Recent research from Vanderbilt University demonstrating that microbes in the gut of animals can substantially influence selection and thus evolution, is interesting. It implies that the outcome of evolution is based on a constrained optimization taking into account the characteristics and needs of multiple organisms in a single matrix. The interesting question is what dominates the process and how it has shaped evolutionary history.
Single cell organisms, amazingly robust and extremely flexible, have been dominating the Earth ever since they arrived, possibly hitching a ride on an asteroid. They shaped the environment to suit them and fundamentally changed the course of the blue planet. They meticulously designed carriers for them to survive in harsh conditions and thrive invisibly. Nothing less could have been expected of a species that travelled through interstellar space, billions of years ago.
Their hosts, complex and customized carrying boxes for this remarkable species are left with sheer astonishment as they study these superior biological entities.