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Picture this, humans (or human-like sentient beings) having the innate ability to photosynthesise their food in a similar manner to plants - thus providing all the nutrients required for sustained life.

Let's also assume that the humans have evolved to have the same brain capacity as we did when agriculture started.

Surely, such a difference would result in the human race not needing to go through the 'agricultural revolution' of our early history, thus potentially freeing up time for other pursuits - would there be an impetus for technological development if agriculture was unnecessary?

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  • $\begingroup$ Just food for thought and inspiration: in the Starcraft lore, the Protoss have been photosynthetic ever since their beginings. And they are more technologically advanced than Terrans (humans) $\endgroup$ – Renan Jul 22 '16 at 3:15
  • $\begingroup$ Related: worldbuilding.stackexchange.com/questions/41318/… $\endgroup$ – James Jul 22 '16 at 13:43
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    $\begingroup$ You'd need agriculture just to sustain humans. Because photosynthesis requires more than the sun. You may be talking about a different magical process--I'd say don't call it photosynthesis, just say we get everything we need from the sun. I do have some issues with this evolutionarily--how do our brains develop if we have no need for tools? Pretty much, some harsh thing has to push evolution--before you even get to tech, our brains developed as a result of hunting and gathering. It's not just tools. would there be impetus for brain development if the need for food were taken out. $\endgroup$ – Erin Thursby Jul 22 '16 at 16:36
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    $\begingroup$ A long time ago, I read a short article about world design. It briefly talked about photosynthetic animal life and how they might develop intelligence and mobility. The example presented was an amphibious creature that for most of the year floated in the water with a large frill spread out to increase surface area. However, during the fall fruits and nuts ripened giving incentive for these creatures to bunch up their frills, and seriously compete among themselves in finding and consuming this nutritious and high-energy food and move into seriously competing among themselves for mates. $\endgroup$ – Michael Richardson Jul 22 '16 at 20:53
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    $\begingroup$ You may want to read this xkcd 'What If?' article, in a nutshell, a human sized creature doesn't have enough surface area to collect enough solar energy to sustain itself (think about how much area the grass that a single cow eats in a day covers, compared to the area of the cow's body...). Obviously, you can always ignore that bit if it gets in the way of your story... $\endgroup$ – G0BLiN Aug 25 '17 at 14:40

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Absolutely! Besides agriculture, humans would still benefit from technology for:

  • Improved defense against predators.
  • Improved weaponry for defending territory from rivals.
  • Improved medicine.
  • Improved shelter from the elements.
  • Improved nutrition--just because they photosynthesize doesn't remove the needs for vitamins, minerals, or most importantly, water.
  • Satisfaction of curiosity (which seems to be a very innate part of our species).

This is assuming that your humans are fairly similar to us except that they can generate glucose from sunlight (which probably isn't possible, but you didn't tag this with 'science-based' so I'll let that slip). In reality if a race of photosynthetic humanoids were to exist, it would likely be so different from us that their physiological and societal needs might differ greatly for our own (thus potentially invalidating large parts of my answer). Might make for a good question!

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  • $\begingroup$ Note that a human sized-organism with human brain capacity would probably not be able to fill all their dietary needs using photosynthesis alone (see this question and the xkcd-what if linked in a comment above). But without a science-based tag this probably doesnt matter that much. $\endgroup$ – Nicolai Aug 27 '17 at 10:56
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So the premise of your question is flawed in a couple ways...

Picture this, humans (or human-like sentient beings) having the innate ability to photosynthesize their food in a similar manner to plants - thus providing all the nutrients required for sustained life.

So...plants don't magically make nutrients right. They absorb nutrients and water from the ground to make food. Your photosynthetic humans would still have to ingest nutrients to fuel photosynthesis.

Also keep in mind that while an amazing feat and the basis for all more advanced life... photosynthesis is very very in-efficient.

Let's also assume that the humans have evolved to have the same brain capacity as we did when agriculture started.

Roger.

Surely, such a difference would result in the human race not needing to go through the 'agricultural revolution' of our early history, thus potentially freeing up time for other pursuits - would there be an impetus for technological development if agriculture was unnecessary?

At a cursory glance you might think so but agriculture is still the most efficient way to get food to large groups of people. Its takes something like 1.2 acres of arable land to feed a single human for a year...that's how inefficient photosynthesis is...

