One of the biggest controversies in twentieth-century biology was about the inheritance of acquired characteristics, the ability of animals and plants to inherit adaptations acquired by their ancestors. For example, if a dog was terrified of butchers because he had been mistreated by one, his offspring would tend to inherit his fear. Charles Darwin wrote a letter to Nature describing just such a case. The opposing view, promoted by the science of genetics, asserted that organisms could not inherit features their ancestors had acquired; they only passed on genes that they themselves had inherited.

In Darwin's day, most people assumed that acquired characteristics could indeed be inherited. Jean-Baptiste Lamarck took this for granted in his theory of evolution published more than 50 years before Darwin's, and the inheritance of acquired characters is often referred to as "Lamarckian inheritance." Darwin shared Lamarck's assumption and cited many examples to support it in his book The Variation of Animals and Plants Under Domestication (1875).

Lamarck emphasized the role of behaviour in evolution. Animals developed new habits in response to needs, which led to the use or disuse of organs, which were accordingly either strengthened or weakened. Over generations, these changes became increasingly hereditary. Lamarck's most famous example was the giraffe. He thought giraffes' long necks were acquired through the habit of stretching up to eat the leaves of trees. In this respect too, Darwin agreed with Lamarck. For example ostriches, he suggested, may have lost the power of flight through disuse and gained stronger legs through increased use over successive generations.

The problem was that no one knew how acquired characteristics could be inherited. Darwin tried to explain it with his hypothesis of "pangenesis". He proposed that all the units of the body threw off tiny "gemmules" of "formative matter", which were dispersed throughout the body and aggregated in the buds of plants and in the germ cells of animals, through which they were transmitted to the offspring. This "Provisional Hypothesis of Pangenesis" appeared in the penultimate chapter of The Variation of Animals and Plants Under Domestication. Several modern theories of epigenetics are similar, but instead of gemmules they propose protein or RNA molecules.

Pangenesis was rejected by Mendelian genetics, the theory that dominated twentieth century biology in the West. Heredity was genetic, not Lamarckian or Darwinian. The neo-Darwinian theory of evolution differed from the Darwinian theory by rejecting the inheritance of acquired characteristics. Neo-Darwinism became the ruling orthodoxy in the West from the 1930s onwards. Lamarckian inheritance was treated as heresy.

Meanwhile, in the Soviet Union the inheritance of acquired characteristics was the orthodox doctrine from the 1930s to the 1960s. Under the leadership of Trofim D. Lysenko, much Soviet research on inheritance supported the inheritance of acquired characters. Stalin favoured Lysenko, and geneticists were persecuted. This Stalinist approach increased the opposition to the inheritance of acquired characteristics in the West. The nature of inheritance became intensely politicized. Ideology, rather than scientific evidence, dominated the dispute.

The Western taboo against the inheritance of acquired characteristics began to dissolve around the turn of the millennium. There is a rapidly growing body of evidence that acquired characters can indeed be inherited. This kind of inheritance is now called "epigenetic inheritance." In this context, the word epigenetic signifies "over and above genetic." Some kinds of epigenetic inheritance depend on chemical attachments to genes, particularly of methyl groups. Genes can be "switched off" by the methylation of the DNA itself or of the proteins that bind to it.

This is a fast-growing field of research, and there are now many examples of epigenetic inheritance in plants and animals. For example, in a recent study with mice, the fears of the fathers were passed on to their children and grandchildren. Male mice were made averse to the smell of a synthetic chemical, acetophenone, by being given mild electric shocks when they smelled it. For at least two generations, their offspring reacted with fear to this smell, even though they had never been exposed to it before.

In the mid-twentieth century, Lysenko and other Soviet biologists were demonized in the West for affirming an inheritance of acquired characteristics in animals and plants. Western biologists assumed that this Soviet research must be fraudulent. But in the light of epigenetics, can we be sure that almost all the papers on inheritance published in the USSR were wrong? Were all Soviet scientists totally brainwashed? Or were some of them sincerely reporting what they found? Among the many thousands of papers in Soviet biology journals, there may be seams of gold. No doubt these journals are still available in scientific libraries. If Russian-speaking biologists reviewed this literature they might unearth great treasures.