Within experimental psychology there came a reaction to behaviorism in what we now call cognitive psychology. In contrast to behaviorism, cognitive psychologists start with the assumption that individuals (humans and other animals) have a mental life that can be investigated. For instance, Skinner (1957) maintained that language development in children was a learning process, where responses (i.e. uttering certain sounds) were reinforced. The great American linguist Noam Chomsky (1959) wrote a lengthy and highly critical review of Skinner’s book on language development, in which he suggested that language acquisition is not a case of instrumental conditioning, but the development of certain cognitive mechanisms, the so-called universal grammar

Niko Tinbergen  outlined the four major
questions in the study of animal behaviour, namely causation, development,
function (Tinbergen called this ‘survival value’) and evolution. As he readily
admitted, Tinbergen was not very original, as three of these questions
(causation, function and evolution) had already been put forward by the British
biologist Julian Huxley as the major questions in biology, and Tinbergen merely
added a fourth question, development. Tinbergen’s four questions are
sometimes collapsed into two categories; proximate or causal questions
(causation and development) and ultimate or functional questions (function
and evolution). These distinctions have often led to confusion and controversy
(see Hogan & Bolhuis, 2009). Bolhuis (2005, 2009) distinguished between
functional questions (function and evolution) on the one hand, and questions
about mechanism (causation and development) on the other. But no matter
how these questions are broken up it is crucially important that students of
animal behaviour be quite clear as to the type of question they are addressing
when they study or speak of animal behaviour. Tinbergen’s analysis is so
important that we would say that you cannot really understand animal
behaviour if you do not also understand the meaning of Tinbergen’s four
questions. Some of the more heated contemporary debates in the field of
animal behaviour can often be traced to misunderstandings about the meaning
of the four questions (e.g. Hogan, 1994; Bolhuis & Macphail, 2002). It is
essential, therefore, that any productive discussion about animal behaviour
involves participants that are capable of clearly stating which of the four
questions they are addressing.
Tinbergen’s four questions are sometimes also called the four whys,
because they represent four ways of asking ‘why does this animal behave in
this way?’ Let’s consider a bird singing at dawn, say a male song sparrow
(Melospiza melodia). The question is: why is this bird singing? This seems a
perfectly straightforward question, but in fact it is much more complicated,
because it can take any of four different forms. These different forms reflect
Tinbergen’s four whys. The first of the four questions concerns causation:
what causes the bird to sing? Another way of asking this is: what are the
mechanisms underlying the male’s singing behaviour? These mechanisms
involve the ‘machinery’ that operates within the animal and which is responsible
for the production of behavioural output. The topics include the stimuli or
triggers of behaviour whether they be internal or external, the way in which
behavioural output is guided, factors that stop behaviour and the like. These
are questions concerning the causation of behaviour. Sometimes this is called
motivation (e.g. Hogan, 2009). The question of the causation of behaviour is
the subject of the papers reproduced in Volume 1 of this book. The second
question is about development: how did the singing behaviour of the bird
come about in the lifetime of an animal? It turns out that a male song sparrow
does not sing immediately after it has hatched from the egg, but that it takes
quite some time before it has developed a song, a process that involves learning.
Such questions that concern development of behaviour, sometimes also called
ontogeny, are the subject of the papers reproduced in Volume 2 of this book.
The third question has to do with function: what is the function of the bird
singing; what is it singing for? This question has to do with the consequences
of singing for the singer’s fitness. Does singing help the bird keep intruding

males away from his nest? Or does it simply serve to attract females?