.


No reason orcs couldn't still be green if you want - the algae could even be semi-parasitic, since orcs aren't known to be clean. More civilized ones could be grey. I agree, tusks make sense as sexual displays. The chimpanzee comparison is apt, as the difference between their musculature and humans is that they trigger more musculature at once (see hysterical strength) and human muscle is based on maintaining a lot of endurance. Your orcs would be lazy because they had to be. their muscles would burn out trying to do manual labor. They would be good conquerors but poor slaves (think Mongols). They would probably prefer cavalry or hobilar warfare to compensate for limited endurance. More overwhelming surprise attacks, fewer day-long battles.


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