Fun With: Genetic Drift

[rhoenix]

This thread originally began with "Genetic Sequencing," but that didn't cover nearly enough of the bases. So:

Premise:
= Humankind gives birth to three new species, one of which was unintentional. Two of the three species are specifically engineered, and have been shown to have 99.98% genetic stability for passing along their genes to the subsequent generation.
= Technological level should be assumed to be about 200-300 years ahead of our present day, and each colony has the full knowledge of their former homeworld, with the tools needed to be on the same technological level, though adapted for their local environment.
= All three colonies should be assumed as having enough local resources to be completely self-sufficient.

Biology/Ecology:
= The first new species is intentionally adapted for an all-water environment, complete with more dense bone structure, more resilience to temperature extremes, articulated fins, gills on the ribcage which feed directly into the lungs (which themselves have been adapted for this dual-purpose of either breathing water or air), a nervous system capable of generating electricity (similar to an electric eel, only with finer control), and greatly enhanced senses.
- The world they now call home is almost entirely a water planet normally obscured by dense cloudcover, with land only found deep underwater, usually from volcanic activity.
- A type of bacteria accidentally brought with the colonists tends to rapidly breed whenever sunlight manages to break through the atmosphere, suffocating anything nearby until an hour or so after the sun manages to break through the cloudcover. As a result, the colonists typically live and work under nighttime conditions.

= The second new species is intentionally adapted to a high-gravity (2x that of Earth's) environment. They are about the same height as the average human, but about twice as wide, and thickly built. They have very dense bones, and a musculature that's well-suited to living in a high gravity environment long-term. They were given polarized vision, and thicker skin that's resistant to harsher environments, including radiation.
- The world is a rocky, mineral-rich one with a thin, but breathable atmosphere.

= The third new species, the unintentional one, developed on a low-gravity environment (0.65G), with no intentional modifications made.
- The world is otherwise similar to Earth, though lacks a moon of its own, and of course has a gravity only 0.65x that of Earth normal. This planet does have a stronger electromagnetic field that what is ordinarily found on planets of similar size and composition, but it was not seen as detrimental enough to halt the efforts of making a long-term colony.

Situation:
- 2000 years pass of uninterrupted growth and development for all three species.


And now, the questions:
1. What will an individual of each species/culture look like in 2000 years?

2. What are likely mutations of each species given their environment, and given that length of time?

3. Would subspecies be likely, and if so, what might they look like?

4. How might each species' genesis on these respective colonies affect their cultural identity as a people? What sociology might arise from these conditions?



Thank you in advance for your thoughts and replies.

[Samuel]

You guilted me into it.

Third species.

1 Lighter bones, weaker muscles, taller bodies and less calcium requirements.

2 There are no likely mutations outside the founder effect.

3 No.

4 No major effects. The world is presumably smaller, but even more geologically active so you would see more natural disasters and a focus on dealing with them.

[rhoenix]

You guilted me into it.

Wasn't meant to be guilt-ridden, but thank you for your response regardless.

Third species.

1 Lighter bones, weaker muscles, taller bodies and less calcium requirements.

2 There are no likely mutations outside the founder effect.

3 No.

4 No major effects. The world is presumably smaller, but even more geologically active so you would see more natural disasters and a focus on dealing with them.

That would make sense for them. The planet is almost the same size of Earth, but all that would still work.

[Samuel]

That would make sense for them. The planet is almost the same size of Earth, but all that would still work.

How? A stronger magnetic field means a larger iron core which would cause a higher gravitational pull on the surface.

First species

complete with more dense bone structure, more resilience to temperature extremes,

Why would they need these? I don't see any usage for the bone structure and water has a high specific heat.

articulated fins, gills on the ribcage which feed directly into the lungs (which themselves have been adapted for this dual-purpose of either breathing water or air),

Why amphibious? If the environment is entirely water, there is no need.

a nervous system capable of generating electricity (similar to an electric eel, only with finer control),

The eel does not use its nervous system to generate electricity. Also, why would an individual need it?

with land only found deep underwater, usually from volcanic activity.

