Studying the molecular evidence for the inheritance of animal behaviour involves understanding how genotypes affect phenotypic traits.
A phenotype consists of all the observable properties and characteristics of an individual (gg). This includes behavioural characteristics such as intelligence (gg). The genotype which influences the phenotypes is made up an individual’s entire complement of DNA (gg). An individual’s environment along with its genotype affects the phenotype displayed (gg). For example, a behavioural phenotype such as aggression towards other species may not be displayed if the competing species are not present. Inheritance of a genotype comes from both parents.
It is commonly thought that all traits (phenotypes) are inherited through single genes (f). Of course for some phenotypes such as flower colour in peas this is the case; the colour is affected by two genes inherited from the parental generation (white recessive and purple dominant) (Campbell and Reece). Traits which are connected to behaviour in animals are generally not inherited through single genes; behaviour mostly stems from a more complex genetic basis (f). An example of a single gene influencing behaviour is the MAOA gene; studies have indicated that genetic deficiencies in MAOA activity have directly affected aggression levels in mice and humans (K). Behavioural conditions such as this one are rare and most behaviour is not inherited this simply (F). Multiply genes are usually involved and it is their effects combined with environmental factors that influence behaviour in animals (F). An individual’s behavioural differences are affected by DNA variations; as all animals including humans have unique genotypes, every animal’s behaviour will vary (f). This does not mean every animal will differ completely; animals are born with instinctive behaviours that all animals share such as visual perception (B). Animals within a species share inherited behaviour patterns (b). For example some species of the Cuckoo bird are broad parasites; they lay their eggs in the nests of other breeds of birds. When the Cuckoo chicks are born they have been known to eject the other eggs or young of the host bird; since the Cuckoo chick has never been in contact with its parents this instinctive behaviour must be genetically determined (beta cuckoo). Instinctive behaviour within a species such as the Cuckoo bird proves that some behaviour is genetically determined and is not learned.
Many traits are not viewed as being “present” or “absent” but rather they are displayed to a greater or lesser extent (gg). In animals there is variability between behavioural characteristics of individuals, this is called population variation (gg). When the frequency of the effect is plotted against the magnitude, many of these continuously distributed characteristics show a bell-curve distribution that is known as a normal distribution (gg). Most individuals within a population will lie somewhere in the middle of the population distribution, but some individuals will lie on the ‘tail’ regions of the population distribution (gg). In relation to behavioural traits, lying on the ‘tail’ region could mean behavioural problems (gg)
The normal distribution graph (bell-curve) shows individuals of a species or ‘group’ do not always have the same behaviours (gg). The genotype of an individual will determine the behaviours it will display; therefore animal behaviour between species will be similar but not exactly the same.
The study of behavioural genetics
Behavioral genetics is the study of the role that genetics play in animal behaviour, in conjunction with environmental factors and heritability. Via the development of hormonal and nervous mechanisms, the external environment has a large influence on how genes are expressed in behaviour.
Behavioral geneticists aim to discover the determinants behind behaviors, which is also associated with the ‘nature vs. nurture’ idea (Encyclopedia). Because behavioral genetics involves contributions from genetics, biology, statistics, ethology and psychology, it is said to be highly interdisciplinary (Encyclopedia).
The most commonly used methods of researching behavioral genetics in animals are breeding, transgenesis, or gene knockout techniques (Fuller & Thompson), and in humans the twin or adoption studies are used (Fuller et al).
The following are indications that behaviors have a biological base: (Joseph McInerney). Behavior is often species specific, behaviors often breed true, behaviors can change in response to alterations in biological structures and processes and behavior has an evolutionary history that continues across closely related species (Joseph McInerney).
Nature vs. nurture: how each contributes to behaviour in animals
A combination of genetic and environmental factors are influential on the psychological traits expressed by all living things (D’Onofrio, 2008). Gene-environment interactions or relationships are studied simultaneously to determine whether traits expressed are more dependent on genetics (nature) or the environment (nurture) (Balasubramanian, 2008 & D’Onofrio, 2008). While scientists acknowledge that both genes and the environment are influential on species development and behaviour (Balasubramanian, 2008), species genes for behavioural traits and the environment which modify them are now being examined (Balasubramanian, 2008).
Darwin said our behaviour (and that of animals) is the result of not learning, but biologically inherited traits. 120 years following his death, scientific evidence proved him right (Baschetti, 2008). New data from heritability studies are capable ofrevealing the influence of genotype relative to genotype relative to the environment (Bors, 1994). As Johnson (1990) implied, the old “nature versus nurture debate” was built on assumptions of genetics and behaviour that we question now in light of new understandings of the matter.
