This study seeks to extend our understanding of how various conditions influence the trajectory of co-evolutionary relationships between two seemingly symbiotic populations. To that end, we trace the co-evolutionary path of medical tech start-ups and venture capitalist (VC) investors in the US from 1980 to 2017 and examine the impact of the tech-bubble, government supports, and industry maturity on their co-evolutionary relationship. We found support for the existence of a deviation-amplifying relationship between previous growth and current growth of new medical tech ventures and a deviation-countering relationship between previous exit events and growth in new medical tech ventures. However, contrary to expectations, we found a deviation-countering, or competitive, co-evolutionary relationship between growth in the number of new VC investors and growth in the number of new ventures instead of a symbiotic one. Our findings suggest that co-evolutionary relationships between two seemingly symbiotic populations may actually become deviation-countering in the presence of other stronger deviation countering reciprocal causal processes.