MANY instincts are so wonderful that their development will probably appear to the reader a difficulty sufficient to overthrow my whole theory. [page 317] In this episode of Discovering Darwin we covered Darwin's chapter on Instinct and how Chuck attempted to explain how animals exhibit complex behaviors that are not learned. More importantly Darwin was trying to outline how behaviors could evolve in the same way he explained the evolution of physical traits. It is not too difficult to study the evolution of physical traits because we often have fossil evidence of their transformation. Last episode we discussed the evolution of whales and the plethora of fossil evidence that has allowed researchers to reconstruct the evolution of the terrestrial ancestor of whales to the streamlined marine mammals we see today.  Behaviors are harder to imagine through the lens of natural selection because we can only see those behaviors that are exhibited by extant (living) organisms and behaviors can evolve much faster than physical traits. Cultural evolution can allow individuals within their lifetime to adopt a new behavior that they learn from others. One of the wonderful examples of this is dolphins using a sponge to protect their rostrum (beak) as they hunt for prey in coral structures. They can pass this idea on to other dolphins and you can track the rapid transmission of this behavior through a population. Picture from http://www.livescience.com/21989-dolphin-sponge-tools-culture.html Darwin was not interested in learned behaviors in this chapter but he was interested in behaviors that are known at birth or at specific developmental times in the organism's lifespan. Darwin called these behaviors instinct. In exploring this idea Darwin focused on three major examples of innate/instinctual behaviors: 1. Cuckoos and their behavior to dump their eggs in other birds nests. 2. "Slave making" ants species which capturing of other ant species to become sources of forced labor in their own colonies. 3. Honey bees and their complex, mathematically efficient, honeycomb making behavior. Cuckoo Cuckoos exhibit a behavior known as "brood parasitism" where they lay their eggs in the nest of a host species and leave the eggs to be incubated and hatched by the host. The host also raises the cuckoo baby as their own until it is strong enough to fledge from the nest. Below is a dramatic photo showing the poor host Reed Warbler dutifully feeding the ginormous common cuckoo (Cuculus canorus) nestling. "Reed warbler cuckoo" by Per Harald Olsen - Own work. Licensed under CC BY-SA 3.0 via Commons - https://commons.wikimedia.org/wiki/File:Reed_warbler_cuckoo.jpg#/media/File:Reed_warbler_cuckoo.jpg You may wonder why the Reed warbler does not recognize the cuckoo offspring is not their own offspring? What you are really asking is why has the Reed warbler not evolve the ability to recognize its own offspring from another species? If you were switched at birth in the hospital, do you think your mother would know? What ways do we know our offspring are actually ours? Only through hospital tagging or non-interrupted contact are we to "know" the offspring we have are the ones we gave birth to.  Why have we not evolved an ability to recognize our own offspring? Probably because there has not been a selective advantage to recognize our offspring because over evolutionary time it has been rare for humans to be in a situation where we must recognize our newborn from other unrelated newborns. Since that ability is rarely useful, selection has not favored it in our species. In the same manner, birds that nest individually associate those eggs in their nest as being their own. Recognition has not evolved because there is little selective advantage for that ability. However there are birds that do exhibit an amazing ability to discern their own specific offspring among a throng of others. Colonial nesting birds like albatross and penguins have an unerring abilit