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In my world I am working on, the species is similar to humans in almost every way except for the following thing things:

  1. They a much more slender
  2. They have very light hair colors such as blond and white
  3. They are 7 feet tall on average
  4. Their toes are longer and better at gripping

What evolutionary history would support this form of human-like creatures?

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You should also have included an introduction to the physics of your world. As in, the type of planet (if it is other than earth), it's atmospheric composition (especially oxygen level), the characteristics of other creatures in the world (are they all lean and large or only humans?) and anything else you have placed differently from earth.

In my answer I am assuming these lean characteristics are limited to humans of the world and other species are as heavy as their counterparts are on earth.

Hair Color

It would have helped if you also stated WHICH hair color was the norm for your people. Anyhow, for generally "light" colored hair, you can use diet preferences. For example, your human(oid) creatures have been eating cereals x, y and z for millenia. These cereals have large quantities of zinc/iron/copper salts in them, which gradually found their way in the hair coloring protein. Similarly if they are also a carnivorous peoples, you can add the same metal salts mention for their meat diets to explain their hair color. Only now those salts are also present in the meats of the animals they hunt and consume. You can also make an interesting grouping of your people by hair color too. People who eat more mutton than vegetables have light brown color hair. People who eat more vegetables have rather grayish hair. People whose diet mainly consists of fish ...

Here I am assuming that by "light hair", you are implying light-colored hair. If you intend to mean "less hair" or "thin hair", please state so clearly.

Height

This can be a result of:

a) Sexual Selection. During the early stages of these human(oid) evolution, taller males were preferred by the females. Taller males having more access to females than shorter males would mean more babies born of taller males which would increase the chance that a taller baby would be born. Repeated over millenia, the general height of these people came out to be 7 feet which is the tallest height supported by their skeletal structure. People can grow taller than that, but they will have problems walking and daily life activities so they are not much preferred by the females. Hence the general height of the individuals is set at 7 feet.

Now comes the very important question of WHY the females preferred tall males? One answer can be that the region where early human(oid)s lived, was grassland area and the grass was really tall. A tall male was more likely to see above this green layer. His and his mate's life would be somewhat easier than a short male, hence females preferred taller ones.

Or/And you can specify that the trees in the area of early evolution stages had their lowest branches sprouting at quite some height. So in times of danger a tall male had better chances of jumping and grabbing a tree branch to save himself and later pull his mate on the tree too.

b) Survival Selection. As in, tall males were more likely to survive in the early stages of these human(oid)s and hence had more chances to reproduce. The difference here is that females don't have a mate preference based on height of males, but taller males are more likely to survive while shorter males died before reaching reproduction age.

Once again you are going to have to throw in reasons of how/why taller males were more likely to survive where shorter males perished.

Were taller males better suited for hunting? Foraging? Was their ability to see for longer distances a key factor?

Slenderness

This is more easier accounted for, than height. We can use two approaches here.

a) Diet. The plants/animals consumed by the human(oid)s contain very little phosphorus. This lack of phosphorus would imply slender, lightweight bones. Lightweight skeleton leads to a thinner muscles and a generally lean build.

You can also use a lack of calcium in their foods but I would rather not prefer that. Calcium is also a key constituent of teeth and you might not want to give them weaker teeth.

b) Survival/Sexual Preference. Lightweight individuals run faster than heavy ones and this can be the key difference between getting caught by a chasing predator and outrunning it till you reach a shelter. Or, for reasons lame and unknown (known only to women), the females could prefer skinnish males over heavier ones.

Longer, Prehensile Toes

This can be easily explained IF your peoples are in early stages of leaving the jungles and settling on the ground. Or maybe they still have to climb trees often for one reason or another. OR maybe they have this super ability to pick up objects with their feet as well as hands, which makes them far more successful engineers/craftsmen than others who can only use their hands for picking up objects.

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    $\begingroup$ I fear you misunderstand sexual selection. Except to the degree that it interferes with basic survival, sexual selection does not need to have any basis in functional fitness. It's just what the other sex likes. Obviously, where sexual selection conflicts with survival the individuals with inappropriate tastes will tend to have their lines terminated, but otherwise there is no obvious reason why sexual selection should choose useful traits. $\endgroup$ – WhatRoughBeast Sep 12 '15 at 5:19
  • $\begingroup$ Nobody is implying that the females always choose useful traits. What I did say is that females of any species have their perks and choices which go a long way determining the characteristics of the population. Nowhere in the answer was it said that longer, leaner physiques, when adapted by females would invariably lead to better offsprings with a greater chance of survival. Females may prefer a physical trait which is in fact negative for the overall survival of the species. Good examples are Eucladoceros and Megaloceros. $\endgroup$ – Youstay Igo Sep 12 '15 at 5:38
  • $\begingroup$ My apologies. You are correct, and I read too hastily. That said, why is sexual selection usually cast in terms of female choice? A female cannot choose what is not offered. Plus, just a nitpick, Gould begs to differ about Megalocerous jstor.org/stable/… and attributes the antler size simply to allometry - "Megaloceros has the predicted antler size for its body size " $\endgroup$ – WhatRoughBeast Sep 12 '15 at 5:53
  • $\begingroup$ If you ask my personal perspective, I would laugh loudly at the notions of sexual selection, survival of the fittest and natural selection. But since these are the norms of today's evolutionary understanding, so I try to explain things in their light. Evolution is a fact, but to think that one (Darwin) has explained the basic rules of evolution ... ah. Well well. Personally I think neither Eucladoceros, nor Megaloceros went extinct due to impractical horns. But since most scholars today think that way, I use it as an argument. $\endgroup$ – Youstay Igo Sep 12 '15 at 6:09
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    $\begingroup$ I think it makes more sense as a 2 step process. First taller males are selected for survival. Females evolve to prefer taller males. Females continue selecting the tallest males in the tribe way past anything necessary. That's how you end up with peacocks $\endgroup$ – Andrey Sep 14 '17 at 14:10
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This species comes from a warmer climate on a smaller earth The changes to normal human physiology aren't that big so it shouldn't be too bad.

