Читать книгу The Behavior of Animals - Группа авторов - Страница 19

Niko Tinbergen published a very important paper in 1963, in which he outlined four major questions in the study of animal behavior, namely causation, development, survival value, and evolution. As he readily admitted, Tinbergen wasn’t original, because three of these questions (causation, survival value, and evolution) had already been put forward by the British biologist Julian Huxley (1887–1975) as the major questions in biology, but Tinbergen added a fourth question, development. Many authors, including ourselves, use the word function as a substitute word for survival value, but the term function is used in many different ways in biology (Wouters 2003), and care is necessary when using it. It should also be mentioned that the evolutionary biologist Ernst Mayr (1904–2005) in 1961 popularized a different categorization of problems in biology: proximate and ultimate causation. Proximate causation is similar to Tinbergen’s causal question, but ultimate causation is a controversial term that deals with evolutionary issues somewhat differently from Tinbergen’s questions of survival value and evolution. However, no matter how these questions are broken up, it is crucially important that students of animal behavior be quite clear about the type of question they are addressing when they study or speak of animal behavior.

We find Tinbergen’s analysis so important that we would say you cannot really understand animal behavior if you do not also understand the meaning of his four questions. Some of the more heated contemporary debates in the field of animal behavior can often be traced to misunderstandings about the meaning of these questions (e.g., Hogan 1994, 2017; Bolhuis & Macphail 2002). It is essential, therefore, that any productive discussion about animal behavior involves participants that are capable of clearly stating which of the four questions they are addressing. This view of animal behavior has also served as the framework for the organization of the present book, with the first half covering mostly causal and developmental topics while the second half deals with questions of survival value (or function) and evolution.

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 not, because answers can take any of four different forms. These different forms—you’ve guessed it—have to do with Tinbergen’s four questions. The first question concerns causation: what causes the bird to sing? The answers include the stimuli or triggers of behavior whether they be internal or external, the way in which behavioral output is guided, factors that stop behavior, and the like. These are questions concerning the causation of behavior. Sometimes this is called motivation, a topic discussed at length in Chapter 3. Tinbergen’s question of causation also concerns the mechanisms or structure of behavior. These mechanisms involve the “machinery” that operates within the animal and which are responsible for the production of behavioral output (Chapters 5 and 9).

The second question is about development: How did the singing behavior of the bird come about in the lifetime of an animal? A male song sparrow does not sing immediately after it has hatched from the egg, and it takes quite some time before it has developed a song, a process that involves learning. Such questions that concern development of behavior, sometimes also called ontogeny, will be discussed explicitly in Chapter 7. The third question has to do with the consequences of singing for the singer’s fitness: What is the function of the bird singing; what is it singing for? Does singing help the bird keep intruding males away from his nest? Or does it serve to attract females? Or does it do both? The topic of function (survival value), its methods of enquiry, and main findings will be discussed explicitly in Chapter 11. The fourth question concerns evolution: how did this behavior come about in the course of evolution? Behavior does not leave fossils behind and so the study of its evolutionary history requires the development of special methods. These methods, based on taxonomy and comparisons among species, will be discussed in detail in Chapter 15.

The previous paragraph illustrates that the question “why does this bird sing?” is not very useful, as it can have four different meanings. It can be very confusing if a biologist studying birdsong does not make it clear which of the four “why questions” he/she is asking, and it could lead to futile arguments concerning whether the bird is singing to attract mates or because it learned its song. The same problem arises in all other areas of animal behavior, so it is very important to make clear which question is being addressed in any study. Of course, it is possible that a particular investigator wants to address more than one question at a time. This is perfectly legitimate, as long as it is made explicit which of the questions are addressed at what time. A famous example of this is an experimental paper by Tinbergen and his associates (Tinbergen et al. 1962) on the behavior of blackheaded gulls (Larus ridibundus). After the chicks have hatched, the adult birds remove the empty eggshells from the nest. Tinbergen and his students investigated both the causation and the function (survival value) of this behavior using elegantly designed simple field experiments. They discovered the stimulus characteristics of items removed from the nest and, in the same paper, also reported results relevant to nest predation.

There is also considerable overlap among the four questions. For instance, the development of behavior is essentially a causal problem but may also involve functional aspects (Chapter 7). The evolution of behavior often depends on mechanism. For instance, emergent properties of an animal’s sensory and perceptual capabilities (mechanisms) may create opportunities for sexual selection to operate in the evolution of extravagant traits (Chapters 12 and 14). Finally, questions in one domain (e.g., function) can provide clues for questions in another domain (e.g., causation). For instance, a number of bird species cache food, some for a few hours, others for months (Vander Wall 1990). It is plausible that the ecological circumstances that have given rise to these different forms of food caching may have also influenced the birds’ ability to memorize spatial locations. In fact, a large number of studies are concerned with investigating the spatial memory of food caching versus nonfood-caching birds (Chapter 8).