# How to build the Nocturnal and Diurnal branches of a Humanoid Race? [closed]

I am in the process of building two separate branches of the same race for my science-fantasy setting. One branch The Tribe of Light is Diurnal and The Tribe of Darkness Nocturnal. I have some of their basic traits in mind...

• The Tribe of Light is built for power and endurance and are shorter and heavier built than the Tribe of Darkness.

• The Tribe of Darkness is built for speed and agility and they are taller and slighter built than the tribe of Light.

• Both are omnivorous, possessing keen senses, fleet-footedness and a wiry-strength.

However I find those traits alone unsatisfactory.

I ask what are physical traits common across even different nocturnal and diurnal species respectively. So that I can incorporate at least some of the into the nocturnal and diurnal branches of the humanoid race that I am working on.

• "There is more...." Seems like maybe you meant to write more in this question? It would help, in fact, because as it stands this seems to me perilously close to idea generation. Mar 12, 2016 at 16:35
• Your question is way too broad in its current form. I would suggest getting rid of your whole backstory about the tribe of light and dark, and rather just edit your question so you ask: "What are some physical traits that are common to diurnal and nocturnal species, and how would I apply them to animal/humanoid tribes?" However, even then, your question seems borderline idea generation and off-topic for this site.
– fi12
Mar 12, 2016 at 18:39
– Aify
Mar 12, 2016 at 19:35
• I'm voting to close because the question is too broad. The OP doesn't state whether these are humanoid creatures or not, nor anything about their environment, technology levels or the interactions between these two groups. These could easily be two different species but that isn't stated. Mar 17, 2016 at 17:50
• I really like the question, it's just not answerable without additional information. Mar 17, 2016 at 17:50

Generally speaking, nocturnal creatures have great night vision, while not necessarily very good vision in the light, and vice versa, so that's where I'd start.

Their diets might differ a bit as well, with the diurnal species cultivating the land and eating cereal, and grains, while the nocturnal ones might live in a more underground setting (caves, etc.), and maybe harvest mushrooms and the like, but generally be more predatorial and hunter-gatherer in nature.

This works well with the traits listed above because the diurnal race would use their greater strength and endurance to plow fields, etc., while the nocturnal race would be more suitable as raiders/hunters/scavengers.

AndelROM has stated some very good generalities for nocturnal and diurnal creatures. Consider my answer as a continuation of his answer.

• If the nocturnal tribe never wander out during the daylight, then there should be some difference in the skin coloration too. Nocturnal people should be lacking some coloration pigments and should have paler skin color than the diurnal tribe people.

• The nocturnal people would have at least slightly more refined sense of hearing. Mammals in general were confined night life during the age of dinosaurs (Mesozoic Period) and this resulted in a very advanced form of ear and brain part related to hearing. During the day time, vision gets to slightly suppress other senses.

• If the nocturnal and diurnal difference has been around for at least 30 generations, you might also expect a slight difference in the structure of their legs. Fast running creatures tend to have a longer shin than slower creatures, when the total leg length is equal. Cheetahs, chicken and horses are good examples.

The process by which speciation occurs in a geographic region shared by both populations is called Sympatric Speciation. This is a $\text{"Real Thing"}^{TM}$.

### How it happens

The above Wikipedia article is pretty dense. Here's a relevant snippet"

For example, micro-allopatry, also known as macro-sympatry, is a condition where there are two populations whose ranges overlap completely, but contact between the species is prevented because they occupy completely different ecological niches (such as diurnal vs. nocturnal). This can often be caused by host-specific parasitism [or predation], which causes dispersal to look like a mosaic across the landscape. Micro-allopatry is included as sympatry according to spatial definitions, but, as it does not satisfy panmixia, it is not considered sympatry according to population genetics definitions.

One example of how this might happen is you have a predator with peak activity during a specific time of day (e.g. a sight oriented predator that doesn't tolerate high temperatures might be most active in the morning). Populations of the prey species which are most active outside of the predator's peak activity (e.g. afternoon and dawn) would avoid the predator, have a better chance of survival, and be more likely to pass on their genes.

Since predators adapt to the behavior of prey and vice versa, eventually this will drive one population of the prey species to be active earlier and earlier with the other to be active later and later.

Eventually the two populations of the prey species will not share the same active period and not interact appreciably. Over time this will cause speciation.

### Traits of the two groups

There is no certainty about what traits the two groups will develop. Obviously they'll develop traits that help them survive in the environment their population uses. For example, we don't know whether the nocturnal group will develop low light sensitive, echo location, or improved sense of smell. However, the trait will be consistent with neutral or positive chances of survival. Traits with negative survival potential are quickly weeded out.

To get the specific traits that you want really has little to do with the nocturnal/diurnal speciation and more to do with the specific evolutionary pressures those environments impose on those populations.

Some possibilities for your specific traits:

1. short & heavy - is a good configuration for conserving heat, cold environment? Also good for sprinters
2. tall & wiry - is a good configuration to ridding the body of waste heat. Also a good shape for distance running
3. keen senses - a requirement for spotting prey or avoid predators
4. fleet footedness (over short or long distances?) good for catching prey by running it down or avoiding predators

Some possible traits for nocturnal population:

1. sense tuned for the dark: echo location, low light vision, good sense of smell, one, some, or all the above
2. if, like humans, vitamin D is generated by exposure to the sun, then very low melanin levels will be a requirement (pale skin).
3. you could postulate a tougher skin to deal with brushing against plants and rocks in the dark
4. etc.

Some possible traits for diurnal population

1. ability to see clearly at longer distances
2. darker skin to deal with UV radiation
3. brain better at ranged weaponry (e.g. bow)

Note your body configurations are good for the opposite of what you've proposed. Heavy, short people are better for the cold that we normally associate with night time. But if you could figure out a rationale for why it is cold during the day and warm at night, it still works.

• Why is the reverse-better than what I initially had in mind. The tribes body types were planed around different methods of hunting and combat. I saw the Light-Tribe as more like pursuit-predators, and quite willing to stand their ground and fight. The Dark Tribe were more like Ambush predators, hit hard fast then slink away into the shadows, shying away from direct confrontation. Mar 17, 2016 at 20:33
• My comment on body types solely had to do with temperature regulation. You can write your story so that other factors were more important (as you stated in your comment above). Mar 17, 2016 at 20:41