16 Jun ’07

The impact of a sunset

A sunset just passed by, and it is pretty. We've all seen thousands of sunsets (mainly in the evening), and for a moment I wonder what biological effects a sunset still has on human beings. Wikipedia has remarkably little to say on the topic of circadian rhythms or melanopsin-containing ganglion cells, which are the photosensitive cells in your eyes (not rods or cones) that are responsible for these nonvisual effects of light on your body.



There are several known biological reactions that the specific light frequencies of a sunrise (and presumably sunset) has on your body. Our whole evolutionary history has had its rythem dictated by the coming and going of the sun, day in day out. Even now, you are using sunrises and sunsets to adjust your circadian clock to match the earths', and this internal clock is changing your hormone levels and doing all sorts of things.

Further back into the past, your whole evolutionary history (from the first lightsensitive bacteria, floating around in the ocean and muddy pools, up to your life now), you have been sensitive to the cycle of day and night.. That is a staggering 4 billion years. All this time your eyes / antenna / photosensitive organels have been observing sunsets.

A recent article (Mar 2007) in the journal of physiological anthropology quotes some of the studies currently being performed to study the influence these cells have on human beings: longterm effects as Seasonal Affective Disorder (SAD), sleep disorders, depression, senile dementia are candidates for light therapy. More interesting to me are the direct effects of light.. just an increase in the quantity wakes people up, immediately affecting behaviour and increasing cognitive performance.

It will probably be a few decades ere science knows what watching the sunset does to a human being. Up till then, I'll just enjoy the feeling that comes over me when I do.