Jean-Baptiste Lamarck has long been debunked. Or so the story goes. Lamarck formulated the theory that the environment shapes genes, and that these changes are passed on to your children; on other hand, Darwin argued that genes are not changed by the environment and formulated natural selection. Lamarckian evolution theories on environmentally acquired characteristics are often referenced and contrasted with Darwinian evolution, but mainly for the sake of showing just how right Darwin was. It is true that Darwin’s theories have stood the test of time and rightly so, as his ideas of natural selection have shaped how we view biology and evolution. Yet, Darwin became engrossed with Lamarck’s ideas later in life and is said to have died “almost a Lamarckian” . He went so far as to begin to formulate his own theory of acquired characteristics, which he called the “conditions of existence” . Darwin’s later theories agreed with Lamarck on the importance of environmental inputs.
Both of these giants seemed to be in agreement, but how these acquired characteristics translated into genetic code remained unclear. The solution that emerged was epigenetics. Epigenetics is a phenomenon with many complex implications, but thankfully, one that can be easily summarized. DNA is modified though methylation or acetylation, which turns gene expression on or off through the activation or inhibition of transcription. Methylation is generally associated with inhibition while acetylation is associated with activation, and both are common epigenetic phenomena.
These epigenetic changes are transferred in the somatic cell line as a part of normal DNA replication. This is generally temporary since only changes in the germ line gametes affect the next generation, but recent research has shown that some epigenetic modifications can be passed down . The geneticist Marcus Pembrey goes so far as to say that even factors such as nutrition or stress can affect your descendants . The implications of this assertion are astounding: the choices you make right now, in this minute, have a chance of affecting your children. What you eat will eventually change your genes and those genes might just get passed down to your children. This is a sobering thought, more so because we are not aware of all the details of the underlying mechanism. The environment and how you react to it are important after all. This is an expansion of Darwinian thought, the synthesis of Darwin and Lamarck.
We now know a great deal about mammalian epigenetics, including its important role in early development . DNA methylation is especially important in the germ line. These epigenetic markers often supplement transcription factors, which are proteins which enter the nucleus to modify the expression of genes that code the program for normal development.
This mystery of what triggers the initial methylation events will no doubt confound scientists for years to come, but it is still remarkable that so much is known about epigenetic pathways. Epigenetic tags are often removed in a newly fertilized egg, especially because the sperm is often hypermethylated, but some tags remain [2, 3]. While the mechanism by which these tags are not removed is not certain, research points to hydroxymethylation as the candidate for transgenerational inheritance .
If this is the case, this will change how we look at genetic diseases. Epigenetics has added a new layer of complexity to how we look at inheritance. The study of diseases will expand from direct examination of genes transferred from parent to offspring to include examination of the epigenetic tags on those genes and those associated with diseases. There already exist several ways to look at epigenetic markers in the cell and the methylome, the collection of all the methyl markers in a cell, will soon take its place next to the transcriptome and proteome in importance .
One new way in which epigenetics affects everyday life is the development of allergies. New evidence has shown that allergies originate in the early phases of development . A maternal diet rich in methyl donors has been associated with the development of allergies in the offspring. This methylation in the maternal genome, once present in germ line cells, could potentially affect T-cell differentiation in the offspring, which might have consequences for the occurrence of allergies . This indicates that diet, especially during the crucial development window, can have long-term effects.
Epigenetics has wide-reaching implications on human disease and human development. Lamarck turned out to be right, though his theories did not capture the full complexities of genetics; for that matter, neither did Darwin’s. Only by accepting the theories of both major figures and by synthesizing them do we arrive at the next breakthrough in genetics.
1. Marsh, David. Darwin’s passionate environmentalism or the dangerous fallacy of the ‘All-sufficiency of natural selection’ theory. Nutrition and Health January 2012 21: 76-90.
2. Smith, Z. D. and Meissner, Alexander. DNA methylation: roles in mammalian development. Nature Reviews Genetics 14, 204-220 (March 2013).
3. North, M. L. et al. The role of epigenetics in the developmental origins of allergic disease Annals of Allergy, Asthma & Immunology, Volume 106, Issue 5, May 2011, Pages 355–361.