“Nature versus nurture” or “genes versus environment” are narrow minded notions that are poorly understood (Dess, 2001). Rhesus monkeys share 94% of their genes with humans, deeming them very helpful in behavioural and genetic studies (Dess, 2001). Distinct personalities develop in these species which appear early in like and typically remain stable inti adulthood. Experiences early in the life of individuals have proven substantially influential in altering certain tendencies and predispositions. This alone suggests a genetic influence on the behaviour of the species (Dess, 2001). Similarly designed studies in maternal rodent behaviour by Canadian Neuroscientists for example are providing similar suggestive results that behaviours including breastfeeding and grooming are actually passed down genetically (Couzin, 1999). Such behaviours are seemingly programmed by the individuals genotype (Couzin, 1999). Studies of gene-environment interactions are allowing the opportunity to treat genetic disorders (Wahlsten, 1994). In human studies for example genetic research is enabling us to identify what genes are involved with which disorders, how they work and what help can be provided (Wahlsten, 1994). These improvements in understanding with our advances in research mean genetic analysis of behavioural traits is beginning to demonmstrate the greater influence of molecular evidence on behavioural traits and tendencies in the hierarchy of influences (Gottlieb et al., 1991).
In our attempt to decide the relative importance o genotype and environment for a given phenotype, genetic factors are proving more important than previously thought (Bors, 1994). However in all species, we do maintain that development and phenotypic variation is the result of and can be accounted for by:
An interaction between genotype and environment
Environmental factors alone
Or by a combination of these.
It is because of the diversity of our environments that no single developmental/behavioural outcome is going to be optimal in all conditions, and “bad genes” do persist (Dess, 2001). Genes programming “bad” behavioural outcomes many be expressed positively under ideal circumstances.
Animal behaviour, like human behaviour, is the result of developmental, genetic, evolutionary and cultural aspects (de Waal, 1999). Abilities, diabilities, temperament, behavioural syndromes and disorders are such examples of these interactions between genes and the environment (Balasubramanian, 2008). The cultural dogma that “human behaviours reflect nurture, represented by social environments, not nature, in the form of biological factors,” is far from being resolved but gradually becoming more accurately understood (Baschetti, 2008 & Bors, 1994). Mounting evidence that points to a heavier genetic influence on many behaviours than most psychologists were previously prepared to acknowledge” (Johnson, 1990).
Nature vs. Nurture: Case studies
It is believed that animal behaviour is not entirely determined by genetic traits but from a combination of environmental, learnt and heredity influences (Bolhuis & Hogan 1999). Behaviour may begin as an innate behaviour at a genetic level but through environmental and social influences the behaviour can be morphed and developed well beyond the initial expression (Bolhuis & Hogan 1999).
A study was taken undertaken by A.L Reid, F, Seebacher and A.J.W Ward on the predatory fish the jade perch (Scortum barcoo), shows just how this genetic trait can be morphed by environmental and social pressures. To begin the study juvenile fish were separated into three different groups with each group undergoing separate treatments regarding prey. One group was given experience with live prey, another with freshly killed pray and the last group were given pellets. They then tested the response of the predators to live prey (Reid, Seebacher & Ward 2010). There was no difference in the number of attacks made by the predators however there was a significant difference between the numbers of predators who successfully captured their prey (Reid, Seebacher & Ward 2010). The jade perch group that had not had previous exposure to feeding on live prey were more successful than those who did not. The results suggest that the recognition of prey is a hereditary behaviour however the hunting skill is further developed by learning and the environment.
An earlier study undertaken by H.J Eysenck and D.B Prell in 1951 looked that at the inheritance of neuroticism traits in children and to what percentage this inheritance was either due to environment or hereditary factors. All the children were of the same age and included fraternal and identical twins. A factorial analysis called ‘criterion analysis’ was undertaken on the results of the personality tests (Eysenck & Prell 1951). The results showed that eighty percent of individual difference in neuroticism traits was due to heredity and only twenty percent were from environment (Eysenck & Prell 1951).
Mapping of phenotypes onto gene or protein arrays have made it possible to further analyse complex genetic behaviours (Barbosa & Castellanos 2005). Barbosa and Castellanos performed a high density gene mapping technique on Caenorhabditis elegans a bacteria feeding nematode. During their study they found that there was a single nucleotide difference in a gene that is associated with sensitivity to touch (Barbosa & Castellanos 2005). This one small difference can account for a difference in foraging behaviour found in natural populations (Barbosa & Castellanos 2005). It was previously thought the differences in feeding habits were due to different environmental conditions.
The results from these three different studies all show evidence of animal behaviour being linked with heredity genes but also a combination of both environment and learnt behaviours. Certain animal behaviours start of as a genetic response but are then further developed through environment and social interactions.