COMPUTING SCIENCE
Experimental Lamarckism
Brian Hayes
Looking for Lamarck in All the Wrong Places
If Lamarckism has no value in a static environment and only the
slimmest of marginal benefits in a fast-changing environment, it's
natural to wonder if there might be some intermediate condition
where the utility of Lamarckian inheritance is maximized. This would
be a condition where change is quick enough to make learning
worthwhile, but not so rapid as to make genetics irrelevant. I have
surveyed a broad range of rates of environmental variation looking
for this point of optimality, without reaching any firm conclusion.
The level of statistical fluctuations in the output of the model
suggests that much longer runs and larger populations would be
needed to settle the question. I do feel confident in saying there
is no level of variation where Lamarckian inheritance is worth as
much as learning is, or even half as much. But there may be a range
of variation rates where a species could benefit from a Lamarckian
mechanism if it cost no more than a tenth of what learning costs.
Even where the model's answers are clear, they are at best
preliminary and provisional. The model is too simple to capture much
detail about the lives of real organisms. On the other hand, it's
not simple enough to explore the entire space of parameter values.
Another reason for caution is that the model sometimes behaves in
ways I don't understand. For example, in certain mixed-population
experiments the Lamarckian gene is driven toward the lowest possible
values, indicating it is unfavorable and "wants" to be
zero, yet at the same time the Lamarckian breed drives its
competitors to extinction. What does that mean?
It would be interesting to test the model on problems other than
moth camouflage, especially problems where the environment is not a
passive background but can react and evolve on its own. One realm
where Lamarckian mechanisms look particularly attractive is the
immune system. Every child must reinvent immunity to measles and
chickenpox and other diseases. It's done through a miniature
Darwinian process of generating many random antibodies and selecting
those that recognize a pathogen. Wouldn't it be better to pass on
the selected antibody genes to later generations, so that babies
would be born pre-immunized? Edward J. Steele of the University of
Wollongong in Australia argues that something like this does go on
in the immune system, through the agency of reverse transcriptase.
But Steele has won few converts. It's hard to be a believer in
genetically transmitted immunity when your parents had chickenpox
and you had chickenpox and your children get chickenpox.
If Steele's mechanism could exist, would it prevent disease? The
obvious drawback is resistance: A generation born with a high titer
of antibody would exert powerful selective pressure on the pathogen,
so that mutants with slightly different surface markers would
proliferate. Thus every generation would have to come up with a new
defense anyway, and Lamarckian inheritance would be rendered
superfluous. But this is speculation; a model might well reveal
subtler effects.
In closing, I want to say a word about cultural evolution, which is
often described as a Lamarckian process. Suppose it were
truly Lamarckian: Suppose some neurogenetic innovation
allowed your children to be born already knowing everything you
know. What a boon to humanity! What a head start! No one would ever
again have to spend all those years learning the alphabet and the
multiplication tables and the conjugation of Latin verbs and the law
of cosines and the preamble to Evangeline and the date of
the Battle of Hastings and how to ride a bicycle. But the more items
I add to this list—let's not forget the state capitals or the
nine orders of angels or the 20 amino acids or the recipe for mom's
meatloaf—the more I'm struck by the fundamental problem of
Lamarckism. Which acquired traits do you choose to pass on?
© Brian Hayes
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