What is the nature of ethological theory? What are some contributions and criticisms of the theory?

Ethology and its associated theories all stress the importance of the inter-relatedness of biology and behavior. The main gist is that behavior is strongly influenced by biology. Additionally, the biological behaviors that result are often tied to "critical periods." An example that gets used quite often to illustrate the theory and critical periods is the imprinting that occurs with baby geese. These goslings are born with the natural, biological ability to develop an attachment to the first thing(s) they see. It could be the mother goose, a human, or a even a child's toy. That biological imprinting will then affect the behavior of the goslings. The theory does have some Darwinian support because it shows how biological behaviors are tied to evolutionary changes. Additionally, ethology supports the idea that an animal's (or person's) personality/behavior is dependent on both the biological nature and environmental nurture.
http://www.personalityresearch.org/papers/pendry.html