What if we created a race of humans specialized for islands?

Question

I'm creating a fictional universe in which several races exist that are very different from each other due to long term separation. One race is specialized for archipelagos and more specifically, diving. Not super fast swimming, but more of a diving and running type of thing. They will be subjected to several variables which will change their physiology. My question is this: what adaptations might said race develop based on the following variables?

-A gym in which long distance running, gymnastics, and diving equipment can be used

-An environment in which going underwater is required to get food

-A warm, humid climate where it rains often, where excess mass is not necessary

-A culture where intelligence and skill is admired most

-An ancestry of Indonesian, Polynesian, and Australian descent

Give me details. Hair color, eye color, skin color, height, weight, other adaptations, are all welcome.

Answer 1

In order for a given trait to be passed on to future generations, one of two things has to happen: 1. People without the trait die young, or 2. People with the trait outbreed people without it. One way to speed up evolution is to have a society that views diving/running as the ultimate sex symbol. Men and women who aren't in the top 25% of diving/running reproduce at substantially lower rates. Depending on the type of government in your world, you could even have rules about who's allowed to have children based solely on diving/running tests.

As the answer by elemtilas points out, you'd likely end up with improvements to the cardiovascular system. If you're selecting for the best athletes, you might end up with bodies similar to what makes Michael Phelps so fast. Phelps doesn't look very different from other Olympic athletes. If you really want to push the envelope, you could go down the path of paleoanthropologist Matthew Skinner who has a list of the evolutionary adaptations humans might make to adapt to rising sea levels. They include reductions in body hair, changes to the eyes to improve underwater vision, webbed feet, and more.

Answer 2

This was going to be a comment but it got too long.

Polynesian culture is 3,000 years old. That means they spent 3,000 years inhabiting islands and had the opportunity to evolve during that time. In other words, if you want to take a look at unique evolutions that humans would get to specialize for islands, take a look at the Polynesian people. You'll notice that there's a few unique traits, but there's nothing there which is uniquely different from any other human, and they've got no problem with rejoining the gene pool of the rest of the humans. In other words, they're not much of sub-species of humans.

Now, the reason for this is simple - it's because of how amazing intelligence is. Intelligence is the ultimate trump when it comes to evolved advantages and once you get it, you don't need any other evolved advantage because you can make tools. Tools to let you run better, i.e. foot protection. Tools to let you breathe longer, like diving bells, or primitive nets so you don't have to dive at all. Once you start with humans, in other words, nothing new will be evolved or even needed - tools are much faster than evolution, after all.

Yes, given the constraints of the society, the normal selection rules will apply - the strongest and most fit of your people will rise to the top, and if you're looking for a good profile on that, honestly, just look at the Polynesian people. But if you're looking for something new, it's not going to happen because it isn't needed.

Answer 3

They key differences won't be external, so they'll "look like" all the other non-semi-aquatic people in the region.

Consider the ama pearl divers of Japan. They are ordinary Japanese women, except that they exhibit some remarkable cardiovascular physiology due to their avocation. Their lives are spent in diving maybe a hundred times a day to depths of 30 to 60 feet in cold water, traditionally naked or nearly so and without any kind of gear other than a knife and a basket.

Most people can handle depths of 10 to 20 feet without issue. Danger lurks just below! These girls's hearts and vascular systems have adapted to the stresses of diving and remaining submerged for relatively long periods of time while performing vigorous activity.

Notably, they can hold their breaths for two minutes or more. Average person can hold for 3/4 to 1 minute. And when they do it, they aren't diving and swimming and hunting in cold water! During their dives, they become bradycardic. Their heart rates slow to half the normal rate.

Conclusion:
Your semi-aquatic culture will not look sufficiently different from their land lubbing neighbours. Sorry, no fins, no flippers, no webbing, no gills. Since you're base model is Polynesian~Austronesian, they'll probably "look" something like this:

Their differences from other folks will be where it counts: in their lungs and in their hearts!