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Science Frontiers ONLINE No. 94: Jul-Aug 1994 |
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Our genes aren't us!
Almost without exception, biology textbooks, scientific papers, popular articles, and TV documentaries convey the impression that an organism's genes completely specify the living animal or plant. In most people's minds, the strands of DNA are analogous to computer codes that control the manufacture and disposition of proteins. Perhaps our current fascination with computers has fostered this narrow view of heredity.
Do our genes really contain all the information necessary for constructing human bodies? In the April 1994 issue of Discover, J. Cohen and I. Stewart endeavor to set us straight.
The arguments against the "genes-are-everything" paradigm are long and complex, but Cohen and Stewart also provide some simple, possibly simplistic observations supporting a much broader view of genetics.
- Mammalian DNA contains fewer bases than amphibian DNA, even though mammals are considered more complex and "advanced." The implication is that "DNA-as-a-message" must be a flawed metaphor.
- Wings have been invented at least four times by divergent classes (pterosaurs, insects, birds, bats); and it is very unlikely that there is a common DNA sequence that specifies how to manufacture a wing.
- The connections between the nerve cells comprising the human brain represent much more information than can possibly be encoded in human DNA.
- A caterpillar has the same DNA as the butterfly it eventually becomes. Ergo, something more than DNA must be involved. [This observation does seem simplistic, because DNA could, in principle, code for metamorphosis.]
Like DNA, this "something more" passing from parent to offspring conveys information on the biochemical level. This aspect of heredity has been by-passed as geneticists have focussed on the genes.
Cohen and Stewart summarize their views as follows:
"What we have been saying is that DNA space is not a map of creature space. There is no unique correspondence between the two spaces, no way to assign to each sequence in DNA space a unique animal that it "codes for." Biological development is a complicated transaction between the DNA "program" and its host organism, neither alone can construct a creature and neither alone holds all the secrets, not even implicitly."
(Cohen, Jack, and Stewart, Ian; "Our Genes Aren't Us," Discover, 15:78, April 1994.)
Comment. If "genes aren't us" the billion-dollar human genome project cannot fulfill its promises.