They a much more slender - Allen's Rule describes the relationship between surface area to internal volume depending on prevailing climate. Taller, more slender builds tend to work well in warmer climates. Shorter, stockier builds work better in colder climates.

They have very light hair - In humans, lighter hair is correlated with decreased exposure to sunlight. Note the blonde hair of the Scandinavians compared to the dark hair of native Africans.

Skin and hair color by latitude

They are 7 feet tall on average - Giraffes are so tall because they are under evolutionary pressure to reach taller branches that other animals can't reach. So, the species could be under similar pressures to reach higher food sources. Alternatively, spider monkeys have very long arms that they use to swing through the trees.

Spider Monkey

Their toes are longer and better at gripping - If the species is modeled on spider monkeys then extra grippy toes shouldn't be too hard.

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  • $\begingroup$ On the subject of giraffes, it used to be thought that giraffes' long necks evolved due to the need to eat from tree branches etc, or perhaps look for predators. Now many believe that it's mainly sexual selection: the ladies love those long necks, which are used in mating rights battles. en.wikipedia.org/wiki/Giraffe#Neck $\endgroup$ – Max Williams Sep 22 '15 at 15:10
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As you state "the species is similar to humans in almost every way" aside from the 4 physical exceptions I'm going to assume they'd be anatomically analogous to really tall, slender humans. At least the most general terms

I'm not sure if your tall humanoids would be living in forest/jungles based on human variation. Humans living on the African savanna are taller on average than jungle dwellers. My guess is that thick undergrowth and limited visibility in jungles don't favour being tall in the same way it might for a species living primarily on the plains.

One idea that could work is that their planet is a world mainly composed of temperate plains - at a high latitude meaning less sunlight like in Northern Europe which has a lot of fair-haired people - the plains could be broken up by small forested areas that have very tall trees with calorie-rich fruit. A tall, slender humanoid with good grip on their feet would be able to make the nomad circuit between the oases and reach the fruit once there. This might be putting the cart before the horse in terms of evolutionary cause and effect but this stuff can be difficult.

If you want your slender humanoids' upper height limit to be around 8 feet (give or take) then they likely need their home planet to have lower gravity relative to Earth's. Probably similar to Mars' gravity well - which is about 40% of Earth's.

Perhaps they'd have a longer lifespan than humans since larger animals often have a longer period of adolescence during which they reach their full adult size. Kind of like great apes or elephants. It could be that they had a longer life span due the fact that they don't reach reproductive age until the human equivalent of their mid-twenties.

Link to reference article mentioning longer development periods for larger animals - http://www.smithsonianmag.com/science-nature/how-death-played-a-role-in-the-evolution-of-human-height-152527401/?no-ist

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  • $\begingroup$ I kind of need them to Evolve in jungles, but I have other slender sapient creatures that could use this idea $\endgroup$ – TrEs-2b Sep 21 '15 at 22:35
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Numbers 1,3, and 4 could all be the result of a vertical environment, whether that was cliff faces, jungle, or arcology ruins. To be an evolutionary driver, the environment would need to be the primary living area. So possibly a "Jungle World" or the like.

  1. Slenderness could be a result in a lower gravity environment, as well as one that demands a lot of climbing on surfaces that may not support heavier weights.
  2. Lower gravity could also result in a longer body and also be the result of an environment in which an extended reach has more benefit than a more compact frame.
  3. Longer, more prehensile toes, would be the result of needing a good grip for climbing as opposed to merely walking. Footwear would be either non-existent or more like a glove than a boot.

Number 2 could go along with living permanently under a jungle canopy.

  1. This species evolved being exposed to a lower intensity of solar radiation. Their planet is at a distance from the primary, or is primarily overcast, or they live beneath a thick vegetation canopy, or in caves, or primarily in the far northern or southern climes.

Alternately, have you ever read Larry Niven's Integral Trees and Smoke Ring? Zero G living might also lead to such traits.

Initially evolving in a Zero G world would be unlikely, but perhaps a Generation ship with larges open areas of either non-spin or slow-spin, or a caste purposed with maintaining the non-spin and external portions of the ship could reinforce those traits.

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It's simple, they live in a hot environment. You can say the light colored coat reflects more heat. You can also say their planet is of lower gravity. Lower gravity endorses more height and less volume. You can also say there was an evolutionary preassure to be taller since they eat fruit in trees just like Giraffe's. Additionally more height and less volume makes it easier to disperse heat, so you can stick to the hot planet idea.

Source: https://www.health.harvard.edu/staying-healthy/out-in-the-cold

Body type explains some of the varying reactions to cold weather. Taller people tend to get cold faster than shorter people because a larger surface area means more heat loss. And fat's reputation as an insulating material is well deserved, although for warmth during the winter, you want it to be the subcutaneous fat layered under the skin, not the visceral fat that collects in the abdomen.

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