While research with the frog may be complex and require years of study, the frog is a great animal for explaining to children science and evolution! A teacher and parent guide....
The frog evolved, as other animals did, from the ocean, from there they formed their "niche." The frog "niche" became muddy ponds and banks of streams. The frog became a "species" because it thrived in the "muck." It built defenses against disease and bacteria present in that "niche." Of course it had to hop and swim to escape predators, and get food! So the frog could hop into the water, and get food with each jump! Clever huh? So as time went on, frogs were able to survive, even thrive, because their skin developed resistance to "pathogens." While "bacteria" or "pathogens" can be bad, they can also be good. A "pathogen" will help an animal thrive if it has "resistance" to it. So this is why we use the frog in our research! Because it has evolved to have resistance to bacteria and "pathogens" in the muck! It is easy for us to keep in our labs and even if it does have some bacteria on its skin, its skin is protecting it and it does not affect our research. It usually does not get sick and die. Could we say the "dirt" and bacteria were a good thing, helping the frog become what it is today all over the world, with many different species and niches but still a "frog?" Well, yes! And so with many thousands of years of frog evolution they been successful because of their ability to protect themselves against bacteria, and pathogens. It may even be a main feature of a frog, like language and reason are for humans! Another interesting thing about frogs: if one does get sick it usually does not infect other frogs. We as scientists like that about the frog because we like to keep our frogs happy! However, frogs appear to have another layer of protection or "adaptation" that keeps them from spreading disease frog-to-frog. We observe frogs huddle together: we theorize that they like to huddle to "appear bigger" (or hide together) so another animal will not attack them! So the resistance they have to passing disease and fighting bacteria also allows them to huddle together. In this way the protection against bacteria frogs have "evolved" allows frogs to huddle together as a protective adaptation, and warmth, as more predators evolved around them!
Rob's niece and nephew netting a frog