Humans have always studied animal behavior informally. Animal behavior informs behavioural ecology = study of how organisms make decisions that influence their survival and reproductive success. Ethology = study of animal behavior in natural environments from an evolutionary prospective. Gene products (i. e. enzyme) can affect behavior by starting a series of gene environment interactions that underlie development of behavioural mechanisms. Biologists study the ways both genes and the environment. Nature vs. nuture issue is not about whether genes or environment influence behavior how are both involved. Chemicals that mimic hormones especially estrogen and this may be having major consequences suggests that the build of these chemicals in feminization of various animal species and decreased quality and quantity of sperm in humans. Some behaviours expressed only in certain conditions, where an object, events or condition is required to elicit a behavior (=releaser or sign stimulus) Sequence of unlearned, innate behaviours that is unchangeable.