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Trying to consider how a walking, socially-active sapient plant would evolve and the world it would live in. More specifically, how would something which is essentially a walking tree living in a dense-atmosphere planet see the world.

Assuming the conditions were ripe for such a thing to appear, how would it see the world around it? Would it be pseudo-imperialistic, needing literal living-space? Overly pacifistic, as a creature with a pretty varied potential diet? Scientifically curious, being able to stay awake basically all the time for an entire season in what's probably a dense, complex environment and developing a society within said environment? All three?

If I were a betting man I'd say the best type of planet would be like Venus with season-long days and nights- but without the "ultra-dense acid cooker of death" element, more like a much-warmer Earth with less water. Throw in a decent moon, that seems to be the glaring thing Earth has that our rocky neighbour lacks.

Would these conditions be enough to stimulate the development of plant/animals that could become intelligent? The thick atmosphere and slow day/night cycle might be favourable for fully migratory photosynthetic life that kickstarts this process.

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    $\begingroup$ Welcome to Worldbuilding! Generally, this would be easier to read if it were split up into paragraphs. In addition, there's a lot of sub-questions in here, so you might want to think about splitting this post up into multiple posts, with one question being asked per post so that answers can be more focused on what you're looking for $\endgroup$ – Mithrandir24601 Nov 21 '17 at 23:41
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    $\begingroup$ I regret that this question is much too broad. Please revisit our guidelines to understand what makes a good question. But, basically, you're asking for too much in a single question. Asking us to develop an entire biome with variables in ecology, meterology, and planetary dynamics is well beyond what a good question can ask. There are many questions on this site about Venus. I recommend you review them to see if they answer some or all of your questions. $\endgroup$ – JBH Nov 22 '17 at 0:04
  • $\begingroup$ Hi adb1, I reformatted your paragraphs. It takes two presses on ENTER to create the necessary line spacings between paragraphs and not one. I had the same problem when I joined Worldbuilding SE, until I learned better. $\endgroup$ – a4android Nov 22 '17 at 4:15
  • $\begingroup$ Hi guys, thanks! I'll reword the question, thanks for your editing. $\endgroup$ – adb1 Nov 22 '17 at 19:09
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    $\begingroup$ You should read Forward’s Marooned on Eden for ideas on intelligent plants. This has also been discussed before here — I recall giving that same reference before. — later — yes, see worldbuilding.stackexchange.com/questions/52483/… $\endgroup$ – JDługosz Nov 23 '17 at 22:30
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First of all, plants do not live on photosynthesis; all this does is facilitate an endothermic reaction that takes CO2 and water and converts it to O2 and carbohydrates. Plants actually need O2 and sugars to create the energy of life through exothermic reactions (like all life on Earth); the difference is that they've evolved on a planet that initially had virtually zero O2 in the atmosphere so had to use the energy of the sun to generate their own.

Of course, on a toxic new earth, many of the complex minerals required to sustain life was in the mineral surface so it would make sense that they would evolve roots to keep them in a single favourable space that they could effectively 'mine' for the minerals necessary for growth et al.

The problem I have with sentient plants; photosynthesis is a very energy intensive exercise and is only likely to evolve in a world where it becomes the only source of O2 and the carbohydrates necessary to sustain life. Nervous systems also are quite energy intensive and actually use electrical 'current' to drive and power them.

IMHO, this is the primary reason why no plant has ever developed even a rudimentary nervous system; it couldn't provide any tangible benefit to a life form that's stationary and can't react to an adverse environment in any other manner than dying. Photosynthesis on the other hand does add value and if you can only put energy into one of them, the latter is the one to choose.

Intelligence takes even more energy again; a human's energy requirements break down to around a quarter of that energy feeding brain activity. This is why beanies are so effective at keeping people warm in the snow; a LOT of the heat we generate and give off is through the head.

The practical upshot of this is that a 'creature' that has developed photosynthesis AND intelligence will be massively energy intensive. That energy 'cost' would have to fall below the opportunity benefit, and on Earth at least, that would be rare.

On your Venus(ish) world however, perhaps there are conditions that could make this work. I'm thinking of a thick atmosphere that contains CO2 and a 'nutrient soup' of enzymes, proteins, water (humidity), etc. The nutrients mean that a plant could evolve to be mobile because no location is especially more beneficial, and movement has advantages in adapting to changes in environment. The photosynthesis creates just enough O2 and sugars for energy production, which gets used immediately by the plant. The remaining heat energy absorbed somehow goes directly into the plant in a manner similar to photovoltaic solar cells, effectively powering a nervous system outside the chemical processes used for metabolism. You still need a reason to invest in intelligence and social interaction. The only one that comes to mind in this environment would be sex.

Plants on Earth are effectively androgynous but imagine a scenario where your venus plants are androgynous but with a twist; they can't self-pollinate. This scenario precludes insects as a pollination method; that would be easier and therefore social interactions would not develop. In this case, we'll say that pollination can only occur through direct contact, 'flower to flower', so to speak.

