Photosynthetic people
Tuesday, 12 August, 2008I was reading a recent article – “Changing the nature of human beings” – by Julian Savulescu in the Sydney Morning Herald, and he mentions this:
So one day we could have people with sonar like bats, or people with the ability to create their own energy by photo-synthesising sunlight like plants.
At first I was dismissive of the idea of solar-powered people, but then I remembered reading in a marine biology pamphlet that certain sea slugs are ‘solar-powered‘. I investigated that some more, and it does turn out that certain molluscs have a symbiotic relationship with chloroplasts that they steal from the algae they eat, which – like plants- are organisms that normally utilise chlorplasts. (Rumpho et al, 2000). One molluscan slug species, Elysia chlorotica, can survive for up to nine months without eating: just on light and carbon dioxide (Green et al, 2000), and even then the slugs die of old age not hunger. Still, the chloroplasts die after about six to ten months, and need to be replenished by eating more algae.
Chloroplasts are solar-power plants of the plant cell, just like mitochondria that animals and fungi rely on (plants have mitochondria too though). Just as mitochondria were once proteobacteria, plastids (of which chloroplasts are the most noteworthy) were once cyanobacteria, and both still have their own DNA and a very bacteria-like membrane. They have evolved to get very comfortable with the relationship, offloading much of their essential genes to the host nucleus, and now they can’t live without their hosts (then again, we can’t live without our endosymbionts).
This means, however, that if we humans wanted chloroplasts for ourselves, or our livestock or pets, we would need to genetically modify the host animal to express proteins required for chloroplast function. It has been estimated that about 70-90% of the genes required for chloroplast function are provided by the plant’s genome (Martin et al, 1998). In the case of the sea slugs, some of these genes appear to exist in the animal’s genome, although probably not enough for the chloroplasts to be able to reproduce. Which is why the slugs use kleptoplasty - removing the chloroplasts from their food.
It would probably be most feasible for chloroplasts, along with the required genes, to be added to skin stem cells and applied as a skin graft, as there is a lot of research in this area for burns victims. This approach has been used to produce proteins in mice (Larcher et al, 2001), and so should be feasible for producing sugar by photosynthesis in humans. At first this graft may require regular replacement, but eventually the chloroplasts will be sustainable within the skin.
There are a few problems.
First, the immune system may attack the chloroplasts, but maybe they will be safe from antibodies if they are inside the cell (the immune system will attack mitochondria, but only if they are present in the blood).
Second, the photosynthesising skin would necessarily be green as that is the colour of chlorophyll. I suppose the melanocytes of human skin could be engineered to produce another pigment, causing the skin to take on a different colour, but then again it might not be such a big problem to be green skinned…unless you are sensitive to Bruce Banner jokes.
Third, people may get sunburn and skin cancer when they are out ‘feeding’ on sunlight, as while the red and blue parts of light will be used, the ultraviolet component of sunlight causes damage to living cells. To absorb this before it causes damage, vertebrates have melanins (and humans augment this with sunscreen), and plants/algae (which don’t use UV light) produce screening compounds. It is likely that a derivable sunscreen pigment, which does not darken the skin like melanin, could be produced by melanocytes and absorb the UV-B light. But the idea of endogenous sunscreen is beside the point of this post (to be dealt with another time).
Last, the reaction of photosynthesis can be simplified as the following:
6 CO2(g) + 12 H2O(l) + light → C6H12O6(aq) + 6 O2(g) + 6 H2O(l)
It is now obvious why plants need to be watered – there is a net loss of six water molecules for every glucose molecule produced. This would mean that the plant-person (or algae-person) would also need a lot more water than a normal human, which would be a disadvantage in a desert environment.
Anyway, the impacts of solar-powered humans would be far-reaching. First, photosynthetic people would need less food, which would reduce the need for farmland, and would be using carbon dioxide to do this, thus decreasing the amount of this greenhouse gas in the atmosphere. This would be a major boon, especially as people start to live longer and farmland is used up by food production. In addition, as I alluded to earlier, this could be done to livestock too, reducing the amount of land required to feed cattle or horses (hairy animals like sheep or sensitive-skinned animals like pigs may be more difficult). So as humans strive for immortality, this could be part of the solution to any problems that arise from that.
