Development: Three Grades of Ontogenetic Involvement 183their retention from one generation to the next and their subsequent selection. The
iterated cycle of inheritance and selection requires that the processes of ontogeny
transmit the heritable variants reliably. But, apart from that, ontogeny plays
no significant role in the creating or fixing either the diversity of organisms or
generating their adaptedness.
So we have three distinct processes, development, inheritance and adaptation,
each with a significant degree of autonomy. Adaptive evolution requires all three.
Without selection, there is no evolutionary change. But selection requires the
reliable recurrence (inheritance) of traits, and a source of new variants. The process
of Mendelian inheritance meets these requirements. But variants are selected
through their contribution to the survival and reproduction of entire organisms.
Ontogeny is the process that delivers Mendelian factors, embodied in organisms,
to the arena of selection.
3 SUB-ORGANISMAL BIOLOGYThe fragmentation of evolution into three independent processes also calls for an
account of what unites them into a single process of adaptive evolution. The
concept of the replicator plays this unifying role in orthodox versions of current
biology. Replicators are the only units of biological organization that take part
in all the constituent processes of evolution, and whose causal capacities unite
these processes into the process of evolution. (i)Inheritance: Replicators, we
are told, are the units of inheritance. They are the only entities that are both
copied within parents and transmitted from parent to offspring in reproduction.
(ii)Ontogeny: Development, according to the sub-organismal view, is simply the
implementation of a developmental program, the decoding of phenotypic informa-
tion encoded, in the replicators (e.g. [Maynard Smith, 2000]). Organisms may be
what are selected, but it is replicators that build the organisms that are selected.
(iii)Adaptation: Adaptive evolution by natural selection occurs when populations
change their structure as a consequence of the differential survival and reproduc-
tion of organisms. But not just any old change in population structure counts as
evolutionary change — even a change that increases the average adaptedness of
individuals in the population — adaptive evolution occurs, we are told, only when
the relative frequency of replicators change. Indeed natural selection is usually
definedas changes in replicator frequencies that result from the differential con-
tribution of replicators to survival and reproduction [Bell, 2000]. Replicators are
not only the causes of evolution, they are its currency.
The most thorough and provocative exponent of sub-organismal biology is
Richard Dawkins:
Evolution is the external and visible manifestation of the survival of
alternative replicators... Genes are replicators; organisms... are best
not regarded as replicators; they are vehicles in which replicators travel
about. Replicator selection is the process by which some replicators