As I mentioned in this answer while it could hypothetically help a humanoid, photosynthesis would be a vestige that is not longer particularly useful or necessary. We burn so much more energy simply existing (respiring, digesting, staying warm, etc) than a man size plant can produce that its just not a feasible system. In the end, even if we could, technology (farming included) would still be necessary.


Now if you're not to worried about the science you could come up with some alternate form of photosynthesis that is more efficient...I as a reader would accept the premise even if I know the science doesn't really support it.

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The amount of energy provided by photosynthesis over the surface area of the human body is nowhere near enough to provide for any active "animal" lifestyle. Even if they became completely sedentary, sitting out in the sun all day, the amount of energy used by just thinking would at least make a serious dent in the energy produced, probably using more than would be produced.

So agriculture is still a better way to gather energy from the sun, even if not as directly efficient.

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Agriculture is absolutely required

Photosynthesis doesn't nourish a plant. In fact, photosynthesis requires carbon dioxide, water, and sunlight to produce sugar (glucose) and oxygen. So, what changes in society? Not much.

(a) The sugar industry (and along with it the confection and soft drink industries) is non-existent.

(b) There's a bit less global warming.

(c) Humans would be capable of somewhat larger bursts of speed/strength due to the higher availability of glucose.

(d) Our buildings would be built to permit light much more than they are now. Basements would be all but nonexistent.

(e) I suspect there would be much less variance in skin color.

(f) Locking a child in a room would move from a class A misdemeanor to a class B felony.

That's about it. As for the impetus for technological development, you seem to be forgetting the entire industrial revolution, of which the agricultural revolution was only a part.

The closest comparision I can think of off hand is the development of northern snow-laden people vs. the equatorial people who live in warmer climates. The short growing season and long period to think during the winter breeds new ideas. Since photosynthesis doesn't relieve us of the need to eat, the impetus is still alive and strong.

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It is not by chance plants are sessile (an erudite way of saying they don't move much) and have a very large "skin" surface.

Photosynthesis is quite inefficient, but even if it was not, you would be hard pressed to live an active life with direct solar power. By comparison note highly engineered solar cars have average speed around 40Km/h and limiting factor is energy, because they can easily go over speed limits for short distances.

The best you could have is something with the (mean) activity level of a sloth. You could think about beings basking in the sunshine for hours at a time and then start some activity till energy lasts. A bit like cats would like to do.

Surely such a life style would encourage meditation.

Main problem, here, is why they should move at all. If they do not need to move to find their food why should they develop all complex (and expensive) machinery to move and manipulate environment?

You can relay on regression (photosynthesis is acquire is after motion), symbiosis (beings have some form of grass on their skin, instead of fur) or direct need (semi-desert climate where some rivers exist, but often change their course and "plants" need to follow or they will die).

In any case you may want to rely on some more efficient photosynthesis agent than chlorophyll to boost your energy levels.

You don't say what other fauna is present in your world. If there are other, potentially dangerous, animals then the push to protect themselves would drive knowledge accumulation.

The first to invent solar lamps would become very rich.

In general, as said, these beings are not going to be overly active, so they would probably be a race of philosophers, with some practical fallout.

Their houses would probably resemble greenhouses and they would be masters in building banks and dams to constrain the squishy rivers (if you chose the third alternative).

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Redundancy!

Since your folks are human-like, and that's a pretty broad term, your world can have these sentient beings shaped like humans but with totally different internal biology, or they can have the same goals and motivations as humans, but look completely different, shape and all. So if your human-like means bipedal, brain-heavy operating system with similar lifespans, etc, then even though they have souped up photosynthesis that produces every nutrient they need, perhaps it isn't always enough energy for everything they want to do, especially for pursuing learning in their freed up time.

Therefore, they search out redundant energy production methods to enhance or perhaps turn on additional body functions that lie dormant when not enough power available. Plus, the many technology revolutions of other kinds as mentioned by ApproachingDarknessFish would still occur.

Even more likely is still having an agricultural revolution although a slightly different looking one than ours. After all, if they are photosynthesizing beings, perhaps they experimented in grafting to themselves and bioengineering their own germinating cells to improve their own internal energy production rather than improving other plant species production capabilities for consumption purposes.

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This is a rephrasing of Could inequality and class warfare still exist in a post-scarcity society?