So, solar-powered photosynthesising people are possible, and should alleviate food requirements…until the sun burns out or is clouded out by pollution or something.
Image credit:
The image, of the sea slug, is of the sacoglossan slug Elysia ornata. It was taken by Flickr user budak, and released under Creative Commons BY-NC-SA license.
I love the internet. It never fails to assure me that I am NOT crazy when I think of these things. I wish very much that this could happen. Some people think modifying humans is ridiculous and should be immediately stomped on, but let’s look around us…
Change and destruction is consuming us. We need to take control and use the knowledge that we have confidence in. Restoring wild land, putting an end to world hunger, sucking up excess carbon dioxide, and sporting green skin? Photosynthetic people will be the Martians who have ascended to save the planet. Hell, I’d be the first in line.
[...] to digest your pacemaker or cyborg implants (at least, not usually). It may even be possible to add organelles responsible for photosynthetic anabolism, allowing for sunlight, carbon dioxide and water to be used as raw materials for the human [...]
I’ve been searching for something like this for a while and I’ve finally found it. Very fascinating indeed.
It would seem to me that photosynthesis humans already exist, they are the dark pigmented persons of our human species, persons whose skin color is brown to black in color. Their their greater abundance of melanocyte cells than are present in the skin of Europeans produces the skin color due to absorption of the Sun’s light as plants do, but their light absorption is evidenced by brown to black color instead of green. Humans evidencing this stronger pigmentation require oxygen and ingestion of animal proteins and all the other foods in order to live just as do White persons, but their bodies also perform photosynthesis as an additional source of energy.
Perhaps, this is another reason that Africans in Africa, although living greatly in starvation continue to survive and even why the African slaves in this country who were fed on trash food like hogs, hence malnourished and worked like mules under extreme inhuman conditions including the burning Sun of the the South still very well survived; these same conditions of slavery when initially tried on the native American Indian were unsuccessful, it killed the Indians.
Scientists say Black/Brown humans also have a Pineal gland in their brain that aids in this photosynthesis process along with their melanocyte cells and also helps them produce at night the age retardant melatonin nutrient that is so extremely helpful to body repair and rejuvenation. In the European scientist research has discovered this gland has mostly calcified and thus does not operate. And this calcification occurred during evolution thousands of years ago when the Black African traveled out of Africa by the natural land bridges then in existence, to the European contient and caught in their more prolonged Ice Age the system of photsynthesis ended along with calcification of the Pineal gland and this is why the European lacks skin color.
I would love anyone else comments on my thoughts.
Hmm, it’s an interesting hypothesis, but I don’t think it fits with what we know.
First, melanocytes do absorb light with the pigment molecule melanin, but that energy is released as heat (chemical vibrations) rather than being harnessed in a chemical reaction as it would photosynthetic organisms.
The only use for light energy in humans is the synthesis of vitamin D3, which is a chemical reaction requiring UV light for a critical step. But this does not occur in melanocytes and in fact the dark melanocytes block the light required for this reaction. So the reason some humans evolved to have pale skin as they moved to less sunny regions was to maximise this photosynthesis, preventing vitamin D deficiencies.
As there is no evidence for the photosynthesis of glucose (or other metabolically important molecules) in humans, if such a process does exist it can’t be very significant, so I don’t think this can be the reason.
No, aside from having similar names there is not any real relationship between melanin and melatonin. Melanin and melanocytes are controlled by the pituitary gland (not the pineal gland), and by melanocyte-stimulating hormone (not melatonin). And there is no correlation between melatonin and skin pigmentation.
I’d heard/read that calcification of the pineal happens in Western societies, but I was fairly sure it wasn’t directly related to race but rather dietary intake of minerals (e.g. fluoride). Race and calcification may be correlated, but this could be due to dietary differences between races.
In addition, I was not aware that calcification caused the gland to not operate. Do you have a source for this?
It has been shown that some people who follow a type of Budhist meditation practice can survive for months to years without food and water. Though supernatural theories and attributes have been ascribed to this capability – the bottom line is that they are able to continue living without any food or water. No biochemichal abnormalities were found in those who let themsleves be studied by the scientific fraternity. So there must be other metabolic pathways that we are yet to dicover.