Can our children inherit traits which we acquire during our

Already half a century ago, the American biologist Tracy Morton Sonneborn (1905 - 1981) observed that the single-cell animal Paramecium aurelia can transmit acquired surface scars to its offspring. During sexual reproduction, two Paramecium partners line up side by side and form a tunnel between them through which they exchange their DNA. When they separate again, each partner regains its normal surface. But sometimes this separation is faulty and one partner retains a snippet of the other's surface.

Already half a century ago, the American biologist Tracy Morton Sonneborn (1905 - 1981) observed that the single-cell animal Paramecium aurelia can transmit acquired surface scars to its offspring. During sexual reproduction, two Paramecium partners line up side by side and form a tunnel between them through which they exchange their DNA. When they separate again, each partner regains its normal surface. But sometimes this separation is faulty and one partner retains a snippet of the other's surface. This scarred surface structure is then transmitted faithfully to the offspring for many generations. Similarly, if yeast cells are briefly exposed to a certain sugar, they change their metabolism in order to use this sugar as food. When the sugar is then removed, the cells "remember" how to digest the sugar and pass on this memory for hundreds of generations. Neither of these heritable changes involves changes in DNA: In the case of Paramecium, the cell surface appears to function as a template for making an identically structured new surface; and in the case of yeast, the heritable change is probably a locked-up metabolic state from which neither the original cell nor its offspring can escape..

But sometimes the environment can even change the genome in a "purposeful" way. When the plant Arabidopsis is irradiated with harmful ultraviolet light, it starts to repair and remodel its DNA at an increased rate in an attempt to undo the ultraviolet damage. Amazingly, it continues to do so for several generations after the ultraviolet light has been turned off. And when certain bacteria are challenged by heat or by poisons, the rearrange parts of their DNA in an attempt as to generate novel types of defense proteins. It is not yet proven, but likely, that we humans may also adapt parts of our genome in a directed way and then pass on these changes to our children. In lower organisms, such heritable "epigenetic" changes involve attachment of chemical groups to DNA, or modification of proteins with which the DNA is packaged into chromosomes.

The French biologist Jean-Baptiste de Lamarck (1744 - 1829) had proposed more than two centuries ago that evolution proceeds by the genetic transmission of acquired properties. The Soviet agronomist and charlatan Trofim Denisovich Lysenko (1898 - 1976) ruthlessly enforces this view as Soviet dogma, because it suggested the possibility of breeding a new generation of citizens genetically adapted to Soviet society. Today we know that this is not how evolution normally works. But sometimes it makes exceptions which prove the rule.

The concept of evolution is probably the greatest intellectual achievement of humankind. Without this concept, nothing about life makes any sense. Evolution explains not only the amazing diversity of living organisms, but also their almost limitless ability to adapt to changes in their environment. Charles Darwin (1809 - 1882) and Alfred Russel Wallace (1828 - 1913) presented their revolutionary concept of evolution to the Linnean Society of London in 1858, and one year later Charles Darwin explained it at length in his historic book "On the origin of species by natural selection". At that time, neither genes nor DNA had yet been discovered. Had Darwin and Wallace known about them, they would have said hat evolution proceeds by random mutation of an organism's DNA, followed by selection of those mutants that can best multiply in their habitat. While the environment may cause mutations, it has no influence on how these mutations affect the organism. In other words, evolution involves "blind" mutation followed by "purposeful" selection.

This concept of evolution is still correct, but there are some exceptions. These are very rare and in no way invalidate the concept. But they spice it with a healthy dose of heresy. Science always tries to reexamine generally accepted theories in the light of new evidence. It never gives us "absolute truths", but explanations that best fit existing knowledge.