Could human skin be photosynthetic?

Thanks. That's interesting!

Pete

Could work. Approximating a (naked) body has a 6' by 2' area (about 1 sq. meter), assuming the body is lying in direct sunlight, and assuming sunlight has an intensity of 1 kW/sq.meter, you get about a kW of available energy. And you only need, what, 100W of energy to maintain bodily functions (at rest). Maybe more, to avoid predators or psychotic engineers...

Of course, photosynthetic organisms aren't 100% efficient. Herbivores eat quite a few plants each day, and you know how long it takes for a plant to reach maturity.

Don't forget compounds which can take gamma radiation and downconvert that to visible wavelength electromagnetic radiation.

We just had our HAZWOPER refresher today at work. The innards of the Ludlum were discussed, where sodium iodide emits visible light when struck by gamma photons. I didn't know that...!

Michael

Interesting.

Radiation doesn't have to be ionizing in order to be photosynthetic.

If one allows a flight of fancy - we can imagine a nano-engineered self-replicating machine system that are deployed throughout Earth as a spore like device and when it touches human skin it invades the skin and inhabits it much like a fungus,The machines operate on sunlight. The fungus like machines ideally would invade the blood supply and circulate the blood through them, providing nutritional molecules made from the environment and processed by sunlight energy.

The sun produces 1,000 watts per sq meter,

According to medical models of metabolic rates;

A human body uses 32 kilocalories per hour per square meter. Projected area in sunlight (the area of your shadow) varies- but may be 1/3 this amount. And sunlight is available about 1/6th the time - depending on weather.

So, you'd need 18 times this amount - 576 kilocalories per hour per square meter- NET production. 2,411 kilojoules per square meter per hour. that's 670 watts per square meter.

The sun produces 1,000 watts per square meter surface normal to the sun's rays. So, this nanomachine fungal infection would need to be

The devices should also inject neurochemicals into the blood, psychoactives, that cause people to feel satisfied and happy to be in sunlight for long periods of time with no clothes on.

Another possibility to reduce time in sunlight is to implant wings on to the 2 through the 6th thoracic vertebrae, and have them controlled with peripheral nerves connected to the brain for that purpose. These black leathery 'wings' could easily double the surface area naturally found in the body and easily be presented to the sun quite naturally independently of body orientation.

Person's so infected would not need to wear clothes, and so this infection would cause them to want to shed all their clothing.

Their skin would take on a dark reddish hue - ranging from jet black to deep red and be leather tough.

As mentioned they need not eat or drink under normal conditions. The machine systems would also be capable of providing a wide variety of neuro chemicals - as well as communicate with some sort of variant of blue-tooth technology with other swarms nearby. This would implement a sort of mental telepathy between infected cohorts.

A film forming over the eye of flourescent nanomachines could also produce visual hallucinations on demand - and machines could stimulate thenatural skin in controlled ways. Sounds would also be produced by nanomachines invading and stimulating individual hairs in the cochlea. In this way virtual reality could be implemented.

In the book AMERICAN VESUVIUS there is a chapter on how low velocity particle clouds of great mass can lift and transport individuals and objects great distances without destroying them. That is, the thrust imparted by a jet of material is;

F = mdot * v

Where F = force newtons mdot = kg/sec v = velocity

Small independently flying objects at moderate speeds of 10 m/sec (36 kph) massing as little as 10 kg (22 lbs) can be coordinated to lift a person on demand.

The nanomachines infecting the skin and organs of an individual could interact with free flying nanomachines to cause individuals to be lifted up and transported great distances at high speeds in short periods of time.

These clouds could be solar powered. They would be inky black clouds that absorb the sunlight and use that energy to jet around - coordinated to produce propulsive effects. Objects could be carried around, including people.

The air naturally wouldn't have sufficient materials to supply all the food products needed by an individual. Some devices would feed on the soil and when persons passed, they would crawl up the passing persons body and be absorbed by the skin. Other material would drop off in a cloud as it was needed by the stationary population. This could all operate seamlessly.

So, there would be stinking yellow/brown clouds swirling angrily around the feet of individuals as they walked through this wasteland, their skin would be black to black red, with small leathery wings, yellow bloodshot eyes, distended ears and gut, useless anus and urinal tracts, inky black clouds swirling overhead in their minds filled with impulses to sit still in sunlight, and voices of a billion others all talking at once...

Nice place to visit, but I wouldn't want to live there.

Make that bacteria, and you've got the probable scenario of how plants acquired chloroplasts a billion or so years ago. But if people ever do get to photosynthesise, think of the implications for future evolution...

Surface area. The bigger, the more food you'd get, and the better you'd thrive. One available source of extra area is the otherwise rather useless ear. We'd all end up looking like Prince Charles.

Sunlight and water. UK's no good, Nevada neither. All move to somewhere sunny and swampy- Florida?

Competition for sunlight- taller is better to gather light (overshadow the competition), but for the same resources short is better for using resources for muscle, to shove the tall weedy ones out of the way. So there would be competition between the tall, beanpole build and the short muscular build. Or perhaps the short muscular ones would rely less on primary production, but eat the tall thin ones.

I would say you stole my fancy! :-) There are a few catches though.

1. Photosynthesis yields starch. Animals need glycogen. Starch breaks down only in digestive system!
2. How would the body carry the synthesized material to lever from skin?
3. Saline glucose injection causes human beings to form and release a lot of gas. I'd say the idea 'stinks'.

