Have you ever asked yourself—Who shapes you? Who is responsible for your identity, personality, and intelligence? What makes you the you? Well, some of you might answer—We are the products of our genes and heredity, which we get from our parents and some of you might answer—We are the products of our environment, culture, and experiences. But, which answer is right? In reality, there is no clear answer. And, these questions are also not new, philosophers had been asking these questions for thousands of years; this debate is known as Nature versus Nurture.
In 1869, an English polymath Sir Francis Galton coined the term Nature vs Nurture. Here, Nature refers to the genes and hereditary traits—that we are born of—and Nurture refers to—our environment, culture, and experiences. And, the history is really old, filled with speculations.
However, in 1690, English philosopher John Locke proposed: human behavior is exclusively acquired from nurture. In his Essay Concerning Human Understanding, he used the word, “White Paper” in book II, Chap1,2. According to him, the brain is an information processing machine without any rules—like a white paper—in which interplay of experiences and environment etches it to form behavior and personality. This view is known as the blank slate view or blank slatism in modern-day psychology, which denies the effect of human nature. In fact, the concept of blank slate was first described in the writings of Aristotle as tabula rasa. It was then developed by stoics, Avicenna (11th century), Ibn Tufali (12th century), and Aquinas (13th century). Consequently, the credit for the modern idea goes to Locke.
Afterward, in the second half of the 20th century, clashes between both ideologies were at the peak. Researches demonstrating effects of both views on human development. The turning point was the stories of twins and research conducted on them. James Arthur Springer and James Edward Lewis both were identical twins, reunited together in February 1979, at the age of 39. After living the first 4 weeks together, they were reared apart. They both look identical—as all identical twins. Even being grown up in different environments, both were astoundingly similar. Both of them married and divorced women named Linda. The name of their second wife was Betty. Springer and Lewis both named their first son Alan and Allan, respectively, and many more things were similar.
The story of Springer and Lewis dumbfounded many scientists. Since, both are identical twins—developed from the same zygote[1]—share their 100 percent genes and are so similar not only in phenotype (their appearance) but also in psychological characteristics, and stories like this made the heads of the scientists itchy. As a result, research had been conducted, on many twins, to find an answer to nature versus nurture debate. As expected, the results were stunning, in the sect of nature. According to the new research, the heritability of IQ can be whoppingly up to 80%; Disorders like Schizophrenia, Bipolar disorder, and autism are also awfully heritable—up to 80%—as compared to diseases like breast cancer and Parkinson’s disease[2].
There are also opposites of the story of Springer and Lewis—twins having 100 percent same DNA but having different fates. And, one twin suffered from schizophrenia, but not the other one, despite having an intact copy of genomes[3]. How? During the 1950s, an English Embryologist Conard Waddington, tried to understand the phenomenon—How do environmental signals affect a cell’s genome? He was amazed by the development of all the cells of the body from a single embryonic cell. He stated this phenomenon of effects of the environment in modifying genes as, ‘Epigenetics’ (epi means upon or above) means above genetics.
Meanwhile, the testament of Waddington’s theory was provided by the dreadful event. Amid 1944 the dead-end of world war II German-occupied Netherlands underwent a fatal famine. After the liberation of the southern Netherlands from food shortage by allied forces, they were delayed in their advancement towards north and western sides due to being unsuccessful in seizing the bridge across the Rhine at Arnhem. And, in September the strike by the National Railways to further the liberation efforts by allied powers. As a result, the German administration banned food supply to the western part. Also, they demolished the docks and bridges to flood the country and inhibit the advancement of the allied army. Trains were stopped, Roads were choked, and water transport was frozen. The wartime ration reaching people dwindled to minuscule. Food stock falls apart. In the chilly winter, first butter disappeared, then meat, bread, and so on. Desperate, destitute people consumed tulip bulbs and sugar beets in their gardens. And, this period is known as the Hongerwinter or Hunger Winter in Dutch history.
Consequently, thousands of people died. Children who survived the famine also suffered from diseases caused by malnourishment: depression, osteoporosis, heart diseases, and many more. The engrossing thing was: the children, who were born by the women who suffered from winter hunger amid their pregnancy, had higher chances to suffer from obesity and heart diseases. And, the peculiar thing was the grandchildren of the sufferers of famine also had the higher chances to suffer from obesity and heart diseases. No one expected: the effect of famine will change the destiny of future generations. Due to calorie deficiency, the metabolism of sufferers changed and somehow transferred the cope-up mechanism—to store extra fat—from the calorie deficiency. There was something like memory transferred through genes.
But How can a gene store memory? Later, in the 1970s the scientists found marks on genes—a methyl tag—which changes the meaning of genes without any mutations. We can assume a gene ‘C’ and methyl tag was like a vertical bar ‘|’. And when the|’ get attached upon the ‘C’, it will not change the ‘C’ but changes its meaning to the character like reversed ‘D’.
Subsequently, in late 1996, a biochemist named David Allis found another intriguing factor that inscribes permanent marks on genes. These are histone proteins. Since, DNA is like a long string, and to fit it into the tiny nucleus, we need histone proteins. Histone proteins are globular proteins that wrap the DNA around itself tightly like—a thread wrapped around the ball—into the coils and loops. Genes are the functional units of DNA, which transcribes RNA. The interplay of RNA, ribosome and molecules of amino acids make proteins, and this process of protein making from RNA is called translation. The resultant proteins carry out functions in the cell. But, the transcription of RNA from a gene is only possible when the DNA is deconvoluted—not tightly packed around the histone proteins. Therefore, the convolution and deconvolution of DNA by histones turn on and off the genes—acting as a master switch. Ultimately, changing the physiology of the cell.
Throughout the winter, due to changes in the environment, the body of sufferers got a message—to increase survivability—communicated throughout cells by hormones. Eventually, the proteins in the cells modified genes adding or removing methyl tags and modifying the histones. This resulted in the altered genetic memory that passed to the children and grandchildren. In the same way, twins also have resulted in different fates, due to the change in the environment in which they grew up.
In conclusion, we are not merely the product of nature or nurture alone. The circumstances, experiences, and the environment—pre or postnatal—in which we grow up and live, with the interplay of genes, shapes us. It’s a combined force. And, the debate should end with the answer as epigenetics.
[1] The zygote is the first diploid (containing 2 pairs of every chromosome, a total of 23 pairs of chromosomes. And, chromosomes are the condensed form DNA) cell formed after conception (fusion of sperm and egg).
[2] Since personality, intelligence, and diseases like schizophrenia are such complex attributes, it’s unclear which genes they depend on.
[3] Set of haploid chromosomes, that is present in germ cells, having only 23 chromosomes.
By Yashovardhan Shakya
