I find myself regularly experiencing jet lag that I take for granted that this is yet another modern discovery. Humans have been traveling great distances ever since, well, we've been human. From an evolutionary standpoint, we seem to be built for it: long legs, endurance, and the ability to sweat.

We've only been traveling across enough time zones too fast for our internal body clocks to adjust since the advent of jet travel. According to this fascinating article from the Smithsonian, the term "jet lag" wasn't mentioned until 1966. But it wasn't until 1980 that a true scientific study about it was done.

“In 1980, NASA (in collaboration with the FAA, and at the request of Congress) established a program to further study the problem. The NASA Ames Fatigue/Jet Lag Program set out “to collect systematic, scientific information on fatigue, sleep, circadian rhythms, and performance in flight operations.” Researchers determined that if the average biological clock were allowed to run at its natural rhythm, “the average internal biological clock would actually have a cycle slightly longer than our 24 hr. day, about 25 hr…. Therefore, when traveling westward, the circadian day is lengthened (or delayed) and promotes adjustment to the new time zone. Conversely, when flying eastward, the circadian day is shortened (or advanced), contrary to the natural tendencies of the internal clock.””

— Rebecca Maksel, Smithsonian Air & Space Magazine

There are a couple amazing facts from this paragraph:

Once upon a time, Congress actually expressed interest in science and funded two agencies to establish a program to study this phenomenon.
It wasn't until 1980 that we discovered that the average human biological clock ran on an almost 25 hour daily cycle.

Go read the rest of the article to learn a few more interesting things about jet lag.

I've had the opportunity to travel internationally many times over the past few years as part of my job, and I have developed some simple techniques for dealing with jet lag:

Avoid red-eye flights. I used to be able to do this gracefully when I was younger, but as I've aged, I try to avoid these as much as possible.
Stay hydrated and eat normal, healthy food as much as possible. Generally a good rule to follow regardless, but the temptation to eat lots of crappy airport & airline food is very strong.
When you arrive at your destination, do everything you can to stay awake such that you can go to bed at close to a "normal" time on your first day; if you give in and fall asleep in the middle of the day, getting adjusted will be significantly more difficult.
If you need to, use melatonin or some other (legal) sleep aid to enable you to not only fall asleep but stay asleep for something close to a normal night's sleep.
Close the blinds, draw the curtains, or use an eye mask to block light when you're sleeping.
Try to stay disciplined about going to bed at a normal time for the first couple nights to establish a good start – your body will adjust more quickly that way.
Use an alarm clock to wake you up at a normal time – if you sleep in way too late, you're just delaying your body's ability to adjust. Plus you'll lose some valuable vacation/tourist/work/fun time.

I'm currently suffering from significant jet lag (16 hour time difference between San Francisco and Tokyo – if I lived in San Fransokyo I wouldn't have this problem), but I'm trying to follow my own advice so I really need to get some sleep now. Good night.