On my fictional planet humanoid aliens have evolved on one continent, and have since spread around the entire planet, just like humans did on Earth. On Earth humans have since developed slightly different physical attributes, such as skin color, nose size, ear size etc; therefore for the sake of realism I too want this to happen on my planet as well.

But my question is now: How long would a large sustainable group of my humanoid aliens need to live separately from any other group before they developed a notably different appearance than that of another group of humanoids -- provided that they were identical to start with.

Based on these assumptions:

My planet is compatible to Earth, i.e., the same distance from the sun, same temperature, same gravity and same variations in temperature, radiation and other things which may influence the rate of which my humanoids change. Furthermore all the biomes and ecosystems of Earth are present (more or less). I am however both interested in how fast these physical attributes would develop in similar and different biomes.

The humanoid aliens look, behave and reproduce just like humans -- for the sake of simplicity.

With separate I don't mean complete isolation; the different groups may still trade with one another, and there may still be some genetic exchange along the trade routes; I simply mean that the majority of the population -- who presumably live as farmers or fishers -- are never brought into contact with other population groups. (The separation may also be separation by time, since I intend to follow the development of this society through at least ten millennia)

Since I intend to use this world in a computer game (which mostly should be first person) a notably different appearance therefore is one that the player can easily notice even from quite a distance, like for instance a different skin color, or a 2 centimeters different nose size. Therefore -- and because each set of physical attributes will require me to save some data -- I consider any height difference of less than 5 cm, a face feature location difference less than 1 cm or a skin or hair color hue, saturation or brightness difference of less than 0.1 (if all goes from 0 to 1) to not be a notable difference (because it will be within range of the automatically generated random variations).

(BTW) I am interested in how quickly the physical attributes will change, not how they will change

(as response to a comment: in this specific case i care only about genetical physical attributes, not man-made physical differences, such as clothes, tatoos, or any other attempt by my humanoids to alter their appearance)

  • $\begingroup$ by appearance, do you mean genetic, phenotype, or general look including clothes? $\endgroup$
    – Mołot
    Commented Jan 25, 2017 at 10:39
  • $\begingroup$ Diane Dodd did some experiments with fruit flies that 35 generations was all it took for different species to form (species that were incapable of interbreeding). I can't immediately find any information related to dog breeding or animal husbandry that shows how many generations it takes for different characteristics to form, but this could be a good avenue to investigate. $\endgroup$
    – Tim
    Commented Jan 25, 2017 at 15:44
  • $\begingroup$ Editing the question so that it is significantly different is rather impolite, I would say. $\endgroup$
    – AlexP
    Commented Jan 25, 2017 at 16:46

3 Answers 3


Note: The OP has significantly altered the question. This answer is no longer fully relevant. See the section "Physical varieties" for an attempt to answer the OP's new question.


Ethnicity is a socio-cultural attribute. You are speaking about physical anthropological attributes, which, contrary to what Hollywood would have us believe, are not linked to ethnicity.

There are blond Germans and brunette Germans, light-skinned blond Turks with blue eyes and dusky Turks, blond Afghans with blue eyes and stereotypically "central Asian" Afghans, blond Russians and brunette Russians, blond Italians and "Mediterranean" Italians. Mediterranean-looking Italians look exactly like Mediterranean-looking Greeks, and some Turks, and some Spaniards, and many Maltese etc. Blond Italians look just like the stereotypical Germanic. See a massively politically incorrect map at Racial Realities in Europe (Lothrop Stoddard, 1924), chapter 1; more such old-fashioned (and today known to be much less meaningful that their authors thought) maps on Wikipedia.

Ethnicities develop quite quickly (even one century may be enough in the right circumstances, or even less in exceptional circumstances) based on shared language, economical and political links, and geographical proximity. Physical attributes take a lot longer (several millenia) and require a high degree of reproductive isolation.

Physical varieties

To grasp how long it takes for human geographical / physical varieties to form one may consider how stable those varieties are. Forget about skeletons and mummies: we have realistic sculptures, paintings and drawings from Europe, North Africa (mostly Egypt, but also elsewhere), the Levant, Mesopotamia, Persia, China and other places spanning the last three or (in Egypt) four millenia. When we look at those portraits and statues we see people just like us, people showing the same physical types as those which exist today; and yet those portraits and statues are thousands of years old.

The following is a pathetically incomplete list:

  • The Egyptians left many detailed and realistic images and statues, such as the famous bust of Nefertiti, the well-known seated scribe, the pharaoh Menkaure (Mykerinos) and his queen and many many others.

  • The Fayum portaits were made "from the late 1st century BCE or the early 1st century CE onwards" (Wikipedia). They are detailed and realistic; many of them are very beautiful; they show how varied was the population of Helenistic and Roman Egypt. When we look at those 2000 years old portraits we recognize immediately the Mediterranean type, the Levantine type, the North African type; those physical types appear to have changed very little, if at all, during two millenia.

