(I’m going to have a highly controversial foray into the world of biology today, so do bear with me)

Could autotrophic humans bring an end to the need for chocolate cake, bacon and pasta? Or could there be something better in it for everyone?

In the world of biology, the huge range and diversity of Biota (living things) can be broadly broken down into two main groups, autotrophs and heterotrophs. An autotroph, like plants and many bacteria, are organisms that can produce complex organic compounds, such as carbohydrates, fats, and proteins from simple substances present in its surroundings, generally using energy from light (by photosynthesis) ,and carbon dioxide and water from the air and soil . Heterotrophs, like you and me, on the other hand can’t make these complex molecules, and so need to ingest them, most usually through the eating of many delicious foods. But in today’s world, where space is at a premium and food prices are sky rocketing, surely there are better ways of gaining energy from the world, rather than eating its flora and fauna? What if, like plants, we had evolved differently and could create our own energy and proteins using chloroplasts in our skin? For one, we would most probably all turn green from the amount of chlorophyll, but what about the practical side of it? To start, could we actually survive on nothing but sun light, carbon dioxide and water? And what effects would this have on our environment as land use and populations move and change?

Well, first, let’s have a look at the maths (I’m going to make a point here as many people have brought it up with me; ALL of these numbers are optimal numbers, they don’t take into account bad weather, questionable dress sense or how well aligned with the sun you are, they are simply the best and most favourable estimates for this strictly hypothetical experiment). First things first, let’s have a look at our subject; an average adult British male has a usable surface area of about 1.88m2. This is actually not a lot, but we’ll talk about that later. Now, the average solar power absorbed by the entire earth’s surface is roughly equivalent to 164 petawatts, so the amount absorbed by your average male of 1.88 m2 is in the order of 564 Watts (about half a toasters worth of power). So over the course of the day, with six hours of strong, good quality sunlight, our subject would absorb nearly 12,000,000 joules of energy. This does sound like a lot, but do remember, all this solar energy has to go through the chloroplast first, before becoming usable energy. Chloroplasts are deceivingly inefficient, only turning around 6% of the absorbed light energy into actual, usable energy. For plants and bacteria this is more than enough but for humans this means only 720,000 joules of that glorious sunshine becomes usable energy. This value is far short of our bodies recommended energy intake of 10.5 million joules, in fact it’s just under 7% of what we need.

So that’s a no then to running on sunlight. The problem is that humans just aren’t big enough; we have a lot of mass (and therefore a lot of things that need energy) and not much surface area to go along with it. This, however, is the opposite for plants, who have very little respective mass, yet are given a very large surface area due to all their leafy bits.

But it’s not all doom and gloom. Although 7% doesn’t sound like much it all adds up. Just think 13,800,000 km2 of the earth’s surface is taken up by crops and farmland, 7% of this is nearly 1 million square kilometres, an area about the size of Egypt! This land could be put to use as housing to ease the worlds crippling over population and lack of space, or even as extra public parks and spaces.

But what if we kept this land as farm land? What if we used it to a better purpose? 1,000,000 km 2 of farm land equates to a lot of food. If we take the example of wheat, the world’s staple food and one of the most important grains in production. In the year of 2010 the world wheat production was 651 megatons. If 7% of this was going spare, 45.5 megatons, we would have enough grain to feed nearly half a billion people (assuming average consumption of 100kg per annum).  But then again, there are around 1 billion malnourished people in the world, so would this 45.5 megatons of wheat stretch that far? Let’s look at the human body’s most essential micronutrient, iron. Iron is needed to allow the oxygen we breathe in to bond to the haemoglobin in our blood, without which, we simply wouldn’t be able to live. Iron deficiency is defined as having less than 55% of our recommended daily intake of iron. So if we assume that less than 55% of any food stuff equates to malnourishment, or a food deficiency, our ½ billion people worth’s of food could feed every malnourished child, adult and homeless person in the world (within the realms of statistical error).

To conclude, the idea of individuals running off of sunlight and chloroplast may not be viable, but if we add up the small positives, they make a very large difference

Alex Davis

Sources:

http://www.who.int/en/

http://www.fao.org/

http://en.wikipedia.org/wiki/Chloroplast

http://en.wikipedia.org/wiki/Solar_energy

A calculator

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