Why yawning is contagious

This Straight Dope article[1] from twenty-five years ago attempts to answer the same question, with the answer being mostly "we don't know". However, some of the "maybes" in this article are cited in the video as fact.

One thing the article notes, however: "We merely observe that whatever yawn-inducing conditions prevail for you also apply to your friends. If you're out late in some crowded dive, you're probably all tired, all warm under the collar, and all breathing the same stale air. You're probably all on the verge of a yawn, too, and the power of suggestion from seeing one person do it is enough to push everybody else over the edge.

Adults rarely catch a case of the yawns from a child or animal, which tends to corroborate this idea. Children usually have different sleep schedules and respiration rates from adults, so you would expect them to yawn at different times."

The "everybody else is probably tired, hot, breathing the same air, etc" always sounded convincing to me. It isn't that yawns are contagious, just that the conditions which cause them often exist for others around you too. I'm wondering what the vsauce guy would say to that. Does anybody know if the "adults rarely catch a case of the yawns from a child or animal" has held up to scrutiny in the last 20 years?

[1]http://www.straightdope.com/columns/read/533/why-are-yawns-c...

Barely read the title, saw the link to a video, pictured an image in my head of someone yawning and others copying ... had to yawn myself.