Why your size matters
One of my favourite books is Alice in Wonderland. As a child I was fascinated by the nonsense, as a diligent schoolgirl by the precision of the mathematics behind the words, now I re-read it mainly for the illustrations. If this is the wrong order to do things in, I blame Alice! It was also Alice who first opened my eyes to the question of size. Our size.

I am almost six feet tall. Whenever I am away from home for too long, my family and friends always exclaim “But you have grown taller!” as soon as they see me. I have not. I was precisely this tall when I was 14 years old (oh, so awkward!), and have stayed this height since (just right!). Life was less consistent for Alice. As she was tempted by delicious cakes, mushrooms and potions (can we blame her?), she shrank and grew throughout her travels beyond the rabbit hole. She almost drowned in her own tears, when she accidentally shrank too small.
The world feels different if you are smaller or bigger. Our experience of it is different. In fact, the world IS different.
I don’t mean this metaphorically. And nor did Lewis Carroll. For Alice the problem of size was very practical. Fitting through doors, or speaking to caterpillars was more convenient at the right size. Six feet is a little above average for a caucasian female, but any statistical difference within the Homo sapiens is negligible, when we compare ourselves with all the different life forms on our planet. A toddler and a NBA player are within the same size range, in the “biological size order of things”.

Despite my efforts with watermelons, I have to concede, that we are larger than the fruit we eat. We are smaller than the trees that bear them. We are larger than insects but smaller than whales.
We occupy a very precise size range in relation to our surroundings, which defines how we live and how we perceive the world. Some of this might feel self evident, but remembering what size we are in relation to other living things is imporant when we try to study both our life, and the non-human life around us. Our size defines both what we see (vision) and how we perceive the world (cognition).
We have evolved to recognise things that might kills us. A useful habbit. Our eyes move fast enough to spot a predator hiding in the bushes. They are incredibly sensitive to light. We see far enough to see a hurricane or a tsunami coming. The horizon may be just over 3 miles away, set by the curvature of the sphere we all stand on, but technically, we could see light from well beyond that. Vision scientists have estimated that we could make out the faint glimmer of a candle flame up to 30 miles away. The example of a candle is important because the light is so dim. We can see stars from many light years away, but they are much brighter than our candles.
We see a rainbow of colors. I am not a behavioral ecologist or a vision scientist, but I imagine part of the explanation is because they are beautiful, help us distinguish objects and attract the attention of a mate. Which is why flowers are such an effective way to communicate attraction! My favourite are peonies.
We could see a wider range of colours had our eyes evolved a bit further. Bees and many other insects can detect light in the ultra-violet. Your pet dog mainly sees the world in blue, and a little bit of grey and yellow. (I am sure that gets them an extra big hug today).

However, none of what we see of the world, is implicitly significant to its functioning or structure. What we see is only important to us, humans, trying to navigate our planet, which is orbiting a sun, in an insignificant corner of a small-ish galaxy. But I don’t need to remind you of the grandeur of the universe to highlight the insignificance of our size. My argument is simpler. Every living organism has its own reference scale. That is, depending on its size, things are either more or less important to its survival. In order to understand how things experience the world, we need to shrink or expand our thinking to their size. This is a lot trickier than it may seem. It is not easy to scale things. Life just gets curiouser and curiouser!
Take mosquitos for example. The average length of a mosquito is approximately 10 milimeters (or one centimeter). That means that if they all stood still for a second on each other’s shoulders, it would take 180 of them to make one of me. If you took 180 Elenas and got them to sand on top of one another, that would give us the Eiffel Tower, standing proud at 324 meters. Despite their frequent visits, it is safe to assume that to a mosquito I am not the Eiffel Tower. Mosquitos are not impressed by my height, because they can fly. What this means is that not only is size important, but so is behaviour. Relative distances shrink if you can move faster.
What about microbes? The mosquito example was entertaining, but insects are still very much within the scale of life that is relevant and accessible to our vision. It is much harder to grasp what the world is like to objects outside this comfort zone. A microbe is 1000 times smaller than a mosquito. That means that to a microbe, each mosquito is like two Eiffel Towers standing on top of each other’s shoulders. But do they care? Is this distance as impressive to them as two Eiffel towers would be to us, or are they like mosquitos in a human world?
The following questions are intriguing to scientists, and continue to receive attention, since the answers are largely unknown. How does the microbe perceive its surroundings? What other life is relevant to it, and in which size categories? Does a microbe interact with millions of other microbes, or only a few? My facebook network fluctuates around 800 connections. What is the social radius for a microorganism? How far do they travel? Is the evolution of swimming at these microbial scales the same as the evolution of flight in the air? As we make progress in studying microbial life, new thinking emerges in this area. This week, a research paper in Science magazine addresses some of these questions head on for microorganisms that live in the Ocean. I hugely enjoyed the read, and if you would like to find out more, click here for the link.
