A little over thirty years ago, during the
eighties, some of the fundamental concepts of evolution seemed to be quite
clear. Let us look at a few:
- The DNA of every living being
is an encrypted message that perfectly describes how to build the
corresponding phenotype (the adult individual). All the information is in
the genes. (Mechanistic reductionism).
- Most DNA is unnecessary (junk DNA) and has been accumulated due to
errors and repetitions in the transcription of the genomes of living
beings.
- The best metaphor to represent
the organization of a genome is a set of beads
on a string.
- Genes are the repositories of inheritance, and each gene
specifies a biological function.
- Evolutionary processes take
place through random mutations that act
on a single gene, which are subject to natural
selection, which results in small
incremental increases in the adaptation of living beings to
the environment.
As an example of this way of thinking we can
mention the novel Jurassic Park, by Michael
Crichton, which I mentioned in another
post in this blog. In this book, the possibility of obtaining DNA from
disappeared species (dinosaurs) is posed as something feasible in the immediate
future, by making them develop after injecting that DNA into the ovule of a
crocodile, which Crichton supposed would be sufficiently similar to the ova of
dinosaurs to make the process viable.
Just two decades later, at the beginning of the
21st century, biologist James
A. Shapiro described a completely different situation in an article
published in 2002 in the Annals of the New York Academy of Sciences:
- The DNA of living beings is an
integrated part of an extremely complex system, made of many inter-related
parts, many of which we do not know thoroughly. These parts interact to
build the phenotype of an adult individual (cybernetic
holism).
- There is no
unnecessary DNA or, at worst, there is a negligible amount. We don’t have a clear
idea of what many parts of the genome may represent.
- The most appropriate metaphor to
represent the organization of a genome is the
operating system of a computer. DNA plays a role similar to
the hard drive (a storage
device).
- Isolated genes do not make
sense. Complete genomes are the repositories of
inheritance, and can be considered as interactive
information systems.
- The most important evolutionary
processes are not random or gradual; they are reorganizations
of the genome, carried out under the control of the cell
itself, which is capable of rewriting part of its own DNA.
It will be seen that the picture has changed
completely. In this new environment, Crichton’s novel is just what it should
have always been, a fantasy game without the slightest possibility of becoming
real. It is evident that the ovule of a crocodile does not possess the
necessary epigenetic composition to make it possible for a dinosaur embryo to
develop there. In fact, such an attempt would be approximately similar to trying
to execute a program written for an operating system in a different and
incompatible one. Obviously impossible.
The concept of species should perhaps be
redefined taking into account these modern findings of biology. Thus, for instance,
the infertility of mules (hybrids of mare and donkey) may be due to the
epigenetic incompatibility of both species, whose DNA is close enough to enable
hybridization in the first generation, but not their subsequent proliferation.
Craig Venter |
A similar case is provided by the synthetic
biology experiment conducted by J. Craig Venter when his team transplanted the
DNA of a cell belonging to Mycoplasma mycoides to a cell of Mycoplasma
capreolus, two species of microorganisms with very simple genomes, quite
close to each other. The experiment was successful, so it was hailed as the first species change made experimentally by man through
genetic engineering. But it was only possible because these two
mycoplasmas are so similar, and their genomes so simple, that it is very likely
that both share the same epigenetic complex (the same operating system), in the
same way that they share a large part of their genes.
On the other hand, as I indicated in another post,
perhaps the concept of biological species should not be applied to bacteria, which
if confirmed would make us modify the categorization of Venter’s experiment.
Manuel Alfonseca
Fourth post in a series of four
Fourth post in a series of four
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