Biology Reference
In-Depth Information
(how behaviour evolves by natural selection). But first, we need to be
clear about exactly what we mean when we ask the question 'why?'
Tinbergen's four 'why' questions
Niko Tinbergen (1963), one of the founders of scientific studies of animal
behaviour in the wild, emphasized that there are four different ways of
answering 'why' questions about behaviour. For example, if we asked why
male starlings sing in the spring, we could answer as follows:
(1)
In terms of
causation
. Starlings sing because the increasing length of
day triggers changes in their hormones, or because of the way air
flows through the vocal apparatus and sets up membrane vibrations.
These are answers about the mechanisms that cause starlings to sing,
including sensory and nervous systems, hormonal mechanisms and
skeletal-muscular control.
(2)
In terms of
development or ontogeny
. For example, starlings sing because
they have learned the songs from their parents and neighbours, and
have a genetic disposition to learn the song of their own species. This
answer is concerned with genetic and developmental mechanisms.
(3)
In terms of
adaptive advantage or function
. Starlings sing to attract mates for breeding,
and so singing increases the reproductive success of males.
(4)
In terms of
evolutionary history or phylogeny
. This answer would be about how song
had evolved in starlings from their avian ancestors. The most primitive living birds
make very simple sounds, so it is reasonable to assume that the complex songs of
starlings and other song birds have evolved from simpler ancestral calls.
Fig. 1.1
A foraging starling.
Photo © iStockphoto.com/
Dmitry Maslov
Proximate versus
ultimate
explanations
Causal and developmental factors are referred to as
proximate
because they explain
how a given individual comes to behave in a particular way during its lifetime. Factors
influencing adaptive advantage and evolution are called
ultimate
because they explain
why and how the individual has evolved the behaviour. To make the distinction clearer,
an example is discussed in detail.
Reproductive behaviour in lions
In the Serengeti National Park, Tanzania, lions (
Panthera leo
) live in prides consisting of
between three and twelve adult females, from one to six adult males and several cubs
(Fig. 1.2a). The group defends a territory in which it hunts for prey, especially gazelle
and zebra. Within a pride all the females are related; they are sisters, mothers and
daughters, cousins and so on. All were born and reared in the pride and all stay there to
breed. Females reproduce from the age of four to eighteen years and so enjoy a long
reproductive life.
For the males, life is very different. When they are three years old, young related males
(sometimes brothers) leave their natal pride. After a couple of years as nomads they
attempt to take over another pride from old and weak males. After a successful takeover