I sense typo.

- A type of bacteria accidentally brought with the colonists tends to rapidly breed whenever sunlight manages to break through the atmosphere, suffocating anything nearby until an hour or so after the sun manages to break through the cloudcover. As a result, the colonists typically live and work under nighttime conditions.

Uh... photosynthetic life produces oxygen.

[rhoenix]

How? A stronger magnetic field means a larger iron core which would cause a higher gravitational pull on the surface.

Not necessarily. Aren't there other mechanisms by which a strong EM field can be produced?

First species

complete with more dense bone structure, more resilience to temperature extremes,

Why would they need these? I don't see any usage for the bone structure and water has a high specific heat.

The bone structure would be for water pressure, and the temperature extremes would be so they could adjust from very cold water (closer to the bottom) to much warmer water with no ill effects.

articulated fins, gills on the ribcage which feed directly into the lungs (which themselves have been adapted for this dual-purpose of either breathing water or air),

Why amphibious? If the environment is entirely water, there is no need.

After speaking with a biologist, I found out that given the basic human form, there simply is no way a body like ours (or similar) could get enough oxygen from the water. We would have to breach the surface for air sooner or later, as whales do - there is simply no way around it.

In fact, having gills on the ribcage wouldn't work in retrospect, simply due to the placement of other necessary things.

Solutions for this would be giving them the capability of storing O2 in their muscle tissue, as whales do. An additional solution would be to replace their hair with long, slender, tendril-like fronds that serve as gills while underwater. Both of those changes would allow them significant time underwater before needing to surface and breathe again.

a nervous system capable of generating electricity (similar to an electric eel, only with finer control),

The eel does not use its nervous system to generate electricity. Also, why would an individual need it?

It was the simplest way I could see, given human physiology, to accomplish the end of allowing them specialized control over generating electricity. In their case, it would be both for defense as well as communication.

with land only found deep underwater, usually from volcanic activity.

I sense typo.

...Where? Most of their structures would float on the surface and plunge downward, as a sort of mirror image to human city skylines today. The only significant land to be found would be deep underwater.

- A type of bacteria accidentally brought with the colonists tends to rapidly breed whenever sunlight manages to break through the atmosphere, suffocating anything nearby until an hour or so after the sun manages to break through the cloudcover. As a result, the colonists typically live and work under nighttime conditions.

Uh... photosynthetic life produces oxygen.

Aside from oxygenating the water when they suddenly bloomed (similar to algal blooms today, but with much more rapid growth), how would this affect anything?

[Manus Celer Dei]

That would make sense for them. The planet is almost the same size of Earth, but all that would still work.

How? A stronger magnetic field means a larger iron core which would cause a higher gravitational pull on the surface.

The rest of the planet could simply be less dense than earth, resulting in the overall mass being less despite being the same size and having a larger iron core. Or as rhoenix says, some other mechanism might be responsible other than the core.

[Samuel]

Not necessarily. Aren't there other mechanisms by which a strong EM field can be produced?

The Earth's magnetic field is produced by the movement of liquid iron in the Earth's core. The only method I can see it to make the entire core molten- the inner core is solid. However, this is due to the extreme pressure at that depth so I don't see how this can be readily manipulated.

The bone structure would be for water pressure,

You don't need strong bones for high pressure underwater. The problem is pressure differences between your insides and the water around you. Having strong bones will not help.

and the temperature extremes would be so they could adjust from very cold water (closer to the bottom) to much warmer water with no ill effects.

http://www.windows.ucar.edu/tour/link=/ ... l&edu=high

How far down are we speaking?

We would have to breach the surface for air sooner or later, as whales do

Given the distance, I recommend having liquid supersaturated with oxygen in convent habitats.

It was the simplest way I could see, given human physiology, to accomplish the end of allowing them specialized control over generating electricity. In their case, it would be both for defense as well as communication.

Communication? Photoluminesince is better for communication.

...Where? Most of their structures would float on the surface and plunge downward, as a sort of mirror image to human city skylines today. The only significant land to be found would be deep underwater.

