Answer: Livestock

It would be easy to assume that the first hot air balloon passengers were the inventors of the hot air balloon, but no. In September of 1783, when French paper manufacturers and inventor brothers Joseph-Michel and Jacques-Étienne Montgolfier sent their first “passenger capable” hot air balloon aloft, they were not in it (an earlier test flight occurred in June).

Neither were any of the dignitaries and aristocrats that had gathered to see the launch nor, for that matter, was there even a human being aboard the balloon. Why no humans? High altitude flight of any sort had not been tested in any way and there was concern that it could injure or kill the passengers.

Although the King of France offered some prisoners as less-than-willing test subjects for the first manned experimental flight, the brothers declined and instead attached a basket containing a sheep, duck, and rooster. The duck was included, rather practically, as the control group under the presumption that the high-flying duck would have no issue with the altitude. The test was a success, lasted eight minutes, and the balloon flew roughly 2 miles with a safe landing. The next two tests (one tethered and one not) were conducted with human volunteers and over the next few years rapid advances in hot air balloon design led to the hot air balloon becoming a viable (albeit slow) method of human flight.