After the earth cooled below the boiling point of water about 4 billion years ago, weather became possible. Less than half a billion years ago, a few land animals were the first to experience it.
We have inherited a more profound response to day-night cycles. One virtue of such circadian rhythms is that they synchronize a lot of interrelated events in the body, so that we digest our food before we need to sleep without a trip to the bathroom. Paleomom likened this to a conductor bringing all the instruments in a symphony into harmony.
Some folks take this too far and attribute a controlling influence to stars, planets, and the moon. For centuries humans have believed that people behave abnormally when the moon is full. Yet even writers who regard some correlations between our behavior and lunar cycles admit that there is no mechanism for connecting the two.
We’re all impressed by surprising coincidences. But real-life rarities happen every day. They turn up among twins and in lots of other observations. Before we start humming the theme music from Twilight Zone, we should consider a mental quirk called apophenia, or what Shermer calls patternicity.
Seeing Jesus or Elvis or Che Guevara in a piece of toast sets us wondering whether it could be more than just chance. (Answer: Probably not) It’s not a bad quirk, in my opinion. It’s usually the start of our search for causation, even for non-statisticians. It’s astonishingly hard to prove causation in the brain.
Happy coincidences are scientific gold to the alert researcher, like Pasteur with his bread mold or Pavlov noticing salivation. We have to guard against misplaced faith.
We’re all impressed by surprising coincidences. The question we have to answer is whether a lightning strike of coincidence that accompanies a decision is a sign or a random surprise. Why do unexpected correlations make us think “What are the chances?” and suspect ulterior causes? We reflect that random events can’t lead to rare outcomes; but they do, and of course they’re noticeable. They impressed the heck out of Carl Jung. It was Carl Jung who decided that they pointed to an underlying synchronicity that organized our experiences
Even if you’re good at judging correlations…it helps to remember that correlation is an observation, while causation is an inference. It matters whether you’re a skeptic or a believer and a happy consumer of arguments that wind like the Mississippi.
BIO: We should celebrate the discoveries about biological clocks that won three researchers a Nobel prize. Their work gives us a window on how genes set our clocks, while jet lag hands us the result in personal experience. But what happens between genes and jet lag? The overall story starts with sleep and finishes with proteins under genetic control. That’s good, but what goes on in the brain?
With the help of an excellent diagram from the jet lag article, shown at bottom, let’s begin with retinal ganglion cells. You have been studying the ones that channel activity from the rods and cones, but there’s another kind that sense light directly. These photosensitive retinal ganglion cells send signals about day-night cycles to the hypothalamus along the retinohypothalamic tract, in particular to the suprachiasmatic nucleus or SCN. Daylight makes the SCN tell the pineal gland to stop making melatonin, which would put us to sleep. This light-entrained system works fine for most of us, although people who live near the poles rely more on the intrinsic gene-generated rhythms, because who wants to stay awake all summer and sleep all winter?
How do blind people maintain normal circadian rhythms? They have normal light-dark cycles because of a visual sense that we are not aware of consciously.
There are retinal ganglion cells that act as photoreceptors for our daily rhythms. They use a special pigment called melanopsin to absorb light. Instead of forming an image, they pass on information about the timing of light and dark to the suprachiasmatic nucleus in the hypothalamus along a phylogenetically ancient pathway. In other words, this stimulation probably doesn’t reach the lateral geniculate nucleus by the usual visual pathway (optic nerve, optic tract), yet in some people the information may eventually reach the visual cortex with rather baleful results.
The retina is mostly clear–transparent–except for blood vessels and the photopigments in the rods and cones, which light reaches only after it has already passed through most of the retina. So light can reach these ganglion cells almost undiminished. The ganglion cells also receive some input from rods and cones, but this influence is still not understood well.
PSYCHO: However much we might need to synch processes that depend on sunlight, culture further entrains our rhythms needlessly. We might not need to work the usual shifts. Standardization and uniformity are cultural values (of 19th-century socialism), not evolutionary imperatives. In fact species depend on genetic variation to avoid extinction!
(You may object that people who work on personal schedules will still be working cyclically, and that’s OK. If a rhythm is meaningful, use it. The question I’d ask is whether rhythms, like soldiers marching in synchrony across a bridge, might prove inefficient in the end. But maybe we just can’t help it.)