Portrait of a young woman, one of the spectacular Fayum portaits made in the first centuries of the common era.

  • The Romans left many portaits "characterised by unusual realism and the desire to convey images of nature". Among many others, we have excellent images of the emperors, of course, including for example Julius Caesar, Trajan (who was from Iberia), Philip the Arab, Diocletian (from Dalmatia, the eastern coast of the Adriatic), and Maximinus Thrax (from Thracia, modern nothern Greece and Bulgaria).

  • From China we have realistic pictures and statues dating from the 2nd and early 3rd century, such as, of course, the Terracotta Army.

Gentlemen in conversation, Eastern Han Dynasty (25-220 CE) (from Wikipedia)

Since physical types are stable and apparently unchanged over millenia we can obviously assume that they took many millenia to form. Humans are known to be rather promiscuous, with gene flow occuring between populations at the slightest opportunity. Only massive barriers, such as deserts or enourmous distances, can slow the gene flow enough to permit the development of visibly different physical types. Consider the west-to-east gradient in Eurasia: a person from Gaul may be quite different physically from a person from Sichuan; but in the enourmous space in between the physical types intergrade clinally.

  • $\begingroup$ thanks for correcting my error, i will replace the missused word ethnicity with physical attributes $\endgroup$
    – user28547
    Commented Jan 25, 2017 at 16:28
  • $\begingroup$ @Nikolaj: The point is that physical attributes / geographical varieties correlate with ethnicity very very weakly. You simply cannot tell whether a person is a Spaniard, an Algerian, an Italian, a Greek, a Turk, a Syrian, a Lebanese, an Israeli or a Maltese just by looking at them. Conversely, knowing that a person is an Italian will not tell you much about how that person looks. Sure, there are commonly encountered physical types, but one cannot put a lot of confidence in them. $\endgroup$
    – AlexP
    Commented Jan 25, 2017 at 16:52

There isn't a nice short answer to this question. What you are talking about is pretty much subspeciation. No, I'm not trying to start a race discussion or somehow imply that one population is a different species than another population. Please don't come back with comments about how Aztecs and Vikings and Asians can be indistinguishable. I know! People are people.

So back to trying to answer your question. Genetic variations occur for several reasons: predators, food, geographic separation, etc. These variations can occur extremely quickly as in the case of the peppered moth. It went from mostly white colored to mostly black colored in under 100 years! With only one generation per year, this means it took less than 100 generations. There is also mounting evidence of a new species of mosquito forming in the London Underground. The first tunnel opened in 1863, so it is presumably been evolving for only ~150 years. However, I'm fairly certain these mosquitos have several generations of offspring each year so it could be as many as 300, 600, or even 1200 generations of adaptation.

On the other hand, people have lived in Europe for tens of thousands of years, and like AlexP points out, Germans, Turks, Afghans, etc can be indistinguishable based on appearance. The amount of time it will take for your group of aliens to have a generally different appearance (eg, generally Asian looking vs generally African looking) will depend on the evolutionary pressures the group faces. You state it is a large group, so it presumably has a lot of genetic variation (eg, several different families vs. say, Noah and his family). This great variation to start will increase the amount of time it takes for noticeable traits to appear. You also mention that trade occurs between the groups, so surely there will be some genetic mixing that occurs (sailors and brothels!). This will also prevent a lot of genetic variation. So, that leaves you with fewer options for creating noticeable variations. For example, you might use predators that eat a specific portion of your population (like the slow ones or the ones that are predisposed to sex acts with poisonous cacti), or you could give the new population access to a highly nutritious (or even UN-nutritious) food source. Or, you could make the fruit on the trees hang a little higher so those with naturally longer arms are able to feed themselves better (and thus thrive). But at any rate, this will still likely take thousands of years because of the large starting population and the continued contact with other populations.

  • 1
    $\begingroup$ One of the most important factors in human physical variation among geographical populations may be simply genetic drift due to the sparseness of the population in prehistoric times. With few exceptions, the various physical attributes which distinguish varieties seem to be evolutionary neutral. Eye color is neutral. Straight hair vs. curly hair is neutral. Presence or absence of facial hair is neutral in most climates. Skin color hue (western European slightly reddish brown vs. east Asian slightly yellowish brown) is neutral. $\endgroup$
    – AlexP
    Commented Jan 26, 2017 at 1:25

It depends greatly on several factors:

How much variation is present in the gene pool? If they have not been bottlenecked, expect much more than we humans have.

Is their development very plastic? Look at the great difference in dig breeds: something about their genetic structure makes it easy to make such variation. If your species did that, expect radically different breeds in just a few generations.

How isolated are they? You need to prevent the “genetic bucket chain” in order to allow incompatibility to take root.

So, look at the result you want, and fiddle with the factors to allow for that. Point out how/why that’s different from humans, and more like dog breeds or some example of ring species, etc.


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