The behaviour that is observed in both vertebrates and invertebrates
is something that is far too complex to be simply determined by genes.
The concept of Epigenesis can be used to explain more accurately the
patterns of behaviour observed in many animals including ourselves ......
Charles Darwin noticed that animals share many of the emotions and
feelings that are seen in humans. Does this necessarily mean that
these emotions are inherited? An alternative explanation is possible.
Another evolutionist, Lamarck, stated that two independent species
could, given a particular environment, develop the same physical and
mental characteristics. In this case the similarity of the features
could not be explained through some common evolutionary origin. One
sees a classic example of such 'evolutionary convergence' in dolphins
and certain fish. While some fish share a number of physical
characteristics with dolphins, the similarity can only be explained by
the fact that both fish and dolphins live in an aquatic environment.
Thus a potential problem arises for the naturalist- how is it possible
to distinguish between characteristics in different species that have
resulted from convergent evolution, that is from environmental
conditioning, and those characteristics that have arisen from a common
ancestral origin between two different species? Evolutionists must
examine all available evidence in order to determine whether a given
characteristic found in two animal species, is truely an indication of
common ancestral origins.
Animal behaviour - purely genetic?
Almost fifty years after Darwin, Konrad Lorenz and other evolutionists
were to proclaim an 'All Genetic' explanation for similar behaviours
between two independent species. According to Lorenz behaviour was
transmitted from a common ancestor to daughter species. Later Lorenz
was to admit that he had over estimated the role of genetic
inheritance in determining animal behaviour. Acquired learning was
clearly also an important component of behavioural patterns present in
animal species particularly within the warm blooded vertebrates.
Lorenz was thus able to create a genetic/learning scale of behaviour
ranging from invertebrates with virtually no learning component in
their behaviour to vertebrates with a big learning component in their
behaviour (eg: humans).
Is it really possible to discuss genes as behavioural genes?
According to Andre Langaney, scientists often make a fundamental
mistake when assessing the role that genes play in determining animal
behaviour. It is incorrect to say that because a mutation in a gene
causes a change in behaviour that the gene in question is necessarily
a behaviour-determining gene. Langaney uses the analogy that it is
not a transistor in a television that is directly responsible for
generating an image. However, if the transistor is not present, an
image will not be generated by the television. Of course the
transistor has a role to play in generating the television image but
it is just one of an ensemble of components that is necessary to
produce the image. In essence what Langaney is saying is that the
behaviour that is observed in both vertebrates and invertebrates is
something that is far too complex to be simply determined by genes
alone. The concept of Epigenesis can be used to explain more
accurately the patterns of behaviour observed in many animals
Epigenesis refers to a construction process within an organism that
supplements the information provided by the genetic make up of that
organism. Thus the development of human behaviour is dependent not
only on several genes but also on the interactions that occur between
the developing foetus and the mother followed by the social
surroundings in which the child grows up.
What is a truely genetically-inherited characteristic?
In humans great care must be taken when stating that a particular
characteristic is genetically inherited. A truely genetically
inherited characteristic or phenotype is one where conclusive evidence
has been provided to clearly support the finding that a given gene is
responsible for that given phenotype. A statistically-acquired
characteristic is one that can be predicted to be present in an
individual based on the presence of that characteristic in the
individual's parents. A talent for music in the parents, for example,
might give rise to a similar musical talent in the offspring. It would
be very wrong to assume that the talent for music in the offspring is
necessarily genetically inherited from the parents.
Case Study - an error of judgement: the crime chromosome is identified
In 1965, Patricia Jacobs and coworkers were to publish an article in
Nature revealing that 4% of inmates in a scottish prison carried two
copies of the Y chromosome rather than one. Within the general
population, the double Y chromosome has an incidence of about 1 in
1000. However, newspapers were to seize this article as clear
evidence that the 'crime chromosome' had been found (since the
incidence of the double Y chromosome was higher in inmates than within
the general population). An alternative explanation for the higher
incidence of the double Y chromosome in the criminal population was
provided. Since the double Y chromosome leads in many cases to mental
retardation in affected individuals, it is possible to imagine that
criminals carrying the two Y chromosomes might be more susceptible to
being caught in the act of commiting a crime. This would lead to a
rise in incidence of the double Y chromosome within the inmate
population of british prisons. However it would be wrong to conclude
that an additional copy of the Y chromosome in men naturally
predisposes them to crime.
The above example shows that extreme caution must be taken when making
conclusions about the role that specific genes play in determining
specific behavioural traits both in humans and in other animals.
Genes are only one component of a very complex set of factors that
determine behavioural traits. As already illustrated, epigenetic
factors that occur during both foetal and post natal development are
also extremely important. With the ever increasing knowledge of the
function of genes, it is essential to consider these epigenetic
factors if we are to fully understand both human and animal behaviour.