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Saturday Feature
 
Long hand of the gene
Syed Fattahul Alim
10/1/2005
 

          Do genes have any influence on the way people behave in social circumstances? Everyone knows that the genes dictate the formations of the various organs of the body. But social behaviours? Is that not going too far about the functions of the genes? The common understanding about the social behaviour of animals including, of course, humans is that it is mostly a learned behaviour acquired from the ecology comprising the community of the animal in question and the environment. After the birth of an animal, the teachers are at first the parents, then the fellow creatures as well as the natural environment. But this notion is now being shaken by new discoveries in the science of genetics. There are certain genes that dictate their choice of mating partners or even their occupational roles in the community. The researches are still limited to lower animals such as prairie voles, mice, fruit flies and the like. Conducting such research on humans is still a far cry, if only because of ethical reasons. But still the results of the researches, though conducted on inferior animals, have their implications for humans, too. However, direct extrapolation of these results to human subjects may suffer from the limitation of oversimplification.
Recent studies have revealed that certain genes, called fruitless genes or just fru genes, control the behaviour of fruit flies, for example, the male Drosophila fruit flies, as to how they will select their mating partners or how they will choreograph the complex pattern of courtship with their female counterparts. Scientist called these behavioural genes and have found some 30 distinct genes that are responsible for certain behavioural patterns of roundworms, mice, flies, voles and the like.
Scientists have long been aware of a gene that promotes faithful bonding of a male prairie vole towards the female member of the pair or its role as a good parent. The gene is naturally modulated among a population of voles to create a set of behaviours. Depending on the changes in the demographic ecology, the genes will dictate as to whether the animal will remain loyal to one wife or flirt with many others at the same time.
How the genes possibly control the behaviour of the subject animals? Some environmental signals switch on a neural circuit in the brain of the animals that dictate its response mechanism with other members of the population. Catherine Dulac of Harvard University, USA identified such signal carriers in the form of an airborne hormone, called pheromone, in the male mouse. Further, she identified a scent-detecting organ in the nose of the animal, the vomeronasal organ that can detect the pheromones. But if the scent-detecting capacity of this organ is impaired or blocked by some artificial means such as genetic engineering, the animal loses its capacity for responding properly to the environmental cue. Such a condition affects the animal's ability to distinguish between males and females. As a result, the male mouse so incapacitated may try to woo, rather than attack, another male mouse approaching it. Curiously enough, in the case of sexual behaviour of these animals, they do not use their eyes or ears to tell a male from a female. Rather they go through the complicated neural response aroused through the media of the vomeronasal organ. But in the case of the mouse, the behaviour-controlling gene that was removed from its overall genetic system that controls its mating behaviour was a low level member of the system. In the case of the Drosophila fruit fly the behavioural gene spotted was a rather high level one. When this gene called the fru gene was disabled in the male fly, it lost its interest about its female counterpart. On the other hand, as a strange twist of fate, the male fly then begins to evince a fascination for other male flies. Scientists have found that the gene responsible for this particular behaviour is arranged in blocks. A region of DNA acts as the promoter for the fru gene to produce different types of proteins by making various combination of gene blocks. In the case of fru gene, some four such promoters have been discovered. Three of the promoters function in a similar fashion in both the male and female flies. But the fourth one is the most crucial one, which dictates production of different proteins in the male and female flies. The special behaviour of the male fly to to attract the female before the mating takes place is largely due to this fourth promoter, the high level gene working as the master key. This gene is truly a behavioural gene that promotes the exclusive sexual behaviour of the male towards the female regarding mating. When scientists genetically programmed the male flies to produce female version of the protein and the female ones to make the male version of the same protein, a strange development in the characteristic of the flies occurred. The male flies so engineered genetically hardly showed any interest in the females. The female flies with the male form of the fru protein showed an intense homosexual propensity as they pursued other female flies aggressively. Barry J. Dickson of the Austrian Academy of Sciences carried out this interesting experiment recently. Dickson and his team showed that the protein is generated in the 21 clusters of neurons in the brain of the fly. The circuitry of the neurons has something to do with the triggering mechanism that controls the male fly's complex behaviour during courtship with the female flies. The scientists are yet to home in on the exact mechanism of this process. Oddly enough, the female flies do also possess this particular neuronal circuit. But for some strange reasons still unknown to the scientists, it is the presence of the male fruitless that trigger the circuit to create the particular pattern of male behaviour demonstrated during courtship. The fruitless, therefore, serves as the master switch gene to the activate network comprising other lower level behavioural genes in the system.
Similarly, honeybees either work as nurses in the hive or as foragers to collect honey. Which role the bee should play is also a function of the behavioural gene, and the signal regarding if they have to change their occupational roles is transmitted through pheromones.
Gene Robinson, a bee biologist at the University of Illinois, has coined the term sociogenomics as a branch of study the to understand social life of animals in terms of genes and signaling molecules that trigger them. The 30 genes discovered, which are believed to be responsible for certain social behaviours of the animals, have not found to be following any general rule define them.
He said that, "It's early days and we don't have enough information to develop theories."
Larry J. Young of Emory University, who studies the social behaviour of voles, said:
"In people, activities like the suckling of babies, maternal behaviuour and sexual drives are likely to be shaped by genes, but that sexual drives are also modulated by experience.
"The genes provide us the background of our general drives, and variations in these genes may explain various personality traits in humans, but ultimately our behaviour is very much influenced by environmental factors," he added.
About repeating the experiments, as done on the inferiors animals, on humans to vindicate those Catherine Dulac of Harvard University said,
"The problem with humans is that it is extremely difficult to prove anything...Humans are just not a very good experimental system."

 

 
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