Ah, I thought you meant the volcanos breached the surface. There will still be undersea mountains though, as long as their is plates.

Aside from oxygenating the water when they suddenly bloomed (similar to algal blooms today, but with much more rapid growth), how would this affect anything?

Algae blooms kill everything because at night they produce CO2. During the day they produce O2 and thus won't kill you.

Note that I am not an expert. If anything I say doesn't sound write feel free to point that out.

The rest of the planet could simply be less dense than earth, resulting in the overall mass being less despite being the same size and having a larger iron core. Or as rhoenix says, some other mechanism might be responsible other than the core.

Except the core is a larger percentage of the planets mass. You'd need to have a larger percentage of the rest of the planet to be less dense.

[rhoenix]

Not necessarily. Aren't there other mechanisms by which a strong EM field can be produced?

The Earth's magnetic field is produced by the movement of liquid iron in the Earth's core. The only method I can see it to make the entire core molten- the inner core is solid. However, this is due to the extreme pressure at that depth so I don't see how this can be readily manipulated.

This is rapidly indicating that I need to spend more time studying planetary data as well as others, so all the pieces fit. I'll shelve this for now until I can be more satisfied with the answer.

(adding reply to Manus Celer Dei here, for continuity:)

The rest of the planet could simply be less dense than earth, resulting in the overall mass being less despite being the same size and having a larger iron core. Or as rhoenix says, some other mechanism might be responsible other than the core.

Except the core is a larger percentage of the planets mass. You'd need to have a larger percentage of the rest of the planet to be less dense.

Correspondingly, yes. This is taking shape as a mineral-poor world as a result of the density and size requirements; the colonists would likely have a nearby moon to mine or something.

The bone structure would be for water pressure,

You don't need strong bones for high pressure underwater. The problem is pressure differences between your insides and the water around you. Having strong bones will not help.

That may be a point. However, the other ulterior motive I have for them is so that they could move and function above water still, even if it's not their preferred environment anymore.

and the temperature extremes would be so they could adjust from very cold water (closer to the bottom) to much warmer water with no ill effects.

http://www.windows.ucar.edu/tour/link=/ ... l&edu=high

How far down are we speaking?

That graph is a good point as well. In that case, temperature extremes aren't a requirement as much as I thought they would be.

We would have to breach the surface for air sooner or later, as whales do

Given the distance, I recommend having liquid supersaturated with oxygen in convent habitats.

That might prove to be more comfortable for them (like breathing pure oxygen might be for us), but I don't want to preclude them being able to breathe air directly.

Because of the points you raised, I'm going to be spending more time on them, as their physiology will dictate their culture in some ways.

It was the simplest way I could see, given human physiology, to accomplish the end of allowing them specialized control over generating electricity. In their case, it would be both for defense as well as communication.

Communication? Photoluminesince is better for communication.

The one and only reason I was hoping to avoid that particular mechanism (communication via photo-luminescence) is because another species I'm planning will be using that extensively, and I didn't want to cause confusion for the reader.

However, if that really is the best way, then the two can be simply described and detailed differently.

Ah, I thought you meant the volcanos breached the surface. There will still be undersea mountains though, as long as their is plates.

Given enough time, they will - but those volcanoes are still tens of thousands of years away from doing so. And yes, they do rest on tectonic plates.

Algae blooms kill everything because at night they produce CO2. During the day they produce O2 and thus won't kill you.

Note that I am not an expert. If anything I say doesn't sound write feel free to point that out.

This particular bacterium was an inspiration from reading other materials on biology. Essentially, they stay completely dormant in water until sunlight hits them - in which case, they drop their lethargy and breed like mad. When there's no more sunlight, they stop breeding If there's no sunlight for more than 6 months, they can die off.

Due to the cloudcover of this water planet, this will obviously create some interesting times.

[Broomstick]

Biology/Ecology:
= The first new species is intentionally adapted for an all-water environment, complete with more dense bone structure, more resilience to temperature extremes, articulated fins, gills on the ribcage which feed directly into the lungs (which themselves have been adapted for this dual-purpose of either breathing water or air), a nervous system capable of generating electricity (similar to an electric eel, only with finer control), and greatly enhanced senses.

