I think it is very easy to imagine a local minima in which evolution would be stuck. Making a membrane far too hard to pierce could starve a predator into extinction instead of making it evolve.
If you reach a point where one organism developed enough mechanisms to resist simple predators and that their advanced predators die out, I think it would be impossible for evolution to get out of that dead end. I am not sure that getting unstuck is a universal feature of life.
Emergence of sexual reproduction, of multi-cellular organisms, are all very weird phenomenon that I think are risky to take for granted.
I mean, it feels like playing Conway's game of life: Often, when you start a random one, it all dies out. It often gets stuck in a position where just a few things vibrates. Some last longer. Others go on forever but are rarer.
My intuition (which can be dismissed without argument) is that life is similar: if the conditions are right, it may lead to emergent evolutionary behaviors that eventually can lead to intelligent life, but that's not the most common outcome.
> If you reach a point where one organism developed enough mechanisms to resist simple predators and that their advanced predators die out, I think it would be impossible for evolution to get out of that dead end.
If all the predators died out, then those defense mechanisms would become wasteful, and organisms that didn't have those defense mechanisms would be more efficient. That would open the door to the development of new predators. The situation you're describing is not a true equilibrium, in other words.
True, but in such case, defense mechanisms don't just disappear from the gene pool, they just get deactivated. The second time they are going to be much faster to re-evolve, making the disappearance of the second appearance of predators even faster.
The predators will never disappear in the first place.
The fewer predators there are, the more wasteful defense mechanisms are, and therefore the more disfavored they are by natural selection. The more predators there are, the more defense mechanisms are favored. The equilibrium is neither zero defenses nor 100% effective defenses against predation. It's somewhere in-between.
The predators get to evolve too, by the way. There's no 100% effective defense against all forms of predation.
> If you reach a point where one organism developed enough mechanisms to resist simple predators and that their advanced predators die out, I think it would be impossible for evolution to get out of that dead end.
Evolution works on the level of individuals. Even if you end up in a situation where you have only clones of a single organism populating whole planet, these clones will compete with each other. Because of different environmental conditions, random mutations and distances this super successful organism most likely will still undergo speciation.
But what if you have already reach optimal growth and optimal energy efficiency?
If you have ever played with evolutionary algorithm, you have seen that it is very easy for a system to just "win".
Want to optimize a thing that heavily depends on a mass/surface ratio? Oh, a sphere is the perfect solution. Evolution can't beat it.
Yes, maybe there can be various colonies of photosynthetic organisms competing over millionth of percents of efficiency for billions of years. That's what I call a dead end of evolution.
You should keep in mind degrees of freedom of whatever you were playing with as well as complexity of the fitness function. Simple optimization problems have simple solutions. Physical, sustainable self replication is anything but simple. As far as I know humanity is not able to engineer anything that would be self replicating to the point where evolution could kick in. We have limited success at reverse-engineering nature but that's about it.
> Yes, maybe there can be various colonies of photosynthetic organisms competing over millionth of percents of efficiency for billions of years. That's what I call a dead end of evolution.
I would call that a plateau, because that was the state of Earth for about one or two billion years.
I think overall we agree - transition from single cell life to current level of complexity is not an easy one. We are significantly more likely to find single cell life in the universe, than anything that would resemble animals.
But you should also remember that Earth was not uniform in space and time, photosynthesis does not work equally well everywhere and overall conditions change a lot over millions of years. So even single cell life will be damn complex and dynamic on a scale of planet and evolution.
What if the substance is abundant? I suspect (here again, just an intuition) that our planet is actually exceptionally good, not for life to appear, but for evolution to occur.
One theory of abiogenesis supposes that life started in hydrothermal vents, in conditions that are very far from what is considered "habitable" for the current life (very hot water, high pressure and, IIRC hard acidity)
Maybe these are the only conditions for life to start, but does not offer a lot of room for improvement. Maybe there is just so much things you can do to efficiently colonize interstices of volcanic rocks. But then you have a whole host of conditions offered to you: a gradient of temperatures and pressures, light, storms, changing currents, varied geology. And then later on, dry lands, of a varied range of temperatures.
If the conditions for abiogenesis and evolution to occur are very different, Earth could be unique in that aspect: how many oceanic planets on a stable orbit will still have days, tides, seasons, storms AND hydrothermal vents of the correct type to generate life?
If you reach a point where one organism developed enough mechanisms to resist simple predators and that their advanced predators die out, I think it would be impossible for evolution to get out of that dead end. I am not sure that getting unstuck is a universal feature of life.
Emergence of sexual reproduction, of multi-cellular organisms, are all very weird phenomenon that I think are risky to take for granted.
I mean, it feels like playing Conway's game of life: Often, when you start a random one, it all dies out. It often gets stuck in a position where just a few things vibrates. Some last longer. Others go on forever but are rarer.
My intuition (which can be dismissed without argument) is that life is similar: if the conditions are right, it may lead to emergent evolutionary behaviors that eventually can lead to intelligent life, but that's not the most common outcome.