Chris Faulk is a postdoctoral fellow studying environmental epigenetics and evolution at the University of Michigan, School of Public Health. This is the first in a series of posts discussing the science of epigenetics.
Not all heritability is genetic, and humans, like all animals, have the ability to adapt to the environment.
One of the main mechanisms for altering gene expression is through epigenetics, literally “above the genome”. Epigenetics has been in the news lately for its potential impacts on human health, and has even been touted as requiring a complete overhaul of the modern synthesis of evolutionary theory. The basic premise of epigenetics is that chemical marks (DNA methylation, histone modifications, and bound non-coding RNAs) can result in gene expression changes and be passed down through cell division without changes in a cell’s DNA. If these changes are passed down through the generations, they are considered non-Mendelian, since they do not follow the law of genetic segregation. Practically, epigenetics means that the environment can impact your physical characteristics, your phenotype, and potentially even be passed on to your offspring. In this first post I will be discussing some historically mistaken ideas about non-Mendelian inheritance. In later posts I will review some of the current ideas in modern epigenetics and how they impact our view of inherited traits.
You may recall the ideas of Jean-Baptiste Lamarck who, beginning in the early 1800′s, put forth the hypothesis that giraffes could pass on long necks to their offspring by stretching their own necks throughout their lives, or that blacksmiths would have children with large musculature. We know this isn’t the way heredity works, and today I will discuss what happened when a whole nation adopted similar ideas in an ill-fated attempt to improve agricultural production to the detriment of the health of millions.
Can you get chocolate milk from brown cows? Believe it or not, during the cold war, Soviet scientists tried many experiments to achieve a very similar goal starting with plants. In 1927, an agronomist named Trofim Lysenko working at a remote agricultural station in Azerbaijan, published a report that winter varieties of wheat, which require a prolonged period of cold exposure in order to flower, could be permanently transformed into spring varieties that did not need cold exposure. The process required treating wheat seeds in moisture and cold, and was termed ‘vernalization’. Scientists had long since known that seedlings exposed to cold temperatures could be induced to flower within one season, however Lysenko’s main contribution was the idea that such a transformation could be inherited to the following generations without any treatment. By 1938 he had been named president of the Academy of Agricultural Science where he used his influence to enforce adherence to his ideas. Despite strenuous objections by the Russian scientific community, Lysekno’s ideas reached the ear of Soviet leaders and would become doctrine for decades. Several books have documented Lysenko’s rise to leadership, the interrelationship of his political leanings and scientific beliefs. The resultant purge of ideas and the scientists who advocated them serves as a lesson against political ideology influencing the scientific method.
Lysenko was a son of peasants with little education who rose to power on the strength of personality and ruthless denunciation what he termed “bourgeois science” by any means necessary. To wit, it is now known that he systematically faked data and field trials and denounced whole fields of science, such as statistics, that conflicted with his theories. In one famous exchange, Lysenko published a refutation of Mendel’s laws of inheritance that was criticized by the brilliant Russian statistician Andrey Kolgomorov. Lysenko responded by stating,
“We biologists do not take the slightest interest in mathematical calculations, which confirm the useless statistical formulae of the Mendelists … We do not want to submit to blind chance … We maintain that biological regularities do not resemble mathematical laws.”
By the early 1930’s, fifteen years after the Bolshevik revolution, Lysenko’s ideas had taken hold among the communist party elite in Moscow. He was convinced that Mendelian ideas of inheritance were contrary to Marxism because they implied necessary competition whereas he believed different species could thrive best by co-operating, leading to disastrous plans such as “cluster planting” which drastically reduced plant yields. As a result, the study of genetics ceased almost entirely in the Soviet Union until 1964 when Krushchev, who backed Lysenko, was deposed. Lysenko’s ideas were based in Lamarck’s belief in the inheritance of acquired characteristics, and adapted to fit Marxist ideology. The ideological tenants underlying Lysenko’s theories and their political consequences have been outlined in great detail in “The Lysenko Affair” by David Joravsky. Setting aside the political ramifications, what would science be like if Lamarckism had been taken seriously? How is it different from our modern concept of environmental modification of gene expression in epigenetics?