Um... electric eels generate electricity with modified muscle tissue, not their nervous systems. Such modified muscle occupies a very high percentage of the fish's body.

I don't think a denser bone structure is necessary.

If you modify them along the lines of cetaceans or seals/walruses that might work better. Keep them air breathers (it works for Earth's marine mammals) but with modifications to better store oxygen. A thick layer of blubber will act as insulation. On Earth the problem of marine mammals is retaining enough heat, not insulating against heat, as water depletes body heat much faster than air. Modify the limbs into flukes for propulsion (you'll probably want to retain fingers of some sort for fine manipulation of objects).

You could engineer gills for supplementary oxygen supply, as noted upthread, with the issue that they will have to surface for an oxygen "boost" on a regular basis. An alternative seldom considered, but that occurs in the real world in some species of turtles is, basically, breathing through one's ass. They would still need periodic surfacing, but it's an alternate mechanism for a supplementary breathing system. Proof that truth is, once again, stranger than fiction.

= The second new species is intentionally adapted to a high-gravity (2x that of Earth's) environment. They are about the same height as the average human, but about twice as wide, and thickly built. They have very dense bones, and a musculature that's well-suited to living in a high gravity environment long-term. They were given polarized vision, and thicker skin that's resistant to harsher environments, including radiation.
- The world is a rocky, mineral-rich one with a thin, but breathable atmosphere.

OK, first of all, not sure they need to be "twice as wide". Their bones will be denser regardless (Earth animals raised in centrifuges develop denser bones even without gene modifications or generations of selection, it's an already present response to loads on the bones) but I'm not sure that making them wider is going to make a difference. Chimpanzees are significantly stronger than human beings, but they aren't "twice as wide". Now, greater lean muscle mass would be an advantage, as would superior insertion points for muscles and tendons.

"Mineral rich" might mean a problem with heavy metals being absorbed from the environment which can significantly impact their health. With a thinner atmosphere they might also find a greater lung capacity handy.

= The third new species, the unintentional one, developed on a low-gravity environment (0.65G), with no intentional modifications made.
- The world is otherwise similar to Earth, though lacks a moon of its own, and of course has a gravity only 0.65x that of Earth normal. This planet does have a stronger electromagnetic field that what is ordinarily found on planets of similar size and composition, but it was not seen as detrimental enough to halt the efforts of making a long-term colony.

Why would a stronger electromagnetic field be a problem?

And now, the questions:
1. What will an individual of each species/culture look like in 2000 years?

First species: sort of a cross between dolphins/walruses and hominids

Second species: highly muscled humans. As being tall would present physiological problems (pumping blood under high gravity does burden the heart, plus the additional mass for a larger body might be problematic in other ways), they will probably be somewhat shorter than the current human average.

Third species: pretty much like us, although they may be more tall and slender than the current human average.

2. What are likely mutations of each species given their environment, and given that length of time?

2000 years is not a lot of time for significant mutations, although it would allow for "founder effects" from a small starting population which could result in some significant genetic drift.

3. Would subspecies be likely, and if so, what might they look like?

See number 2 - not enough time.

4. How might each species' genesis on these respective colonies affect their cultural identity as a people? What sociology might arise from these conditions?

That's quite an open-ended question - I don't think there's just one answer, there's a bunch of ways their societies could go.

[Samuel]

Well, number 2 would obviously focus alot on artifical wombs.

[Broomstick]

Well, number 2 would obviously focus alot on artifical wombs.

Why? I don't see an obvious connection there.

[Samuel]

They are about the same height as the average human, but about twice as wide, and thickly built. They have very dense bones, and a musculature that's well-suited to living in a high gravity environment long-term. They were given polarized vision, and thicker skin that's resistant to harsher environments, including radiation.

If I remember correctly, the process of giving birth involves moving the pelvic bones. Having thicker bones makes this harder.

[Broomstick]

Pelvic bones actually do have a joint. In pregnant women that joint loosens up, allowing the bones to move slightly apart. Bone density should not affect that.

