We have all learnt the basics of genetics and Darwin’s theory of evolution in our schools. We learnt that evolution is a slow process and changes to a species in response to changing environmental conditions takes place over many generations( 100s possibly). We also learnt that sometimes there are random genetic mutations in our DNA- these are very small in number( less than 0.001% of our genes). Over many generations some individuals carrying these mutations becomes more suited for survival in the environment. That set of individuals survives and the others perish or their numbers decreases and slowly over many many generations the species evolves.
Today I will tell you about a remarkable new subject which changes all this. The interesting thing is that this new and amazing subject revives a very old theory of evolution.
In 1809 the French biologist Jean-Baptiste Lamarck proposed that an organism can acquire new characteristics during its life and these can be passed on its offspring. He proposed that if an organism uses a part more, that part grows in size or becomes strong and the increased size/strength can be passed on to its offspring. Similarly if an organism does not use a part, that part becomes smaller or weaker and that characteristic is passed on to its offspring. In the offspring also that particular part will be smaller or weaker. Lamarck used his theory to explain the long necks of giraffes.
Note that Lamarck proposed this theory much before Darwin’s theory of natural selection which was published in 1859. Darwin’s theory was completely different from Lamarck’s theory. Darwin’s theory tells us that if an individual adapts to his environment that adaptation is not carried forward to the subsequent generation. Later Mendel’s experiments gave the mechanism behind Darwin’s theory and that resulted in the modern theory of evolution and genetics. So according to this theory if an individual uses a part of his body more, that part may become stronger during the life of the individual but that strength is not carried forward to the subsequent generation. The subsequent generation just gets the father and mother’s genes without the information as to how their lives was lived. No information as to how the individual adapted to its environment is carried forward. Lamarck’s theory was nearly forgotten and Darwin-Mendel’s theories became modern genetics.
Scientists even gave this principle a name: Weismann barrier. So the Weismann barrier refers to the principle that information flows from the genes to the rest of the body and never is reverse. To be more precise, information only flows from germline cells(genes) to the somatic cells(other cells). So modern generics believe that the Weismann barrier cannot be penetrated. So what we experience using our sensory organs cannot affect the genes because it cannot penetrate the imaginary Weismann barrier.
In the last few years scientists have analyzed new data which could not be explained by modern genetics. A group of scientists studied the population of a region in northern Sweden over several generations. This region had many years of famine in the 19th century. And there were several years of abundant harvest and food. The scientists studied life expectancy of many generations and tried to associate it with the famine and food abundant years. They found that the children of people who had gone through even one year of famine had a different life expectancy from children of people who had never seen a famine. Children of people who enjoyed over abundant food lived less longer than children of people who had seen famines. So the adaptation to food scarcity had carried on to future generations! The amazing thing is that even if a person had seen a famine year in his childhood, his child will have an increased lifespan. The complete data is too large to write here but the important point is that what we experience in our lives does get carried over to our children.
Where is this information carried? In our genes? NO! Our genes remain the same whether we smoke or not. Our genes do not change depending on whether we do intellectual work or not. Our genes do not change if we starve. This information is carried in how the genes express themselves. So the same genes may express themselves differently in different people. Thus this subject is named epigenetics- beyond genetics.
Over time evidence for more epigenetic factors were found. One experiment showed that if an individual smoked his children are more prone to obesity and shorter life spans. We are not talking about a mother smoking during pregnancy. We are talking about smoking much earlier in life. And this happens even if the father smoked much earlier in life- even before adolescence-even before the first sperm cells were formed. So the observation was that smoking causes a change in the gene expression though it does not change the genetic makeup of the individual. And this gene expression can be carried on to future generations. How many generations? Not forever like the genes. But it can be carried over up to 15 generations.
How does this work. One of the most common mechanisms is DNA methylation. When a methyl group attaches itself to a gene, it can change the gene expression. It can make it “louder” or even “silent”. The gene may be the same but what you do in your life may change how it is expressed. And this expression is carried forward. Another Epigenetic technique is known as genomic/genetic imprinting. We have already read about it in an earlier VERITAS when we found out why Ligers are much larger than Lions and Tigers while Tiglions are much smaller than both. ( See VERITAS: Liger, Tiglon and Genomic Imprinting Jan 14, 2010. Available at http://unvarnished-veritas.posterous.com/liger-tiglon-and-genomic-imprinting)
Epigenetics is a very exciting new area of research. It gives us a good news and a bad news. First the bad news. Don’t just blame it on the genes. We are passing on not just the genes but also how they will be expressed to our children. We may not have control over the genes but we do have some control over the epigenetic factors. Now the good news: These new discoveries are opening up new areas of research- How can we make drugs that turn down the expression of certain harmful genes. Maybe epigenetics will bring us the next generation of cancer or Alzheimer drugs.
So it turns out that though Darwin was not wrong but Lamarck was also right. Darwin was telling us about how genetic evolution takes place. And Lamarck was telling us how our lifestyles change the epigenetic factors and that they can be inherited.
It is such a beautiful and interesting world out there. The only tragedy- life is short!
Go wondrous creature, mount where science guides
go measure earth, weigh air, state the tides,
instruct the planets in what orbs to run
correct old time, regulate the sun