Photosynthesis? I think this is right
Answer:
As we can see from the graph above, brightly colored guppies would only survive in environments without predators, as they have worse camoflague thanks to their bright tail fins. In an environment with predators, guppies with plain/not brightly colored tail fins would survive better, seeing how while even placed in the predator's sight the guppies were less likely to be attacked when not brightly colored.
Embryologist study embryos because Embryology is central to evolutionary developmental biology ("evo-devo"), which studies the genetic control of the development process (e.g. morphogens), its link to cell signalling, its roles in certain diseases and mutations, and its links to stem cell research.