Species as Individuals in the Hierarchical Theory of Selection 693
either because bodies don't "notice" the increase (at least while the number of genie
copies remains "within bounds"), or because higher-level selection also benefits
from such differential genie proliferation (if, for a hypothetical example, an X-
driving chromosome helped to generate the female bias that inter-demic selection
also favored)—then genie selection can be quite rapid and powerful. This general
phenomenon, perhaps of great importance in evolution, has acquired the
unfortunate name of "selfish DNA," as designated in two seminal papers,
representing independent and simultaneous discovery, and published back to back
in Nature in 1980 (Orgel and Crick, 1980; Doolittle and Sapienza, 1980). These
authors proposed that such genie selection, orthogonal (at first) to organismal
selection, might account for most of the middle-repetitive DNA—some 15 to 30
percent of the genome in humans and Drosophila, and usually existing as tens to a
few hundred copies per sequence, with copies often widely dispersed among
several chromosomes.
Other hypotheses might explain this phenomenon, particularly as a potential
organismic need for enhanced levels of any products ultimately made by any gene.
(In a purely organismal view, all genes may be able to proliferate, but not to fix
their multiple copies unless organismic selection favors the increase. However, the
two levels might also act synergistically, with genie drive evolving only in some
genes, and for Darwinian benefit at this basal level, but with proliferation then
enhanced by positive organismic selection upon bodies carrying more copies).
The "selfish DNA" hypothesis includes an attractive feature, rooted in the
hierarchical theory of selection, for explaining stabilization of copy number at tens
to hundreds, rather than an ultimately suicidal proliferation to inevitable death of
the organism and all gene-individuals contained therein. Genie selection may begin
in the orthogonal mode, as initial increases impose no consequences upon the
phenotype. But organisms must eventually take notice, if only for the energetic
drain, and presumed slowing of ontogenetic development, imposed by replication
of so many unneeded copies with every cellular division. Original orthogonality
must therefore eventually yield to a situation of genie selection contrary to
organismal interest. At this point, negative selection at the organismic level should
stabilize and limit further increase—the presumed explanation, within the theory,
for the intermediary copy number of middle-repetitive DNA.
Although I regard the hypothesis of "selfish DNA" as powerful, probably
correct in many cases, and therefore as our best argument for substantially
important selection at the genie level, two features in its initial promotion distress
me because they embody (without conscious intent, I assume) the persistent
parochialism of organismic bias, even among those who explicitly promote the
hierarchical alternative. First, consider the unfortunate choices of names.
Proliferating genie elements have generally been called "outlaws," "renegades," or
"parasites"; and the general phenomenon entered our literature as the hypothesis of
"selfish DNA." Orgel and Crick imposed a double whammy of opprobrium in the
title of their original article: "Selfish DNA: the Ultimate Parasite." The only reason
that I can imagine for such derogatory