The source for the information was David Weinberger's Too Big to Know, in which he argues that "the Internet has profoundly changed what it means to be a fact, to be true, or to be known."
This new knowledge about knowledge immediately manifested itself for me, when for about the gazillionth time at the gym, I wondered while doing my sit-ups on an abs bench: "Why do I keep yawning?" and for the first time remembered to actually search the Internet for "the facts" on that once I got home.
LIVESTRONG.COM's article, Excessive Yawning While Exercising, says, "Yawning is one way your body responds to a lack of oxygen -- the long, deep breath associated with a yawn increases the oxygen supply to your blood via your lungs."
Greatist.com's article, FAQ: Why Do We Yawn When Working Out?, says, "Yawning was long thought to be an indication of low oxygen levels in the blood, but scientists have since dispelled that theory.  Yawning: no effect of 3-5% CO2, 100% O2, and exercise. Provine, R.R., Tate, B.C., Geldmacher, L.L. Department of Psychology, University of Maryland. Behavioral and Neural Biology. 1987 Nov;48(3):382-93. [↩]
And finally, WebMD.com notes in its Why do we yawn? article no less than six theories, none of which have been definitely proven:
- Yawning brings in oxygen to counteract increased amounts of carbon dioxide in the blood.
- Yawning is the body’s way of controlling brain temperature.
- Yawning satisfies the need to stretch your muscles.
- Yawning is associated with nervousness.
- Yawning helps you stay alert.
- Yawning is a sign of dominance.
That entry also says that "some scientists are now claiming that yawning is a sign of sexual attraction rather than a desire to sleep."
And it concludes with, "We may never know exactly why we yawn or why dogs, monkeys and all other vertebrates — with the inexplicable exception of the giraffe — do it either. Perhaps giraffes do yawn, and we just haven’t (or can’t!) observe it.
I'm gonna stick my neck out and just declare, "I yawn, therefore, I am... not a giraffe."