Thousands of organisms (including rats and humans) biosynthesise dimethyltryptamine, and to me at least, that's not the interesting part, the part I find more interesting is that of the tens (hundreds?) of thousands of plant species in the Amazonian jungle, they found the two that work together, oral DMT isn't normally active, as it's broken down by monamine-oxidase, one of the plants in Ayahuasca is an inhibitor of this enzyme.

A similar story exists around the discovery of LSD (LSD-25 was just one in a sequence of lysergic asid that was synthesised by Albert Hoffman) – it was years later that Hoffman decided to revisit the compound, thinking... "There must be something there..."

It's all likely coincidence, but there exists (especially with plants, such as those that produce DMT, and Psilocybin) that we have evolved together.