Today, a Sea Slug. Tomorrow, ... ?

Severian's friend the Green Man always seemed quite plausible to me. I hadn't realized just how plausible. Apparently a sea slug has incorporate algae genes into its genome and produces and uses chlorophyll inside its body: http://www.sciencenews.org/view/generic/id/53496/title/Sea_slug_steals_genes_for_greens,_makes_chlorophyll_like_a_plan

There's still a question of him being able to intercept enough sunlight to be more active than a slug. A man-sized silhouette in Earthly conditions intercepts less than 100 calories worth of sunlight a day. From the Green Man's sunny smile, his people apparently still have humanlike teeth, so presumably they can eat a variety of food to make up the deficit, but I'm not sure if reducing your food needs by 1/30 is worth the hassle. It might be that the chlorophyll isn't strictly for food, but for sensory purposes; can anyone think of an occasion when the Green Man would need to be able to feel a shadow falling on him, or would have to distinguish between bright lights of different character?

That's pretty amazing, if it's confirmed.

Is that with perfect efficiency? Gosh, are you seriously telling me to do the calculation? Half a square meter in sunbathing position, 1 kilowatt, 8 hours, that's 14,400 kJ or about 3400 big calories. You're assuming something like present photosynthetic efficiency.

The sun could be brighter in his time than ours, and genetic engineering could have improved the efficiency of photosynthesis and that of metabolism.

I can't We do fine with vision. Though human color vision is rather klugy, I gather, and those same genetic engineers could probably improve it without any cost by making it more like birds'. Jerry Friedman

Did you see the thing last year? A predator microbe that becomes photosynthetic if it eats this other microbe, then fissions into the original separate microbes again?

He said it was pond scum, so I presume it was something vaguely like pond scum.

maybe, but 30x as efficient?

Missed that one.

Sure. I just wanted to know what you were presuming.

As you said, he probably still needs to eat. If between more sunlight and more efficient photosynthesis and metabolism he gets ten times as much as we would, it would reduce his need for food by about 1/3, which seems worth some hassle. Jerry Friedman

Furthermore, if those calculations are based on American calorie intake, you could cut the Green Man's food energy needs by up to 50% just by changing that assumption to a level more typical of the rest of humanity.