[rhoenix]

Um... electric eels generate electricity with modified muscle tissue, not their nervous systems. Such modified muscle occupies a very high percentage of the fish's body.

There's strike two against this idea. Thank you, though.

I don't think a denser bone structure is necessary.

For the aquatic species, no. You and Samuel are both right on this count.

If you modify them along the lines of cetaceans or seals/walruses that might work better. Keep them air breathers (it works for Earth's marine mammals) but with modifications to better store oxygen. A thick layer of blubber will act as insulation. On Earth the problem of marine mammals is retaining enough heat, not insulating against heat, as water depletes body heat much faster than air. Modify the limbs into flukes for propulsion (you'll probably want to retain fingers of some sort for fine manipulation of objects).

You could engineer gills for supplementary oxygen supply, as noted upthread, with the issue that they will have to surface for an oxygen "boost" on a regular basis. An alternative seldom considered, but that occurs in the real world in some species of turtles is, basically, breathing through one's ass. They would still need periodic surfacing, but it's an alternate mechanism for a supplementary breathing system. Proof that truth is, once again, stranger than fiction.

This ties into my earlier idea about the gill-fronts replacing their hair (yes, I know turtles have anus gills, and I know they work...but call it personal prejudice against ass gills if I can help it), as well as how their musculature will also store oxygen (as whales' do).

(high-g species) OK, first of all, not sure they need to be "twice as wide". Their bones will be denser regardless (Earth animals raised in centrifuges develop denser bones even without gene modifications or generations of selection, it's an already present response to loads on the bones) but I'm not sure that making them wider is going to make a difference. Chimpanzees are significantly stronger than human beings, but they aren't "twice as wide". Now, greater lean muscle mass would be an advantage, as would superior insertion points for muscles and tendons.

Ah, I see what you mean. In this case, they would appear to be a bit shorter and stockier than an average human, but not overly so. That actually works for me.

"Mineral rich" might mean a problem with heavy metals being absorbed from the environment which can significantly impact their health. With a thinner atmosphere they might also find a greater lung capacity handy.

This was my first thought for a wider body, as their chest cavity would be necessarily larger to accommodate for larger lungs.

= The third new species, the unintentional one, developed on a low-gravity environment (0.65G), with no intentional modifications made.
- The world is otherwise similar to Earth, though lacks a moon of its own, and of course has a gravity only 0.65x that of Earth normal. This planet does have a stronger electromagnetic field that what is ordinarily found on planets of similar size and composition, but it was not seen as detrimental enough to halt the efforts of making a long-term colony.

Why would a stronger electromagnetic field be a problem?

That was more a sanity check for DNA stability; I'm not sure if strong EM fields would affect genetic mutation, or affect their longer-term evolution.

And now, the questions:
1. What will an individual of each species/culture look like in 2000 years?

First species: sort of a cross between dolphins/walruses and hominids

Makes sense.

Second species: highly muscled humans. As being tall would present physiological problems (pumping blood under high gravity does burden the heart, plus the additional mass for a larger body might be problematic in other ways), they will probably be somewhat shorter than the current human average.

Makes sense to me.

Third species: pretty much like us, although they may be more tall and slender than the current human average.

With no other effects...which also clears them for the addition of what I had planned for them all along. I'll sanity check low-G flight on normal- or high-G worlds in another thread.

2. What are likely mutations of each species given their environment, and given that length of time?

2000 years is not a lot of time for significant mutations, although it would allow for "founder effects" from a small starting population which could result in some significant genetic drift.

That would be just enough.

4. How might each species' genesis on these respective colonies affect their cultural identity as a people? What sociology might arise from these conditions?

That's quite an open-ended question - I don't think there's just one answer, there's a bunch of ways their societies could go.

With what has been answered, and how, so far - this should serve as a good springboard. You have my thanks for your well-reasoned and thoughtful responses.

[Starglider]

Technological level should be assumed to be about 200-300 years ahead of our present day, and each colony has the full knowledge of their former homeworld, with the tools needed to be on the same technological level, though adapted for their local environment.