And I give it the same answer: the prettiest boy/girl in the room/village is always in short supply, so, even they could all just sit in the sun all day, your planty folks will be striving to impress each other, and technology will happen.

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Theoretically if they had no survival needs and lacked intellectual curiosity they might not develop any form of technology. However as has been pointed out, these aliens would require more to survive than just the ability to photosynthesize. There is also a nutrient requirement, most plants get their nutrients through their roots. However I am assuming these aliens are not rooted into the ground, so instead they would most likely have to eat animals or other plants. The only way around this I can see is if the atmosphere was nutrient dense enough to allow them to filter feed.

Filter feeding could actually provide a reason for a plant to develop mobility as it would allow them to move to better feeding grounds, however it would still likely encourage the development of technology, as starvation could still be a factor.

There are also predators to consider, as well as the natural events like severe rainstorms that would likely cause them to require shelter. The breeding incentive was also brought up, but if they are plants they would likely breed by pollination, so that might not be a factor.

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I read and upvoted other answers, so this is piling on in my own words.

Photosynthesis is only a means of providing energy to convert physical elements and chemical compounds into other physical forms useful for the plant. Put a living plant into an all nitrogen environment, at the same air pressure and with all the sunlight it normally needs, with its roots in some non-nutritive equivalent of soil (e.g. all silica sand), and it will die. It may still try to photosynthesize, but that energy has nothing to break down. Water, CO2, and other nutrients absorbed from the soil are critical to its survival.

Secondly; the first "technology" of the predecessors of homo sapiens was most likely not about food at all. To my knowledge the earliest known use of tools, before any use of shaped rocks, is the evidence that rocks were used as weapons to crush the skulls of same-species individuals: Presumably rivals. We have the fossilized skulls to prove this, from an era in which we have no shaped rocks, and the timeline indicates the earliest of these fossils coincided with about a 50,000 year span of rapidly increasing skull thickness among our predecessors.

Even given the presumption that hunting and farming are not necessary for food in any way, there are many other reasons to settle in a specific area; for example to build an infrastructure that protects one from predators, guarantees easy access to clean water, provides plenty of sunlight and has natural defenses against our own kind (other tribes) that might want to steal it. Also preferably large enough to expand the population.

Every living thing has some form of paradise that makes life easy. In fact, the main reason we did not settle in the first place was a food driven reason (we were hunting and gathering food to support ourselves and our offspring). Chances are photo-humans would settle far more quickly, with no particular reason to walk 20 miles a day, and plenty of reason to just stop and set up permanent residence in the first near-perfect place they found. (or turn it into a near-perfect place by landscape modification; diverting water, clearing away brush, forests and other competitors for sunlight, etc).

Technology and Arts could develop for some of the same logistic reasons it did in humans: Once the food supply is secure (for us by herding and farming, likely in that order), people have idle time to pursue other interests, and some of those other interests will be understanding how things work and exploiting that to make life even easier. Or safer, or more fun, or more satisfying.

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There's a lot of room for fun here. First, do note that the amount of photosynthetic leaves/hair/whatever on a humanoid form is not likely to supply enough oxygen or sugar to truly maintain an active mammal metabolism. That said...

  • Maybe your creatures have a mostly "planty" lifestyle, but are capable of animal-style bursts of activity

  • Maybe your creatures use their photosynthesis to stave off starvation during bad times, and can survive in a near-torpor just on sunlight/water/dirt. (Heck, if they're cold-blooded their metabolic needs are much less to begin with) Or they use sun power to build up a reserve to be expended in a crisis or a fight

To the actual question...

  • Since they can't just survive on light, they'll need something else; hunting, herding, planting. This opens up a whole slew of needs for technological development.

  • Even standard plants are ferocious competitors, albeit in slow motion. Your people might strain to clear land, or to build their houses higher than neighbors (to get less shade). I can see plenty of room for competition here, which means advances.

  • Food is not the only limited resource. Water, good light, green women, heck, sunnier latitudes are all worth fighting over. These guys might vie for control of nitrogen-fixing plants, or pastures containing them. Or nitrate-expelling animals.

To make things more different from standard animals ... why not make them mostly planty, but have a limited ability to process foods and move quickly in short bursts. Their conflicts will consist of lots of slow clever maneuvering for advantageous position (physical or social), then one apocalyptic burst of action.

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