Many sociologists wonder from where the increasing trait of violence man has acquired during thousands of years of his existence has originated. Mind boggling violence being witnessed amongst human beings is some thing having no parallel in this Universe and the expression "inhuman" or "humane" has no meaning because animals rank much lower in the scale of violence than man. Look at the most recent mindless slaughter of hundreds of people in Nigeria on religious grounds or almost daily suicide bombers causing havoc in Iraq, Pakistan and Afghanistan or the senseless killings by Maoists in India or the terrorists related loss of lives all over the world and the streak of cruelty is there amongst human beings. History is also replete with instances of mass murder for the sake of wealth, land or religion. How can one explain the cruelty often noticed amongst young children who do not have any sense of pity or kindness towards other smaller and harmless creatures? There are three distinct possibilities that can be relevant when the "cruelty" trait in humans are considered which include genetic make up, the environment that shapes one's life and the diet one consumes regularly.
Taking the connection between cruelty and genes, this is an area which has been researched for long without any consensus emerging amongst scientists. There are many theories based on limited studies and none of them can explain clearly this phenomenon. More recent studies are focusing on the gene that is responsible for expressing the crucial enzyme Monoamine Oxidase or MOA located in X chromosome in the humans which has the critical responsibility in deactivating excess levels of neurotransmitters like Serotonin, Melatonin, Norepinephrine and Epinephrine through oxidation into aldehydes and ammonia. The enzyme exists in two forms MOA-A and MOA-B, located in the outer membrane of cytochrome, found in neurons and astroglia. MOA-A has more specific role in dealing with the neurotransmitter amines. Lower as well as higher than than normal levels of neurotransmitters can cause depression, schizophrenia, substance abuse, attention deficiency disorder, migraine etc and MOA Inhibition therapy through drugs is practiced in severe cases. But the critical question is whether this gene which must have been present in ancient man is preserved without mutation during evolution and the traits of violence, brutality, aggression, cruelty etc are more evident in people with this particular gene gone berserk due to reasons not yet clear.
Coming to the environment, the most important question is whether the behavioral pattern in humans can be changed by continuous exposure to hostility or through deliberate training in hostile behavior as is being attempted by many violent and terrorist groups. Stray studies do point out to the tendency of children brought up in a hostile environment becoming cruel adults with least sensitivity to sufferings to others. While hostile or retaliatory aggression can be attributed to low IQ, planned or predatory aggression cannot be explained away so easily. Organized butchering of billions of living creatures for supplying food to the population to day probably can make consumers of the foods from these sources some what insensitive to killing which after all is a product of aggression and cruelty. Using terminology like Prevention of "Cruelty" to Animals, People for Animal, Beauty Without Cruelty cannot hide the fact that these killings take away the life of hapless creatures for humans to live. It is for the human psychologists to answer whether one who kills an animal as big as a beef cattle will have any feelings about extinguishing any other form of life.
Food appears to be least connected with violence or aggression. The astronomical quantity of animal derived foods being consumed to day are providing more nutrition to people, almost like the pre-historic man who had to be aggressive for survival. Though there are not many peer reviewed publications on any link between food and aggressiveness, a few stray reports do indicate that some foods can make animals like dogs more aggressive while others make them docile. In one of the rare studies with prison inmates, it was found that providing nutrient supplements along with regular foods made them less violent, more rule abiding and cooperative. Blood sugar variations are also under the scanner as consumption of high sugar foods like confectionery amongst school going children have been found to be responsible for their aggressive behavior later in life. Thousands of additives that go into processed foods have also been blamed by some for the change in behavior of children noticed lately.
Mahatma Gandhi, the great apostle of peace and violence, probably believed that human beings can train themselves to be "humane" without recourse to cruelty or brutality and his ability to harness an entire nation for peaceful agitation to shake of the colonial yoke is a classical testimony to his conviction which stands vindicated.