Let's suppose that on a planet the intelligent beings started a nuclear war and destroyed most of the surface of the planet. Now, the intelligent beings are all extinct. Assuming this were an earth-like planet with life forms just like those on earth, what sort of life forms would evolve after the nuclear war? By this I mean life forms that evolve from the species that survived the nuclear war.

  • $\begingroup$ There are entire books about that. We can't write you a book here. Narrow it down to more specific conditions, time frame, species or biomes etc. $\endgroup$ – Mołot Feb 7 '18 at 16:14

Mushrooms are probably a best bet for evolving! Mushrooms are very versatile and are decomposers, meaning they thrive by breaking things down. With the death of a dominiant species, they would surely feast.

Plus, there is a special type of mushroom called radiotrophic, meaning they can convert radiation to chemical energy! This would give them a very significant advantage

Mushrooms, exposed to radiation over time, and feasting on a slew of creatures (dominant species and whatever went down with them) could surely evolve into something interesting!

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    $\begingroup$ Evolution takes several generations to work. Decomposing corpses last way less then several generations. At a certain point your mushrooms will starve. $\endgroup$ – L.Dutch - Reinstate Monica Feb 7 '18 at 6:16
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    $\begingroup$ Even if Dutch wasn't correct about food supply (and he is), continuous food supply can be detrimental to evolution. Look at sharks; they've remained the same for nearly 200 million years because they're perfectly adapted to their job of cleaning up the oceans of sick or dying animals. Environmental change is what really forces evolution into high gear. That said; sentient mushrooms would be an interesting wrinkle, especially if it evolved from that zombie fungus that infects ants. $\endgroup$ – Tim B II Feb 7 '18 at 6:33
  • $\begingroup$ Radiation kills decomposers. In Chernobyl, all the trees are dead, but perfectly preserved because no bacteria, insects, or fungi could make them decompose. Mushrooms, however, are the best bet for a prime decomposer because of their resistance to radioactivity and even ability to feed on it since insects and bacteria really can’t. The corpses wouldn’t be decomposing unless the mushrooms were absorbing them $\endgroup$ – user47524 Feb 7 '18 at 6:34
  • $\begingroup$ Hi Kess. That might be so, but surely even a perfectly preserved biomass would run out in time because it's not being replaced. I'd be interested in seeing numbers on how many mushroom generations could survive on a preserved biome of a given size. Perhaps that's a good question for the site... $\endgroup$ – Tim B II Feb 7 '18 at 6:38
  • $\begingroup$ Mushrooms have short generations. It may well take several generations to cover a corpse. And something interesting might happen when the mushrooms start running low on food. The mushrooms that survive running out of corpses are going to be the ones showing interesting evolutionary effects. $\endgroup$ – Brythan Feb 7 '18 at 7:13

The correct answer to this question really depends on just how badly the surface of the planet was destroyed. Life is more tenacious than we generally think and if the nuclear war merely took out the cities and left most of the regional areas alone, life could survive quite well.

While not exactly a nuclear blast, Chernobyl was (at the time) seen as a massive disaster and the meltdown caused massive contamination, yet plants have thrived in the area. This has left many scientists scratching their heads, but it would appear that if the contamination in certain areas of the planet are only contaminated up to a certain threshold (we don't currently know what that threshold is) then at least some plant life is going to survive, possibly thrive.

This is very important. You can't have animal life without plant life, at least not for very long (geologically speaking).

Animals though; that's something else. Most animals are not going to cope with radiation. The mutations alone will cause all sorts of problems and many animal species can expect to go extinct, or have substantially reduced population sizes.

The exception to this rule is the cockroach. They won't survive nuclear blasts of course (the linked article explains that) but those in the regional areas should survive the subsequent radiation quite well. Many invertebrates may well fit into this category but I don't have specifics to hand.

But, let's assume for a moment that the main species that survives the holocausts is a cockroach. That means that in future eons, it's possible that the next advanced species to exist would be some form of insect.

I say possible, but it's still unlikely. Insects don't have lungs so they have a limit to their maximum size because they have to absorb O2 through the surface of their bodies, and that O2 has to reach the inner most areas of their bodies. This limit on size and O2 absorption methods also puts a limit on their brain size, meaning that human like intelligence in atmospheric proportions similar to those on Earth today is a practical impossibility for cockroaches.

The one caveat on all this is a nuclear winter. The answer above assumes that enough of the earth's surface gets at least some sunlight to support plant growth, allowing some plants to survive. If enough bombs drop and throw enough material into the sky to block it out for a year or more as many suggest would happen in a nuclear war, then all bets are off for complex life.

We'd be starting again from whatever bacterial lifeforms manage to hang on.

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  • $\begingroup$ "limit on their brain size" - how about skin / exoskeleton filled with neurons in place of a traditional brain? $\endgroup$ – John Dvorak Feb 7 '18 at 6:17
  • $\begingroup$ Interesting Idea, John. Distributed neural processing; only problem might be you lose a leg to a predator and forget your father's first name. :) $\endgroup$ – Tim B II Feb 7 '18 at 6:28
  • $\begingroup$ The distributed processing idea was developed in novel Blindsight. $\endgroup$ – Ville Niemi Feb 7 '18 at 10:01
  • $\begingroup$ Just a nit to pick: It would take more than 1 year without light to set the world down to bacteria being predominant. There are the sub-marine and cave life-forms which can survive with less light or no light, but even for normal surface life there is hope. Some trees adapted to winter dormancy might just stay dormant longer. And to start anew, many seeds will still be viable and start to grow at that time. This could be the case possibly even without 2 or 3 years of light, let alone 1 year - I'm not sure what the limit would be. $\endgroup$ – Loduwijk Feb 8 '18 at 19:10

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