Decoding human behaviour – Part 3 – Is Epigenetics a new invention? Some common examplesSeptember 11, 2020 7:31 pm
Is Epigenetics a new invention? Did it exist before we heard about it?
Epigenetics is not new. It existed with life on earth. Scientists have done the christening ceremony after they found its molecular mechanism. The concept originated about fifty years before Charles Darwin published his famous book On the Origin of Species in November 1859, when the French naturalist Jean-Baptiste Lamarck proposed that surrounding conditions can modify characteristics acquired during a person’s life time and those characteristics can be passed on the offspring. What he meant could not have been anything other than Epigenetics. The credit for coining the term went to Conrad Waddington (1905 – 1975) known for Waddington’s Epigenetic Landscape which no student of this field can afford to miss.
Let us familiarise epigenetics with help of a few common examples of the environment controlling the genetic function and how life is redesigned by the environment we live in.
We, humans, are the best example of the lot. We are a set of different people in appearance, behaviour, health and disease proneness though we possess the same genetic structure.
Human body is made of trillions of cells that make complex organs and tissues. Every cell in our body is derived from the same starter cell, the zygote formed when sperm and egg fuse together. As the zygote divides, cells become differentiated into organs to carry out specific functions. For example Liver cells function only as liver cells, It cannot do what kidneys or brain or eyes do. Liver produces only liver cells, muscles only muscle cells and so on. How?
During differentiation to organs, the cells undergo either irreversible loss or inactivation of the genetic materials not required in a particular tissue. Or else we would be left with our liver producing kidneys, skin producing eye balls or eye balls sprouting teeth giving a monstrous look for humans. We should be thankful to the creator. This irreversible inactivation of gene is probably the most crucial instance of epigenetics in human development.
The infamous Dutch Hunger Winter, which lasted for about six months in Europe till the spring of 1945 following the Second World War revealed certain interesting insights into the role of environment on the functioning of genes. Starvation was so intense in Netherlands that people often lived by eating grass and tulip bulbs. Epidemiologists found that mothers who were malnourished during the last three months of pregnancy had small babies, as foetuses do most of the growing in the last few months. Surprisingly, these small babies continued to stay small all through their lives though they had access to sufficient food.
On the other hand babies whose mothers were malnourished only during the first three months of pregnancy were of normal birth weight. But had high obesity rates apart from many other health problems though these children appeared healthy at birth.
Something that had happened while they were in different stages of pregnancy had affected their lives for decades. Some of these traits were inherited by the subsequent generation too. It leaves a puzzling question. How?
Identical twins, easily the best example of two individuals sharing the same genetic code, should be alike not only in appearance but in health and disease. On growing up they exhibit behavioural characteristics and disease proneness different from each other. For example if one of the twins has schizophrenia or bipolar disorder the chances of the other twin developing similar illness is definitely higher than in general population but often not 100%. Why?
In a study report as recent as June 2020 authors Helen Fisher and Aaron Reuben have highlighted that even a child’s neighborhood impacts their health for years to come.
Adverse Childhood Experiences (ACE) in the form of poor parental care, traumatic events , abuse or neglect play significant role in causing mental health issues later in their life though as an adult they may not have any recollection of the traumatic events. Why? Are they causing any indelible changes on gene expression?
We believe that foetus in the womb is in a protected environment and immune to changes happening outside. It is factually incorrect as foetuses are known to be affected by what is happening in the surroundings. There are a couple of well- known examples of the impact of environment on unborn child which affected them later in their life (nutrition apart).
The famous story of Abhimanyu in the ancient Indian epic Mahabharata (who could not find the way out from Chakravyuha when it was required) is a typical example. But why does it happen and how?
About three or four decades ago there was a report by Russian scientists who claimed to have made super kids by subjecting pregnant mothers to sound waves of a particular frequency, and interestingly they had quoted Abhimanyu story in support of their research finding.
‘The X-Chromosome Tragedy’
We know that chromosomes are the carriers of DNA and that there are sex chromosomes. Males have only one X chromosome while females have two X chromosomes, a disparity to be certainly addressed to. X-chromosome carries about 1300 genes in it. That means the females will have double the number of genes. As we have come to know by now, genes are destined to synthesise proteins, the building blocks of the body. If all the 2600 genes from two X- chromosomes make proteins, there will be utter chaos in the cytoplasm of the cells, a hazardous situation will ensue and life itself may be jeopardized. We often say ‘God is Great’. It is true. One X- chromosome in the female gets inactivated right in the embryonic stage (X- Inactivation) and solves all the confusion. This is epigenetics par excellence.
Experimental evidence: Well- groomed rats are happy rats.
Laboratory experiments using rats showed that the amount of licking and grooming (maternal care in animals) received during infancy had direct effect on how stress hormone genes were expressed. The more licking received as babies, the lower the stress as grownups. Pups, who had inattentive mother who scarcely did licking and grooming, grew up as nervous wrecks, unable to cope with stress in later life.
Stress hormone genes apart, inattentive mothering in rodents suppress the genes for oestrogen receptors in brain. And when these babies grew up the resulting decrease of oestrogen receptors made them less sensitive/ attentive to their babies.
Could it be a reason behind ‘Mothers who kill their children’?
In humans, music may be considered as equivalent of Licking and Grooming in animal models. Music is a universal component of mother – child relationship. It has been demonstrated that mother’s voice (not irrelevant, of course) can protect the child from dysregulation of certain important brain receptors (Dopamine, Serotonin and Glutamate) by epigenetic mechanisms.
‘Live life Queen size’– Honey bee colony has a Queen and plenty of worker bees. Though genetically identical, queen bee is double the size of worker bee. Has life span twenty times higher than other members of the colony and is entitled to enjoy special privileges. She lives on royal jelly, is lucky to mate with a selected few males and has unique ability to lay eggs. How different from her companions!
It is believed that the pattern of early feeding determines whether the larvae will develop into a worker or a queen. Until the third day all larvae are fed royal jelly, thereafter only a select few are fed royal jelly and they grow up to be queens. Researchers attribute this to an epigenetic process royal jelly is capable of doing.
Interestingly enough, all these stories are basically linked at a biological level. All are examples of the new revelation in biology, Epigenetics.
It is worth remembering that health and longevity can be affected by the ways our parents and grandparents ate. The old adage goes like this:
‘You are what you eat
You are what your mother ate
You are what your grandmother ate’