Today I want to introduce to you a few hypotheses about what Jessie could be. Notice I don't use the word "theory," which in the scientific world means that we would have a lot of solid evidence and, according to Karl Popper at least, could find ways to falsify it. The Society does in fact have a theory, or at least a hypotheses with some strong evidence, but I want to throw out all the ideas before we give away what we think.
1. A giant turtle or tortoise
This is not a bad hypothesis. There are known giant tortoises in the world (mostly in the South Pacific), and they can get pretty big (600 lbs, 4 feet long). They are non-agressive and somewhat reclusive, which would explain why no one has yet to find it in Jamaica Pond.
On the other hand, no tortoises of similar size have been reported in North America. In addition, our average Jessie Estimated Length is 8 feet, almost double the size of the largest known tortoise, even in the fossil record. It's also unlikely they could survive the winter.
2. An alligator or some other lizard
Back in 2003 they found an alligator in Jamaica Pond. It was a young one, about 2 feet long, and they estimate it had been released by an owner who didn't want it anymore. Given that Jessie is primarily aquatic, if it were a non-tortoise reptile it would most likely be in the alligator or crocodile class.
However, the pattern of non-agression of Jessie, as well as the fact that winters once again would prove fatal, make the alligator theory fairly unlikely.
3. A Plesiosaur
As exciting as it would be to have our very own Loch Ness Monster right here in JP, I think this one is particularly unlikely. The pond it just too small for a giant marine dinosaur. Not only would someone have seen it, they would have seen it at eye-level when looking out the window of the 10th floor of the Perkins Towers.
4. A Manatee
Definitely a possibility. They are the right size, live in fresh water, actually exist, are non-agressive herbivores, and it's possible somehow one got up here. Howevever, many Jessie sightings or Jessie evidence occurs outside the water, in the woods -- places a manatee wouldn't go (as far as our current understanding goes).
5. A Giant Beaver
The giant beaver, Castoroides ohioensis, went extinct about 10,000 years ago, along with a host of other large mammals, left over from the last Ice Age. Or did it? These beavers (not closely related to modern beavers) grew to be over 8 feet long, were primarily herbivores, and certainly lived in the Boston area. They pop up in First Nations / American Indian legends in Central Massachusetts and Nova Scotia. Not much is known about their lifestyle, though they are thought to not have been dam builders because the didn't have the proper teeth for that task.
6. Unknown unknown
Let's face it, if we are honest with ourselves, we will have to admit that we have never exhausted all options. Jessie could be an alien, a creature unknown to the fossil record or science, an accumulation of the psychic energy of tens of thousands of Jamaica Pond visitors, who knows? But I think these things are unlikely. True, I must allow the possibility, but since we are sitting on, I don't know, 160 years of evidence to the contrary, I would like to confine Jessie to the realm of what is most likely.