2000 years pass of uninterrupted growth and development for all three species.

1. What will an individual of each species/culture look like in 2000 years?

The relatively trivial physical alterations you've made are likely a negligable factor, compared to technological progress and general random cultural evolution. The environmental differences are somewhat more significant, but even still, a highly technological human-derrived culture will be living mostly in cities and will probably be colonising off-planet within a century. In short if you have 4 inhabited planets 250 years from now, you should have thousands of inhabited planets in another two millenia, likely with tens or hundreds of genetically engineered subspecies. Of course the whole thing is rendered irrelevant by transhumanism anyway.

The question would be more sensible if each colony lost their entire technology base, so that they have to redevelop culture from scratch according to local constraints, and so that harsh selection actually causes evolution (although very little in just 2000 years) as opposed to the negligable genetic drift experienced by a civilised society.

2. What are likely mutations of each species given their environment, and given that length of time?

Mutations are random, and not influences by the environment except that mutagens make them more common. Perhaps you mean 'useful mutations', but a technological civilisation does not experience significant selection pressure from the natural environment, so I'd expect their genetic progress to closely track that experienced by the original humans back on earth (not that you will see much change in just 2000 years, even discounting the fact that people are presumably using genetic engineering for a whole host of other reasons).

3. Would subspecies be likely, and if so, what might they look like?

Only if explicitly created by genetic engineering. Whether that will happen depends on cultural factors. Is it accepted to create subspecies for specific job roles? For whimsical or philosophical reasons? Some people will do it just because they can. Again, in a realistic expansionist situation, this will happen anyway as soon as people get out from under the authority of whatever government might be trying to restrict genetic engineering.

4. How might each species' genesis on these respective colonies affect their cultural identity as a people? What sociology might arise from these conditions?

Insufficient detail to usefully speculate, and even if there was a lot of detail, the science of experimental futurist xeno-anthropology hasn't even been invented yet. Practically this is a license to use author fiat; anything that isn't blatantly stupid is ok, accepting that you'll need a huge dose of author fiat to ignore transhumanism and/or accelerating expansion.

Really, it does sound much more like you want earth to be destroyed and all of these colonies reset to the stone age, so they can genuinely take a beating from their environments and be moulded by them.

P.S. Why are you trying to communicate by electric fields, when vocalisations are much longer ranged and require less specialised biology? Sonar is good also, if you can afford the specialised organs and brain areas; an electric field sense is inherently short ranged and only really useful in very cloudy water. A human-scale electric shock mechanism that doesn't fry the user would be a nightmare to bioengineer and would be almost completely useless, due to the horribly short range and the fact that these people have access to technological weapons. Give them sharp claws if they must have a fallback self-defense option, those at least can be useful as tools.

P.P.S. Stronger EM fields do not cause any biological effects, at least not at any strength you could plausibly get from a rocky planet. A significantly weaker field can cause an increased rate of mutation and cancer though, due to more radiation making it to the surface (no Van Allen belts).

[rhoenix]

Really, it does sound much more like you want earth to be destroyed and all of these colonies reset to the stone age, so they can genuinely take a beating from their environments and be moulded by them.

Oh...I have very special plans for Earth. However, the end effect will be that all of these colonies will be completely cut off from the culture, species, and planet that originally made them possible.

P.S. Why are you trying to communicate by electric fields, when vocalisations are much longer ranged and require less specialised biology? Sonar is good also, if you can afford the specialised organs and brain areas; an electric field sense is inherently short ranged and only really useful in very cloudy water. A human-scale electric shock mechanism that doesn't fry the user would be a nightmare to bioengineer and would be almost completely useless, due to the horribly short range and the fact that these people have access to technological weapons. Give them sharp claws if they must have a fallback self-defense option, those at least can be useful as tools.

There is that. An article on echolocation being taught for the blind (humans) recently in Popular Science also made me rethink the necessity of them being able to generate electricity. The one thing that concerned me was how their language would develop as an underwater-based language, or whether they'd have different "dialects" depending on whether they're above or below water.

