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Cell recursion theory states that recursive functions running between dividing cells of a growing embryo is the basis of the mechanism to explain the emergence of complex forms in animals and plants because of an elaborated capacity of computation of their genomes. In The origin of Metazoa: an algorithmic view of life, it has been proposed that during embryogenesis, cells that contain an identical genome generate different instances of themselves just like recursive computer programs do.
The theory is based on a model that attempts to explain the origin of animal and plant forms (and the associated mechanisms of evolution) with the complexity of metazoan genomes. According to this theory during embryogenesis the genetic information is retrieved from DNA with a mode of operation similar to computers. Essentially, the theory claims that a highly significant analogy between genome and computer architectures exists that is based on the presence of a higher level of hierarchy in genomes of metazoa and plants whose existence had been overlooked so far.
The Cell Recursion Theory is based on the assumption that genomes of higher organisms have the capacity to compute that and a growing embryo is similar to a Turing machine. Such a notion had been also proposed by
Nobel laureate Sydney Brenner who has argued that Turing machines and cells have much in common thus appealing to the development of a new, unifying
theoretical foundation. Brenner also stated that: “Biology urgently needs a theoretical basis to
unify it and it is only theory that will allow us to convert data to knowledge.”
Most molecular biologists/evolutionary biologists have equated the
mechanisms of gene regulation during embryogenesis to a “Turing
machine”, assimilating the developmental process occurring during
embryogenesis to sequential Boolean logic gates
; . However, these models do not describe the necessary presence
of an external reference point that allows an embryo to proceed during
differentiation from one “logic gate” to the next.
Cell Recursion Theory proposes that such an external reference point does exist and is determined by telomere (short stretches of repetitive units of DNA located at the ends of any linear chromosome of eukaryotic
cells) shortening that occurs at each cell division. Thus, cells of metazoan organisms have been conceived as “Universal Turing machines“ acknowledging their capacity to define recursive functions necessary to express topology, i.e. complex animal and plant forms. Since lower eukaryotes do not experience telomere erosion and bacteria do not have telomeres at all (they posses a circular chromosome), they cannot express multicellularity. Thus, this theory is based on the capacity of genomes of higher organisms to express recursion and on Gödel’s theorems of incompletness .
Fractals
Multicellular organisms, such as plants, and various metazoan organs, such as kidneys and lungs, express typically self-similar patterns (fractals), as well as other recursive structures. Since fractal geometry is a heritable property of biological organisms, and fractality is a process of recursion, it must be coded in their genomes. Plants (e.g. shapes of trees, distribution of leaves in plants) , and organs , such as kidneys and lung
airways of
metazoans, have typically self-similar patterns (= fractals), as well as
other recursive structures (blood vessel growth) . However, differently
from fractals originating in the physical world (e.g. coast, clouds or
mountain contours) result from physical laws and are
described a posteriori by fractal mathematics., fractal geometry is a
heritable property of biological organisms, and, therefore, the ability
to express fractals is likely coded in their genomes. Thus, fractals of
living organisms appears to emerge from within the organism, which would
necessitate a capacity for computing similar to computer software.