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jor changes. Susumu Ohno, who first 
popularized this idea in 1970 in a bril- 
liant book ( Evolution by Gene Duplica- 
tion), argued that, without redundancy 
“from a bacterium only numerous forms 
of bacteria would have emerged.” Du- 
plication supplies the raw material of 
major evolutionary change: “The cre- 
ation of a new gene from a redundant 
copy of an old gene is the most impor- 
tant role that gene duplication played in 
evolution.” 
But think about it for a moment. The 
argument is sound and may represent, in 
fact, the major effect of gene duplica- 
tion for evolution. Yet unless our usual 
ideas about causality are running in the 
wrong direction, this flexibility simply 
cannot be the adaptive explanation for 
why repetitive DNA exists. Selection 
works on individuals at the moment. It 
cannot sense what may be of use ten 
million years hence in a distant descend- 
ant. The duplicated gene may make 
future evolutionary change possible, but 
selection cannot preserve it unless it 
confers an “immediate significance.” 
Future utility is an important consider- 
ation in evolution, but it cannot be the 
explanation for current preservation. 
Future utilities can only be the fortu- 
itous effects of other direct reasons for 
immediate favor. 
(The confusion of current utility with 
reasons for past historical origin is a 
logical trap that has plagued evolution- 
ary thinking from the start. Feathers 
work beautifully in flight, but the ances- 
tors of birds must have evolved them for 
another reason — probably for thermo- 
regulation — since a few feathers on the 
arm of a small running reptile will not 
induce takeoff. Our brains enlarged for 
a set of complex reasons, but surely not 
so that some of us could write essays 
about it. Interested readers may wish to 
consult a technical article, to appear in 
Paleobiology during 1982, that Elisa- 
beth Vrba and I have written about this 
subject. We wish to restrict the term 
adaptation only to those structures that 
evolved for their current utility; those 
useful structures that arose for other 
reasons or for no conventional reason at 
all, and were then fortuitously available 
for other usages, we call exaptations. 
New and important genes that evolved 
from a repeated copy of an ancestral 
gene can only be exaptations, and their 
new usage cannot be the reason for the 
original duplication.) 
The second set of adaptive arguments 
is legitimate in proposing an immedi- 
ate selective benefit for repeated DNA. 
If genes move about and insert them- 
selves on different chromosomes, for ex- 
ample, they may occasionally link up 
with other segments of DNA to form 
advantageous new combinations. More 
importantly, much DNA, while not cod- 
ing for protein itself, may play a role in 
regulating the DNA that does. This 
regulatory DNA may turn other genes 
on and off and may determine the se- 
quence and location of expression for 
the genes that do code for proteins. If 
repetitive DNA performs these regula- 
tory functions, then its dispersal 
throughout the genome can have pro- 
found immediate effects. Inserted into a 
new chromosome, it may turn adjacent 
genes on and off in new ways and se- 
quences. It may, for example, bring 
together the products of two genes that 
had never been in proximity. This new 
combination may benefit an organism 
(see the classic article of Roy Britten 
and Eric Davidson, Quarterly Review of 
Biology, 1971, pp. 111-31). 
Yet, for all these efforts, the nagging 
suspicion remains that these adaptive 
explanations cannot account for all re- 
petitive DNA. There is simply too much 
of it, too randomly dispersed, too appar- 
ently nonsensical in its construction, to 
argue that each item perseveres because 
natural selection had favored it in a 
regulatory role. The selfish DNA hy- 
pothesis proposes a fundamentally dif- 
ferent explanation for much of this rep- 
etition. It is radical in that literal sense 
of getting to the roots, for it demands 
that we reassess some basic and usually 
unquestioned assumptions of evolution- 
ary argument — what Orgel and Crick 
meant when they spoke of facts “so odd 
that only a somewhat unconventional 
idea is likely to explain them.” 
The argument is simplicity itself once 
you establish the frame of mind to per- 
mit it: if repetitive DNA is transposable, 
then why do we need an adaptive expla- 
nation for it (in conventional terms of 
benefits to bodies) at all? It may simply 
spread of its own accord from chromo- 
some to chromosome, making more 
copies of itself while other “sedentary” 
genes cannot. These extra copies may 
persist, not because they confer advan- 
tages upon bodies, but for precisely the 
opposite reason — because bodies do not 
notice them. If they have no effect upon 
bodies, if they are (in this sense) “junk,” 
then what is to stop their spread? They 
are merely playing Darwin’s game, but 
at the wrong level. We usually think of 
natural selection as a struggle among 
bodies to leave more surviving offspring. 
Here certain genes have found a way, 
through transposability, or “jumping,” 
10 