Samuel's thought of photo-luminescence would work nicely, but as I said, another species I have planned will be making extensive use of it.

(You'd love them - I have yet to see a book give full credit to a fully machine AI-based society; I've a feeling that you'd root for them).

P.P.S. Stronger EM fields do not cause any biological effects, at least not at any strength you could plausibly get from a rocky planet. A significantly weaker field can cause an increased rate of mutation and cancer though, due to more radiation making it to the surface (no Van Allen belts).

Now that's an interesting thought; I might have to use that idea as a Petri dish.

Thank you very much for your reply, Starglider.

[Samuel]

(You'd love them - I have yet to see a book give full credit to a fully machine AI-based society; I've a feeling that you'd root for them).

Will they be a dyson swarm? How are they set up so that they are on equal footing (less than 2 orders of magnitude) with everyone else.

[rhoenix]

(You'd love them - I have yet to see a book give full credit to a fully machine AI-based society; I've a feeling that you'd root for them).

Will they be a dyson swarm? How are they set up so that they are on equal footing (less than 2 orders of magnitude) with everyone else.

Quite honestly, I'd rather not give them or their schtick away just yet. What I will say is that they will have no problem being on "equal footing" with the others. In fact, that will be a major story arc.

Their story primarily will be about their own evolution, and just how close to life their journey takes them.

[Broomstick]

This ties into my earlier idea about the gill-fronts replacing their hair

The problem is that such gills would be enormously vulnerable to damage, and being highly vascularized if they're damaged they're going to bleed a LOT.

With no other effects...which also clears them for the addition of what I had planned for them all along. I'll sanity check low-G flight on normal- or high-G worlds in another thread.

Not sure exactly what you mean by that, but since you intend to start another thread I'll look on it when you do.

[Starglider]

This ties into my earlier idea about the gill-fronts replacing their hair

The problem is that such gills would be enormously vulnerable to damage, and being highly vascularized if they're damaged they're going to bleed a LOT.

Presumably they'd have sphincter muscles in the supplying blood vessels, equivalent to the ones that lizards who can cast their tails use to avoid dying from blood loss. You could probably also cover most of the 'hair' with a 'cowl' flap of skin without losing much effectiveness, if there are openings at the front and back for water to flow through when swimming. Or you could have elaborate bony antler-like structures to keep things away from the gill fronds, that would look cool.

Incidentally the thing about low-g species being tall - this isn't an automatic effect (other than likely a small amount due to the lower g during in development), it will only evolve if there's an advantage to it. Lower gravity simply makes being tall less expensive. Being relatively tall was helpful for early humans because it meant they could see over the savannah grass, but it isn't really that useful in other environments.

[Broomstick]

Being tall has social effects in humans which can affect breeding success. Tall men, in particular, are, on average, seen as more desirable by women - in a context where there are fewer biological penalities for greater height the population may well drift in that direction simply due to sexual selection.

[rhoenix]

The problem is that such gills would be enormously vulnerable to damage, and being highly vascularized if they're damaged they're going to bleed a LOT.

Thank you for pointing this out, as I hadn't even considered this part.

As a reply, one possibility would be to make them very short (about 2-4cm long at most), attached to the scalp, but this would require them to be on the shoulders and upper back to have enough surface area to make a meaningful difference.

Another possibility might be built-in blood sphincters within the gill fronds could act as airlocks do, and simply seal off an affected individual frond section.

With no other effects...which also clears them for the addition of what I had planned for them all along. I'll sanity check low-G flight on normal- or high-G worlds in another thread.

Not sure exactly what you mean by that, but since you intend to start another thread I'll look on it when you do.

I was thinking out loud with this one; my apologies for being vague. However, it does have to do with flight mechanics under different conditions, so I'd be glad of your thoughts. I'll make the other thread for it now.

[Memnon]

Being tall has social effects in humans which can affect breeding success. Tall men, in particular, are, on average, seen as more desirable by women - in a context where there are fewer biological penalities for greater height the population may well drift in that direction simply due to sexual selection.

