15. Photon detectors
Your eyes are very sensitive, able to detect just a few photons of light. If you take a look on a very clear night at the constellation of Andromeda, a little fuzzy patch of light is just visible with the naked eye. If you can make out that tiny blob, you are seeing as far as is humanly possible without technology. Andromeda is the nearest large galaxy to our own Milky Way. However, “near” is a relative term in intergalactic space — the Andromeda galaxy is 2.5 million light years away. When the photons of light that hit your eye began their journey, there were no human beings. We were yet to evolve. You are seeing an almost inconceivable distance and looking back in time through 2.5 million years.
16. Sensory tally
Despite what you’ve probably been told, you have more than five senses. Here’s a simple example. Put your hand a few centimeters away from a hot iron. None of your five senses can tell you the iron will burn you. Yet you can feel that the iron is hot from a distance and won’t touch it. This is thanks to an extra sense — the heat sensors in your skin. Similarly we can detect pain or tell if we are upside down.
Another quick test. Close your eyes and touch your nose. You are not using the big five to find it, but instead proprioception. This is the sense that detects where the parts of your body are with respect to each other. It is a meta-sense, combining your brain’s knowledge of what your muscles are doing with a feel for the size and shape of your body. Without using your basic five senses, you can still guide a hand unerringly to touch your nose.
17. Real age
Just like a chicken, your life started off with an egg. Not a chunky thing in a shell, but an egg nonetheless. However, there is a significant difference between a human egg and a chicken egg that has a surprising effect on your age. Human eggs are tiny. They are, after all, just a single cell and are typically about 0.2 millimeters across — about the size of a printed full stop. Your egg was formed in your mother — but the surprising thing is that it was formed when she was an embryo. The formation of your egg, and the half of your DNA that came from your mother, could be considered as the very first moment of your existence and it happened before your mother was born. Say your mother was 30 when she had you, then on your 18th birthday you were arguably over 48 years old.
18. Epigenetic influence
We are used to thinking of genes as being the controlling factor that determines what each of us is like physically, but genes are only a tiny part of our DNA. The other 97 percent was thought to be junk until recently, but we now realize that epigenetics — the processes that go on outside the genes — also have a major influence on our development. Some parts act to control “switches” that turn genes on and off, or program the production of other key compounds. For a long time it was a puzzle how about 20,000 genes (far fewer than some breeds of rice) were enough to specify exactly what we were like. The realization now is that the other 97 percent of our DNA is equally important.
19. Conscious action
If you are like most people, you will locate your conscious mind roughly behind your eyes, as if there were a little person sitting there, steering the much larger automaton that is your body. You know there isn’t really a tiny figure in there, pulling the levers, but your consciousness seems to have an independent existence, telling the rest of your body what to do.