In my articles on zygotes and embryos, I mentioned non-genetic factors that play crucial and significant roles in the development of individual organisms; one of those processes I mentioned was epigenetics, which I alluded to in one sentence. In reality, such a brisk glossing over does this very important and complex subject no justice, so I have decided to pen this present article to cover this topic, in particular.
What is epigenetics? To understand, we need first to cover what genes and genomes are. Genes are portions of DNA (Deoxyribonucleic Acid), the nucleic acid macromolecule inherited from an organism's ancestors. Each individual gene is like an instruction to produce a particular characteristic, and the entire set of genes in the DNA, all taken together, is known as a genome. The process of how these instructions actually create the structures that they code for is known as gene expression. This is where epigenetics comes in. Epigenetics is the process of controlling and modfying how genes are expressed during the process of gene expression.
This seemingly innocuous fact has wider implications, for it shows that, thanks to epigenetics, it is truly inaccurate to say that we, as individual organisms, are the products of our genes alone, and that our genes represent our destinies. In reality, we are the products of genes, as well as processes such as epigenetics, which result in non-genetic factors, including other components of the cell, such as cytoplasm, and external factors in the environments inhabited by us, playing a critical role in shaping who we are as individuals.
Another important aspect of epigenetics to note is that it is, to some extent, heritable. At the time of fusion of the gametes, ovum and sperm, the resulting offspring inherits an epigenome (a set of epigenetic factors somewhat analagous to the genome, which is composed of genes, hence the name) from both of its parents.
Yet another important aspect of epigenetics is that, in addition to being heritable, unlike genes (which generally remain fixed throughout an individual organism's life cycle), epigenetics can be altered by an individual's experiences in their life, and this altered epigenome can then subsequently be passed down to offspring at the time of reproduction. In other words, changes to the epigenome incurred during an organism's life are heritable, allowing them to be existent in the offspring of said organism from the time of said offspring's conception.
An organism's epigenome is modified by its environment and experiences throughout its life, from the time it is conceived by the fusion of each of its parents' gametes to the time of its death.
This process of changes to an individual's phenotype brought on by an individual's life experiences that are subsequently inherited by its offspring is quite reminiscent of Lamarckism, a hypothesis regarding how evolution worked proposed by Jean-Baptiste Lamarck, positing that, for example, a giraffe stretching its neck, lengthening it slightly, to reach the tallest leaves on a tree would bear children with slightly longer necks than it, and so on, until, over time, the giraffe population, as a whole, became long-necked. This hypothesis was adopted by many early proponents of evolutionary theory, including noted American paleontologist Edward Drinker Cope, but was generally discredited once Charles Darwin's theory of evolution by natural selection arrived on the scene.
However, epigenetics has, in a sense, resurrected Neo-Lamarckism. In addition to noting this, it should also be noted that, according to recent discoveries, even phenomena normally thought to be entirely the providence of the nervous system, such as memories, might fall under the purview of epigenetics. I am planning to devote another full article to this later, but I think it shall suffice to say here that the existence of a phenomenon known as cellular memory, the ability of cells, including some besides those of the nervous system, to record information incurred during an organism's lifetime in the form of memories, has begun to be supported by studies. This means that experiences that were endured by an individual's ancestors and which left their imprints in said ancestor's cells were passed on to their descendants in the form of their gametes, meaning that even things such as memories could be, to some extent, heritable, in a sense, due to epigenetics.
Overall, epigenetics is among the most fascinating frontiers in the field of developmental biology and genetics, and research on it is still in its early stages. In the future, more research could shed light on this wonderfully intriguing, and strikingly imperative, area of biology.