Sexual selection has, and will, change, of course. For instance, in ancient rome, desirable penis size was the opposite of what it is today.
(The most direct example I could think of)
Over the short time that modern humans have been here, the selection has changed - it's likely that, in two thousand years, theirs will change from our preferences.

Also, about the bacterium - I think what you're trying to get at there is cultural eutrophication, in which algae blooms where there's a lot of nutrients. It was mentioned that the algae produce CO2 at night - this is true, but the major source of the asphyxiation is the use of most of the oxygen by the primary-level consumers which feed on the algae. To get this kind of effect on your water world, I would expect there to be lots of nutrients in the water, and for the one species to possibly be omnivorous - feeding on each other once the sun goes away, or something?

[rhoenix]

Sexual selection has, and will, change, of course. For instance, in ancient rome, desirable penis size was the opposite of what it is today.
(The most direct example I could think of)

...What? Please explain this one. Not to drag the discussion downward, but this made absolutely no sense.

Over the short time that modern humans have been here, the selection has changed - it's likely that, in two thousand years, theirs will change from our preferences.

Also, about the bacterium - I think what you're trying to get at there is cultural eutrophication, in which algae blooms where there's a lot of nutrients. It was mentioned that the algae produce CO2 at night - this is true, but the major source of the asphyxiation is the use of most of the oxygen by the primary-level consumers which feed on the algae. To get this kind of effect on your water world, I would expect there to be lots of nutrients in the water, and for the one species to possibly be omnivorous - feeding on each other once the sun goes away, or something?

They feed on carbon and calcium to grow, and they have little problem extracting the two through osmosis. Like through skin, for instance. Getting caught in a bloom is...bad. Very very bad.

[Memnon]

Sexual selection has, and will, change, of course. For instance, in ancient rome, desirable penis size was the opposite of what it is today.
(The most direct example I could think of)

...What? Please explain this one. Not to drag the discussion downward, but this made absolutely no sense.

From wikipedia's article on itwikipedia's:

The weekly Q&A column "The Straight Dope" deduces, based on pornographic Greek art work and Dover's aforementioned study, that in ancient Greece an uncircumcised and small penis was culturally seen as desirable in a man, whereas a bigger or circumcised penis was viewed as comical or grotesque (at least in the high-brow view), usually being found on "fertility gods, half-animal critters such as satyrs, ugly old men, and barbarians."[17]

Also, I seem to recall that mosaics were found in Pompeii parodying the large penis. However, wikipedia mentions something to the opposite effect. Anyways, that's the reasoning behind that.

Over the short time that modern humans have been here, the selection has changed - it's likely that, in two thousand years, theirs will change from our preferences.

Also, about the bacterium - I think what you're trying to get at there is cultural eutrophication, in which algae blooms where there's a lot of nutrients. It was mentioned that the algae produce CO2 at night - this is true, but the major source of the asphyxiation is the use of most of the oxygen by the primary-level consumers which feed on the algae. To get this kind of effect on your water world, I would expect there to be lots of nutrients in the water, and for the one species to possibly be omnivorous - feeding on each other once the sun goes away, or something?

They feed on carbon and calcium to grow, and they have little problem extracting the two through osmosis. Like through skin, for instance. Getting caught in a bloom is...bad. Very very bad.

Through osmosis? Humans as they are now have the (mostly) waterproof epidermis. Why would a water-engineered human have worse protection? No, the main problem would be at the openings and mucous membranes like the mouth, nose, etc. The only reason I see for the microorganism to need calcium is if there's a shortage of it in the water - for instance, there isn't such a deficit in Earth's water unless there's some pH imbalance. I'm not an expert on that, though.
Also - it's not like carbon and calcium are just... _there_ in the form that the organism needs. They'll be locked up in various molecular structures, which aren't just going to be able to be magicked away via osmosis. Somehow, you have to dissolve the structure (not necessarily the molecular structure - they could have enzymes which modify the molecular structure). Bones, for instance, are surrounded by less calcium-rich tissue, but the calcium doesn't somehow osmose away. Remember that osmosis is a passive process.