Lamarck and Epigenetics
Jean Baptiste Lamarck was a war hero, a botanist, a pioneer in the field of invertebrates, a writer, and a scholar. He died blind and impoverished in 1829, never having gained respect or popularity from the scientific community, and today is remembered only for having wrongly conceived of evolution. He was buried in a rented grave and five years later his remains were removed and lost forever. But his ideas will perhaps soon be at the forefront of a new evolutionary debate.
As a biology student studying evolution, I’ve become very loyal to a neo-Darwinian understanding of evolution. Random genetic mutations and recombinations due to sexual reproduction lead to variation. Some variations will be advantageous to an organism, either by increasing the likelihood of survival to reproductive age or by increasing the chances of finding or attracting a mate. These advantageous variations will therefore be passed on to offspring and preserved.
I recently came across a field of study called epigenetics. I am the first to admit that I do not have a very thorough understanding of this field. However it seems to imply that in some circumstances, certain traits acquired by an individual during its lifetime can be inherited by several generations of offspring. Epigenetic inheritance might be defined as the heritability of changes in phenotype that are not due to changes in DNA sequence of but instead regulation of DNA expression.
Two Israeli researchers put together a list of over a hundred examples of epigenetic inheritance sustained for multiple generations.
Exposing Ciliate (a protist) to extreme heat, salinity, and arsenic induces a tolerance for these conditions that is inherited for several generations before fading away.
In a certain type of fungus, Candida albicans, a spontaneous change in cell morphology, colony-forming ability, and mating properties thought to be affected by temperature, was heritable for 10,000 generations.
In sugar beets the mode of reproduction and climatic conditions can change the types of flowers, the ability of self-fertility, and the number of chloroplasts, and these changes last for two generations or more.
In wheat exposure to nicotinic acid causes longer reproductive spikes and larger seed. That change is heritable for 57 generations.
Exposure to high temperatures causes a change in the eye color of fruit flies that is heritable for at least 4 generations. High temperature exposure also causes a suppression of wing deformations in these flies that is heritable for an undetermined number of generations, though probably at least two.
Piebald spotting in domesticated foxes, possibly caused by hormonal stress, is inherited for 2 or more generations.
The grandchildren of boys exposed to famine in Sweden were less likely to die of heart disease.
“All the acquisitions or losses wrought by nature on individuals, through the influence of the environment in which their race has long been placed, and hence through the influence of the predominant use or permanent disuse of any organ; all these are preserved by reproduction to the new individuals which arise, provided that the acquired modifications are common to both sexes, or at least to the individuals which produce the young.”
Except for the “all” and maybe the bit about disuse of organs, this quote seems to be a fairly accurate description of epigenetics, at least for the examples listed above. In fact many epigenesists are looking towards a new, hybrid theory of evolution incorporating Darwinian and Lamarckian principles with science’s growing understanding of the complex inner-workings of organisms. What exactly this hybrid theory would say I’m not sure. Sometimes variation is random. Other times it seems to be caused by environmental conditions. Is epigenetic inheritance a rare phenomenon? Some scientists argue that it is ubiquitous, others that is found only in specific genes. Could it have evolved through natural selection and random variation? It is conceivable to me that offspring with the ability to somehow inherit an acquired trait of their parents would often have an advantage and therefore be selected for, thought how the ability first arose I have no idea. Perhaps it was through the random variation I know and love.
Speaking of Randomness, Darwin wrote:
“I have hitherto sometimes spoken as if the variations … were due to chance. This, of course, is a wholly incorrect expression, but it serves to acknowledge plainly our ignorance of the cause of each particular variation.”
I am fond of the idea of randomness, and am confident in the ability of science to lessen our ignorance. However, the idea of epigenetics and the heritability of acquired traits has be befuddled, so I will end with a question. Does the fact that we now have what seem to be several examples of variation directed by the environment change how we feel about the randomness of evolution?