These mobile plants now have a reason to seek each other out (procreation) and mate selection also becomes an issue. Ultimately, the benefits of cooperative behaviours manifest, and communication, social structure, possibly tool building all ensue.

Given the simplicity of the nervous system and intelligence likely to develop, I'm going to assume that we're not talking the development of eyes, mouths or other 'conventional' sensory organs. Let's assume that contact is purely tactile. Communication would therefore likely be tactile in nature, probably some form of chemical transference. This would initially be limited so simple instinctual and (possibly) emotional concepts, but full sentience would require either a larger range of sensory inputs, or a LOT more time. Either way, it would be VERY interesting to see this in action.

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  • $\begingroup$ I appreciate that; if it was favourable for plants here to move around in an earth-like environment we’d see that eh? $\endgroup$ – adb1 Nov 24 '17 at 10:44
  • $\begingroup$ So a nutrient soup? What about some kind of airborne plankton- would dense atmosphere enable that? I can figure Pseudomonas and other soil bacteria end up in clouds, could a eukaryote cell manage in a partly higher bar gas cloud? Maybe have small air vesicles? What’s the upper limit on air algae then... end up with flying green coral reefs? $\endgroup$ – adb1 Nov 24 '17 at 10:48
  • $\begingroup$ Yep, actually plankton would be more likely... $\endgroup$ – Tim B II Nov 24 '17 at 20:10
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Water is very scarce on such a world, so photosynthesis will be limited. The best way is to store oxygen into flotation bladders rather than releasing it into the atmosphere. This will save precious oxygen as well as provide buoyancy above the hot hellish surface.

In order for that life to evolve, some water should have been present at the early geological stage before the runaway greenhouse effect bagan. It is theorized that Venus had much more water previously. At that time the sun was not as bright as it is today and life could have started. Once life has formed, it will adapt to the gradual change to what Venus is today. It is likely that single-celled life is the first to adapt, and evolve further from that point. It may become airborne (It's easy for single-celled), and be carried to the upper atmosphere. It will adapt to the dwindling water resources by tapping the clouds of sulfuric acid and use it as solvent.

Life evolving to multi-cellular stage store the precious oxygen in specialized organs. It is lighter than CO2 and will serve as buoyant AND for breathing. Long days and nights offer new challenges. If the planet rotated fast, it's not much of a problem. If it rotates slowly, then riding the winds may prove useful. Dealing with the long nights requires storing enough oxygen as well as slowing-down metabolism. That is why photosynthesis may be essential even among non-plant creatures on the planet. This will make lighter-than-air flight (like airships) very common among animals aw well as some plants. Think of seaweeds with flotation bubbles for instance.

Thick atmosphere, strong winds and corrosive atmosphere may allow soil minerals to be carried to the higher atmosphere and feed the airborne ecosystem.

The atmosphere does not filter UV light. It may be used to perform photosynthesis as a way of tapping that resource.

DISCLAIMER: This comment does not enter into the details of why and how the conditions on the planets became Venus-like, but deals with ways of adaptation. Click here to see how Venus may have become what it is today.

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If you are talking about today's Venus, you need to invent a whole new biochemistry. You have two issues:

Thermodynamics.

For anything to happen you need a flow of energy. On earth energy comes in in the form of 6000K visible light radiation from the sun, and leaves a 300K infra-red radiation. In between, plants use this.

There are some oddball life forms that use stored chemical reactions -- tube worms around black smokers on the ocean floor. The energy source isn't plentiful.

Venus gets some light at the surface, so some form of light to chemical energy is possible.

Temperature

Venus is at a temperature of something like 860F. You aren't going to be using water as a solvent for your chemistry. You may be able to base biochemistry on silicones, but you've got some stiff homework ahead of you.

Ecology

What keeps it from covering the entire planet? Example: We aren't knee deep in wolves because there aren't enough deer and moose. And we aren't chest deep in deer because there isn't enough vegetation to feet them.

Reactions to this: Many species are territorial: They require a certain area of land to browse for food. Bears will attack other bears in their territory. The stress from this kills young bears. Wolf packs are territorial, although the territory and pack size vary a lot depending on conditions. Many birds are territorial. Much of bird song amounts to "My Tree!"

Some animals are solitary -- Cheatah's, cougars, pocket gophers. Some work in family groups -- coyotes, squirrels. Some form larger organizations -- wolf packs. Lion prides, deer herds.

So ask yourself -- what are the limits to growth? Why isn't the population bigger? Decide on these, then ask a question that is more specific.

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  • $\begingroup$ In answer to your question; I'm only considering Venus as a model in terms of its rotation speed, and maybe atmospheric density. Making that pseudo-Venus Earthlike is just less headache all round. $\endgroup$ – adb1 Nov 23 '17 at 21:42
  • $\begingroup$ I was thinking that, concurrent to the super-plants, hyper-active insect analogues develop. Since their biochemistry is more or less the same year-round they could keep up with the plant-animals and get the upper hand in night-time, so lots of "predator" herbivores that come out in the night season. $\endgroup$ – adb1 Nov 23 '17 at 21:44

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