Epigenesis

Epigenesis can have different meanings depending on the scientific discipline that explains it:

Biology

Definition

In biology, epigenesis (from the Greek epi: about; genesis: generation, origin, creation) is an ancient theoretical proposition about the method by which an individual develops: an embryo develops from an egg/zygote that has not differentiated. That is to say, there are no miniature components of pre-existing organs in the gametes (egg or sperm), this theory is opposite to the so-called "preformation". Epigenesis predicts that the organs of the embryo are formed from nothing, through induction by the environment.

The paradigmatic case is that of growth, in which a complex cellular and organic structure develops from a zygote. By extension, systems theory includes the mechanisms that allow a given individual to modify certain aspects of its internal or external structure as a result of interaction with its immediate environment.

Epigenesis therefore represents the process of "tuning" final process through which each individual adapts efficiently to its environment based on the capabilities contained in its genetic code. Genes are part of a complex network of interactions that feed on each other and, therefore, do not act as independent identities.

The most obvious examples of systems with the capacity for learning following the epigenetic theory are the central nervous system or the immune system. In the case of the central nervous system, the learning capacity (given by the great neuronal plasticity) is of vital importance, since the estimated number of synaptic connections in a human brain far exceeds the number of nucleotides contained in the human genome (in On average, a single neuron in the human brain has 50,000 synapses).

History

There was a debate from the epigenetic vision confronting the "preformation", which assumed the organs present in miniature form within one or both gametes. Preformationism ended in the mid-1820s when technology was able to document the epigenetic origin of organs. This debate was historical (a brief and concise history will be shown): Aristotle, in The Generation of Animals (350 BC), proposed epigenesis as a method of development of embryos. William Harvey, in 1651, supported the view of the impact of the environment on the development of the embryo. In 1672, Marcelo Malpighi doubted epigenesis when he observed that the unincubated chicken egg had a large amount of structure. Kaspar Friedrich Wolff, in the second half of the 18th century, revived the epigenetic theory by demonstrating that structures present in the adult chicken did not have their counterpart in the embryo.

Immanuel Kant and Johann Friedrich Blumenbach made an attempt to reconcile the two theories by postulating a developmental force (Bildungstrieb) that was inherited through the germ cells. This view is similar to that of modern biologists, where the instructions for developing the entire organism are present in the egg. The most prominent scientists who revolutionized developmental biology and put an end to the theory of preformation were three friends: Christian Pander, Karl Ernst von Baer and Heinrich Rathke. With them, developmental biology became a specialized scientific discipline.

References

• Gilbert, S. F. (2006). Developmental Biology (Eighth ed.): Sinauer Associates, Inc.
• Løvtrup, S. R. (1989). Recapitulation, epigenesis and heterochrony. [doi: DOI: 10.1016/S0016-6995(89)80028-2]. Geobios, 22(Supplement 2), 269-281.
• Mazzocchi, F. (2010). Complementarity in biology. [JOUR]. EMBO Rep, 11(5).
• Oxford. The New Oxford American Dictionary (Ed.) (2005) (Second ed.). New York: Oxford University Press, Inc.
• Zammito, J. H. (2003). [`]This inscrutable principle of an original organization': epigenesis and [`]looseness of fit' in Kant's philosophy of science. [doi: DOI: 10.1016/S0039-3681(02)00092-4]. Studies In History and Philosophy of Science Part A, 34(1), 73-109.

Geomorphology

In geomorphology, epigenesis is the phenomenon in the course of which a river, whose bed is excavated in a mantle of soft rock, carves a canyon in the underlying hard rock. The interposition of this in a stretch of the watercourse may be the result of an antecedent: the hard rock structure has been enhanced by tectonic movements subsequent to the installation of the river in the soft terrain. In other cases it is a phenomenon of superimposition: the hard structure already existed and had acquired its shape under the soft rock before the installation of the river.

Mineralogy

In mineralogy, epigenesis is the change in the chemical nature of a mineral without modifying its previous structure and shape. Petrification, a particular case of organic epigenesis, constitutes an ideal example of this phenomenon: the trunk in which the matter has been replaced by silica preserves the structure of the fibers, rings and knots of the wood.