Control Systems in the Living World - Building the Most Complex Structure on Earth - page 6

circumstances can a protein, gene, or genome, or any combination of them, function
as a living system; only a cell can (or at least a cell of a unicellular organism can).
As pointed out earlier, the ability of the control system of an organism to monitor
the structure, to identify deviations from the norm and send instructions for restor-
ing the norm, clearly shows that it has information on the structure and is capable of
transmitting that information to the offspring.
Unicellulars reproduce via binary fission or sexual reproduction. In strict terms,
their reproduction does not fit well into the conventional mother-to-daughter repro-
duction scheme. Cell division does not produce two “daughter” cells; the result
of the division is only two cells, rather than three. It would not be correct to say
that it produces one daughter cell, because the semiconservative mechanism of cell
duplication, from both the genetic and epigenetic viewpoint, makes it impossible
to determine which of the cells resulting from cell division is the mother or daugh-
ter. Hence, each of the resulting cells is the twin of the other. Cell division, thus,
leads to production of two “twin cells.” Each of the twin cells is equally ancestral
to, and descendant of, the other. The distinction can be clear only at the generational
level, where we can speak of successive generations or ancestral and descendant
generations.
From this viewpoint, unicellular forms also defy our traditional dichotomic con-
cept of death and life—unicellular forms of life virtually are potentially immortal—
the dividing cell does not die, but half-lives in the structure and functions of the two
cells of the next generation. This semantic aspect aside, what is essential is the fact
that in unicellulars, the two sister cells after division are fully capable of independent
life and reproduction, which is in marked contrast with what is observed in multicel-
lular organisms.
The epigenesis-preformation dichotomy also seems hardly applicable in the case
of the reproduction of unicellular organisms. Transformation of an original organ-
ism into two implies quantitative change; that is, duplication of existing cell mass,
including duplication of the genetic information and epigenetic information con-
tained in epigenetic structures of the unicellular organism.
At the multicellular level of organization, biological systems shifted from the
reproduction mode of unicellulars. They do not reproduce semiconservatively,
producing a twin of themselves within the existing system and sharing its original
structure with it, as unicellular organisms do. The basic mode of reproduction in
multicelllulars—sexually and nonsexually reproducing multicellulars alike—is via
gametes. Theirs is an epigenetic mode of reproduction that comprises both qualita-
tive (biological development) and quantitative (growth) changes via the sequential
steps of cell differentiation, organogenesis, and morphogenesis of the egg/zygote
into an adult organism.
The idea that multicellulars produce copies of themselves is also controversial.
What we actually observe are gametes, eggs, and sperm cells (eggs only in parthe-
nogenetic organisms), or newborns that follow an independent complex development
until they become “copies” of their parents. Parents provide gametes with the epige-
netic information necessary to develop to an early embryonic stage, the phylotypic