This research reveals how certain mushroom species permanently lost their ability to decompose dead plant matter as they evolved to form beneficial partnerships with living plants. This evolutionary change represents a point of no return – once these fungi became dependent on their plant partners, they could no longer go back to living independently. Impacts on everyday life: – Helps explain why many forest mushrooms only grow in association with specific trees – Demonstrates how organisms can become permanently dependent on their partners in nature – Provides insights into the evolution of cooperative relationships between species – Improves our understanding of forest ecosystem functioning – Could inform cultivation practices for economically important mushroom species