Given the premise of Lamarckism, with home-grown modifications, what sorts of results would a scientific community expect to be able to produce? Extending from his experiments with vernalization, Lysenko proposed that plants could be induced to change character in drastic ways. According to him, grafted plants would share characteristics in offspring. We know that there is some horizontal gene transfer between root stock and grafts, but these traits do not pass to seed. In his own scientific journal, he claimed to be able to adapt cotton and potatoes to be grown in far northern climes, a project also met with failure and shelved. Contrary to traditional practice of giving space to planted saplings, he claimed trees would grow best in clusters, with weaker saplings dying off for the good of their brethren (complete die-offs occurred instead.) He variously claimed that he could transform rye into wheat and barley, and that fertilizing hens with several cocks could create hybrid chickens. He even suggested at a conference that warblers gave birth to cuckoos by changing their diet. This all culminated in his claim to be able to increase the butterfat content of cow milk by breeding small Jersey cattle males with large local breed cows, or by feeding young cows diets high in fat, another experiment he was never able to carry out. His ideas rested on the ability of the zygote responding to its environment during development, as he stated, “The zygote is no fool.”
How are these ideas different from heritable epigenetic traits? In the case of the butterfat-producing cattle, he insisted that small bulls from breeds with high butterfat production must be mated to larger cows from local breeds in order to produce offspring with the butterfat trait, because the size of the offspring, and the butterfat trait, would be determined by the size of the mother, an idea that would come as a surprise to many animal breeders today. Lysenko rejected the idea of genes as the basis of heredity; indeed he ignored or was unaware of the discovery of DNA as genetic material as shown by Oswald Avery in 1944. Since epigenetic marks are generally chemical modifications of genes, controlling their expression, epigenetics relies upon the concept of genes. Epigeneticists today understand that there is a complex relationship between epigenetic marks and the genetic background, both being important to an organism’s response to environmental conditions and the limits of plasticity. Needless to say, no epigeneticist endorses the idea of transforming one species to another. Importantly, the epigenetic code is a layer on top of the genome, not separate information carrying entity, and its plasticity is subject to evolutionary pressures.
In the turn of the twentieth century, long before the rise of Lysenkoism, August Weismann had formulated the germ plasm theory, that heritable information can only be passed through the germ cells, and that use and disuse of somatic tissues cannot affect this germ plasm. The most dramatic experiment supporting this “Weismann barrier” involved the removal of tails of 5 generations of mice, all of whom continued to have offspring with tails, putting the final nail in the coffin of Lamarckism. Today our molecular methods allow us to interrogate the epigenetic marks of the “germ plasm” (i.e. sperm and eggs in animals) and discover the extent by which the environment can indeed affect these marks. We know that environmental changes by toxicant exposure, stress, nutrition, and other factors can alter the epigenetic marks of many body tissues, including the gametes, and so an intergenerational epigenetic effect can be seen. It is important to note, however, that these changes are considered non-Mendelian, but not Lamarckian, and that we have a molecular basis for understanding genetic and epigenetic changes. In my next blog post, I will cover some of the best-supported findings of epigenetic inheritance.
And how did this affect Soviet agriculture? Well peasant farmers had been unhappy with collectivization of farms and were even destroying grain to keep it from the Soviet government. The adoption of the “barefoot professor” Lysenko was supposed to encourage the peasants to re-engage in agricultural production. However his uncontrolled studies on wheat relied upon surveys from farmers about wheat production and were essentially fabricated to show ever increasing yields. As for his effects on Soviet science, the famed geneticist Theodosius Dobzhansky who immigrated to the US in 1927, once said that the party leaders were not idiots but had “taken the council of an idiot”. Historians note that nothing the US could have done would have been as effective in damaging Soviet research as Lysenko did himself. It was his rejection of genetics that allowed his theory of inheritance to stand, despite evidence to the contrary. In current research, epigenetics today explicitly relies upon genetics, the two are intertwined, standing upon the modern synthesis of evolutionary biology to achieve a greater understanding of the interaction of the genes and the environment.
1. DeJong-Lambert, W. The Cold War Politics of Genetic Research. (Springer Science+Business Media, 2012).
2. Gratzer, W. B. The Undergrowth of Science. (2000).
3. Pringle, P. The Murder of Nikolai Vavilov. (Simon & Schuster, 2008).
4. Joravsky, D. The Lysenko Affair. (University of Chicago Press, 2010).