Let's throw a mouse, a dog and an elephant from a skyscraper onto something soft let's say a stack of mattresses the mouse lands and is stunned for a moment before it shakes itself off and walks away pretty annoyed because that's a very rude thing to do, the dog breaks all of its bones and dies in an unspectacular way and the elephant explodes into a red puddle of bones and inside and has no chance to be annoyed. Why does the mouse survive but the elephant and dog don’t? The answer is size is the most underappreciated regulator of living things size determines everything about our biology how we're built how we experience the world how we live and die. It does so because the physical laws are different for different sized animals. Life spans seven orders of magnitude from invisible bacteria to mites, ants, mice, dogs, humans, elephants and blue whales.
Every size life in its own unique universe right next to each other each with its own rules upsides and downsides. We'll explore these different worlds in a series of articles. Let's get back to the initial question why did our mouse survive the fall? Because of how scaling size changes everything a principle that we'll meet over and over again. Very small things for example are practically immune to falling from great heights because the smaller you are, the less you care about the effect of gravity. Imagine a theoretical spherical animal the size of a marble, it has three features its length, its surface area which is covered in skin and its volume or all the stuff inside it like organs, muscles, hopes and dreams. If we make it 10 times longer say the size of a basketball the rest of its features don't just grow 10 times its skin will grow 100 times and its insides or its volume grows by 1000 times. The volume determines the weight or more accurately mass of the animal the more mass you have the higher your kinetic energy before you hit the ground and the stronger the impact shock the more surface area in relation to your volume or mass you have the more the impact gets distributed and softened and also the more air resistance will slow you down an elephant is so big that it has extremely little surface area in ratio to its volume, so a lot of kinetic energy gets distributed over a small space and the air doesn't slow it down much at all, That's why it's completely destroyed in an impressive explosion of goo when it hits the ground.
The other extreme insects have a huge surface area in relation to their tiny mass so you can literally throw an ant from an aero plane and it will not be seriously harmed but while falling is irrelevant in the small world, there are other forces that are harmless for us but extremely dangerous for small beings like surface tension which turns water into a potentially deadly substance for insects. How does it work? Water has the tendency to stick to itself. Its molecules are attracted to each other through a force called cohesion which creates a tension on its surface that you can imagine as a sort of invisible skin for us, this skin is so weak that we don't even notice it normally. If you get wet about 800 grams of water or about one percent of your body weight sticks to you. a wet mouse has about three grams of water sticking to it which is more than ten percent of its body weight. Imagine having eight full water bottles sticking to you when you leave the shower, but for an insect, the force of water's surface tension is so strong that getting wet is a question of life and death. If we were to shrink you to the size of an ant and you touch water it would be like you were reaching into glue it would quickly engulf you, its surface tension too hard for you to break and you drown. So, insects evolve to be water repellent for one their exoskeleton is covered with a thin layer of wax just like a car, this makes their surface at least partly water repellent because it can't stick to it. Very well many insects are also covered with tiny hairs that serve as a barrier. They vastly increase their surface area and prevent the droplets from touching their exoskeleton and make it easier to get rid of droplets to make use of surface tension.
Evolution cracked nanotechnology billions of years before us, some insects have evolved a surface covered by a short and extremely dense coat of water repelling hair, some have more than a million hairs per square millimeter when the insect dives underwater air stays inside their fur and forms a coat of air water can't enter because the hairs are too tiny to break its surface tension but it gets even better as the oxygen of the air bubble runs out, new oxygen diffuses into the bubble from the water around it while the carbon dioxide diffuses outwards into the water and so the insect carries its own outside lung around and can basically breathe underwater thanks to surface tension.
This is the same principle that enables pond skaters to walk on water by the way tiny anti-water hairs, the smaller you get, the weirder the environment becomes at some point even air becomes more and more solid. Let's now zoom down to the smallest insects known about half the size of a grain of salt. Only 0.15 millimeters long, the fairy fly, they live in a world even weirder than other insects for them air itself is like thin jello, a syrup-like mass surrounding them at all times movement through it is not easy flying on this level is not like elegant gliding, they have to kind of grab and hold onto air so their wings look like big hairy arms rather than proper insect wings, they literally swim through the air like a tiny gross alien through syrup things only become stranger from here on as we explore more universes of different sizes. The physical rules are so different for each size that evolution had to engineer around them over and over as life grew in size in the last billion years so why are there no ants the size of horses? why no elephants the size of amoeba? why? We'll discuss this in the next part.
0 Comments