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 including ourselves.

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.