Another set of very interesting possibilities:

1. Suddenly war would shift from Iraq to Bangladesh (for America would need sunlight and water more than petroleum)
2. Industries like textiles, garments and agriculture have a sudden stop (or at least significant slow down) and many others follow (like fertilizers, dyes, fashion etc.)
3. Body appearance related industry, tourism, "near solar system" travels, entertainment industry, recreational drugs and similar industries thrive
4. Deforestation accelerates, obesity jumps (and so does health care industry)
5. >90% of population of the world works to secure food. In a long run, human photosynthesis would just break down civilization, in which, society does not yield food unless human beings do something useful

Ah an experiment worthy of an Ig Nobel prize perhaps :-)

Perhaps space travellers should get a good tan before thet set off for mars?

You've been reading too much Michael Crichton ;)

Tim

-- Deep Fryer: A very philosophical monk. Website @

Wow! Entertaining speculation. Thanks.

It aligns with a speculation of mine. Why did plants never evolve the ability to move around? Surely the ability to go from a water hole to a well lit place would be a decided evolutionary advantage. Is perambulation a pre-requisite for higher intelligence? Plants have been short changed generally regarding a number of features--sight, hearing, locomotion, intelligence, ...(others?) Well at least plants have sex and photosynthesis.

Perhaps relevant: The juvenile sea squirt wanders through the sea searching for a suitable rock or hunk of coral to cling to and make its home for life. For this task, it has a rudimentary nervous system. When it finds its spot and takes root, it doesn't need its brain anymore so it eats it! (It's rather like getting tenure.) From CONSCIOUSNESS EXPLAINED, by Daniel Dennett, p. 177

John

They do move. Ever turned a potted plant around? Its leaves will eventually turn so that they are again facing the sun.

My speculation is that it 1) takes too much energy to move around (unless it's limited to... eh, one inch per day), and 2) uprooting and digging a new hole by itself is just too hard.

Michael

A. An area like a human body wouldn't produce enough photosynthetic "stuff" to live on. B. Everybody would have to run around naked, and let's face it - with about 95% of the population, you wouldn't want to see them naked. ;-)

Cheers! Rich

Though to be honest, those 95% of the population would get great photosynthesis per capita.

Tim

-- Deep Fryer: A very philos>

;-)

But if it only provided a small bit of energy, it still would be reinforced by evolution. For example, if in two competing bacterial species one species outgrows the other by a small percentage, soon only one species will exist. If two human tribes face hard times, something like skin- photosynthesis might let one tribe pull through where they otherwise would die.

((((((((((((((((((((((( ( ( (o) ) ) ))))))))))))))))))))))) William J. Beaty Research Engineer beaty a chem washington edu UW Chem Dept, Bagley Hall RM74 billb a eskimo com Box 351700, Seattle, WA 98195-1700 ph425-222-5066

Heh.

ANYWAY... people here seem to be assuming that for human photosynthesis to evolve, it would have to supply 100% of body energy input. Why? What if it only supplies 1%? In conditions where death by starvation was a constant danger, any creature which developed even a poor version of photosynthesis, might survive to outbreed all competitors.

I could even reason thus: if human photosynthesis was possible, then we'd probably have evolved that trait already.

The only difficulty has been in assuming that if photosynthesis was happening, human skin would have to be colored green. The article about the Chernobyl fungus suggests that brown skin might be a signature of photosynthesis capability... but based on ionizing radiation rather than visible light.

On the other hand, mammailia rather than humans would have evolved the trait, and we'd expect to see tropical animals having bare skin. HEYYYY! Is animal fur typically opaque to ultraviolet? (Do people get scalp- sunburn despite thick hair?) Maybe they wouldn't need bare skin.

((((((((((((((((((((((( ( ( (o) ) ) ))))))))))))))))))))))) William J. Beaty Research Engineer beaty a chem washington edu UW Chem Dept, Bagley Hall RM74 billb a eskimo com Box 351700, Seattle, WA 98195-1700 ph425-222-5066

You'd most likely have deep tissue damage, and maybe cancer. Gammas penetrate.

It's no more effective a gamma shield than any other light molecule, that is to say, not very. It's still made of carbon, hydrogen, and nitrogen, and the molecular structure doesn't influence gamma interaction.

Just because a substance converts radiation-strewn ions into some non-thermal form of energy (like, say, a phosphor converts it to light) that doesn't mean it's any better an absorber.

"Due to their high energy content, they are able to cause serious damage when absorbed by living cells."

"Shielding for gamma rays requires large amounts of mass. The material used for shielding takes into account that gamma rays are better absorbed by materials with high atomic number and high density."

John

The way a critter gets enough energy to move around is by eating plants. It gets to eat plants by moving around.

Photosynthesis is not very efficient, 0.1 to 1% overall usually. I suspect what limits it is CO2 availability, which shortage we are working on.

John

Actually as I understand it, nitrogen is a bigger limiter. Plants cannot use what's in the air and so rely on nitrogen fixing bacteria. One of the biggest roles of crop rotation is to plant a crop that supports nitrogen fixing bacteria to enrich the soil for subsequent crops.

There is a limit to how much nitrogen a plant can absorb, I suspect the same is true of CO2 although I don't know where the limit is.

Anyone have any information on what CO2 variation does when the nitrogen levels are not raised?

Robert

Too interesting of a story.

And too little doubt that the "destruction" of skin & organ cancer through radiation is improper, instead focusing the radiation and combining with this recent discovery should promote good cell growth.

Perhaps but more complex is possible advancement in stem cell growth as well.

While reading this, I can see through the window our purple leafed Norway Maple. There is also a purple leafed plum.

John