When we think of a nest, we think simply of a natural piece of construction. A bird gathers together twigs and stems and leaves and assembles them into a shelter for its eggs. We don’t think much about the plants it uses. They’re just. Mutualistic symbioses are considered to evolve from parasitic relationships. Vertical transmission, defined as the direct transfer of infection from a parent organism. Evolution home: Predator-Prey Relationships….