The phrase "various theories" refers to multiple different ideas or explanations that people have come up with to understand a particular topic. Full definition
In the 1970s, he put forward various theories about population levels. (climatedepot.com)
There are various theories on choosing a puppy, from grabbing the first one you see to spending hours administering the puppy aptitude test to every puppy in a litter. (raisingspot.com)
The bright spots have been a subject of much discussion, with various theories as to how they formed. (americaspace.com)