Imagine a clutch of frog eggs glued to a leaf above a tropical pond. The eggs are in their final third week of development. If you looked at the eggs you could see the tiny tadpoles inside, getting ready to be born within a few days. A hungry snake spots the eggs and moves in for a major meal and chomps down on the edge of the egg mass. You might feel that this is the end for the tadpoles, because the snake will certainly eat this helpless mass of babies within a few minutes. Not so!

As soon as the snake makes its attack, the babies inside the eggs start to wiggle frantically, breaking out of their egg casings. They are not fully developed, but they are far enough along to survive, and as soon as they get out of the egg casings they fall to the pond below and finish their development.

Scientists studying this behavior have found that if they mimic the frequencies produced when the snake attacks the eggs, they can duplicate this egg behavior in the red-eyed tree frog. Using other frequencies produces no response from the tadpoles. How can a baby tadpole know how to detect the frequency of an attacking snake and make a response to that frequency?

Karen Warkentin who has been studying this response at Boston University says that her research shows "how well-developed an embryo's decision making can be." It is certainly a wonderful example of the design built into living things that allows them to survive in a world of predators.

Reference: Natural History, July/August 2005, page 13.