ASCAP April 1993, Vol 6, No 4, p 8-11
Reply to Dan Wilson
I really appreciated Dan Wilson taking up the
issue of genetic variation and frequency dependent selection (FDS) in the
January ASCAP. It is good to get some
dialogue going, rather than have one's contribution disappear into nothingness
like a splashless pebble into a pond.
We are
not really interested in positive FDS (when the fitness of a phenotype
increases with its frequency) because this just reduces variation. But we are very interested in negative FDS
(when the fitness of a phenotype is inversely proportional to its frequency),
because this can cause variation and even bimodality in a trait. So, I will use the term FDS, meaning negative
FDS.
We
might try making a list of instances of FDS, one could
always give up if it got too long. And
subdivided according to whether the instance might be relevant to ASCAP. Among the irrelevant instances, priority
would probably go to those concerned with predator avoidance, such as mimetic
morphs in butterflies; lizards who
"break" up or down a rock when a bird swoops; I expect that book on predator-avoiding
strategies called Protean Behaviour gives lots of examples. What about fish which turn left when the rest
of the shoal turns right? That would
probably depend on whether the predator fish was geared to eating a single fish
or a whole school.
Thinking of relevant possibilities, what about habitat selection? Is it more advantageous to select a fringe
habitat when everyone else is crowding into the fertile valley; or a mountain
habitat, when everyone else is in the plain?
Is this sort of thing maintaining the variation along John Birtchnell's
closeness/distance dimension (or along the introversion/extraversion dimension,
whose basis is thought to be highly genetic)?
And would it pay to be attracted to fishing when everyone else is mad on
hunting? The same would apply to food
preferences.
As you
know I think the most relevant examples to psychiatry are the alternative
competitive strategies, basically Maynard Smith's Hawk and Dove, which
translate into escalating and de-escalating strategies or even into high
self-esteem and low self-esteem strategies (both temporary as in mood change
and lifelong as in personality variants along the "vertical
dimension").
Then
there are alternative strategies for dealing with adverse climate. Consider species in which a proportion of the
population migrates or hibernates, while the remainder of the population stays
at home or above ground. It must be the case that the larger the proportion which migrates or hibernates, the more it pays
any one individual to try to battle through the winter fully awake on its
original territory (and, of course, vice versa).
What
about mating strategies? Does it pay
more to be monogamous when everyone else is promiscuous? Does it pay to fancy redheads when the crowd
prefers blondes (this would be the opposite of Fisher's runaway sexual
selection)?
These
examples can be seen against a background of those probably more numerous cases
in which it pays to do the same as everybody else. I am sure we as human beings have a tendency
to check all the time to make sure we are going along with everyone else, and
not only in clothes. I can remember a
patient who worked in a factory and lived about an average distance from
it. Every morning he would walk or cycle
to work "with the throng".
Then he retired and got a morning job in the opposite direction to the
factory. He had to go to work every
morning "against the throng".
He found this very stressful, it made him feel
out of step with his community. I am not
saying that is why he got depressed, but it can't have helped.
In
these cases, the payoff is maximal in the middle, and gets less as you approach
the extremes; the
result is reduced variation unless the variation is "fixed" by
heterozygote advantage. If for any
reason, it pays to be nearer one extreme, you get normal directional selection; if it pays to be
nearer either extreme, regardless of which, you get an increase in variation
until you get bimodality and can then speak of alternative strategies and FDS.
I was
amazed recently to read about alternative mammalian mothering strategies
(1). Apparently some rabbit mothers keep
their litter in a separate nest, which they only visit once every 24
hours. And tree-shrews are even more
extreme, only visiting their young once in 48 hours. Are they good or bad mothers? Certainly, John Bowlby might raise an eyebrow
at them. And what about captive rabbits who are forced to share a cage with their litter - is this
stressful for them? Do they get raised
HPA activity?
The
function of this apparent neglect is thought to be the avoidance of predators,
in that the predator finds it easier to locate the young when the mother is in
the nest, or when the mother is going to or from the nest. I am not absolutely sure whether this
variation in mothering occurs within species or only between species. Russ, what sort of gene, or protein, could
keep a mother from her offspring for forty eight hours at a stretch? (I imagine the genetic basis of the variation
has not been worked out, if it occurs within species, or the authors would have
said; it could
be a single gene, or polygenic with a threshold).
The
nest-with/nest-apart variation does not seem to be so obviously frequency
dependent as the migration/stay-at-home options. It is difficult to see how predators could
become skilled in detecting nests with or without mothers preferentially. It seems more likely that just directional
selection has been occurring for this mothering behaviour, and that is why the
variation has not been retained within species, if in fact that is the case.
*******************
Regarding the distinction made recently in ASCAP between those who look
at woods, trees and leaves, I am a leaf man myself. I would like to have discovered chlorophyll,
or the fact that some leaves fall off in winter when others don't. Likewise with diagnoses.
I would rather get the MRI people to examine a population of soloists after
receiving standing ovations, and compare them with a population who have
received cat-calls, and get to grips with the physiology of receiving boosting
signals (anathesis, but I have rather given up trying to get people to use this
terminology) and putting-down (catathetic) signals. It already seems likely from Michael
McGuire's work that the applauded soloists would have high platelet 5HT, and from a lot of studies that the booed ones would
have high blood cortisol (assuming hedonic anathetic signals evolved from
agonic anathetic signals [submissive signals] and the same for the hedonic
catathetic signal of booing). What and
where is going on in the brain? I think
the biggest difference would be found in Roman generals having a triumph
through the streets of Rome, but even in Roman times that (e.g., the
venepuncture) might have been hard to set up.
What
was the physiological status of that tribal elder (reported somewhere in the
anthropological literature) who farted during a solemn ceremony, got up and
went and committed suicide by impaling himself through the anus onto the top of
a pointed tree? He did not even receive catathesis, he only anticipated it (or got it from an
internalised other). Back to trees, you
see, it pays to stick to the point.
A
final thought. We know there are two
major dimensions of variation in human behaviour: extraversion/introversion and
neuroticism/stability. How is this
variation maintained? The two main
possibilities are heterozygote advantage (at one or many gene loci) and
frequency dependent selection (also at one or many loci). How can we tell the difference between
them? I think for this problem we need a
mathematical expert like Lindon Eaves, who when I was working in genetics was
trying to detect directional selection for extraversion, and his equations were
something else. I think it is true to
say that heterosis predicts unimodality whereas frequency dependent selection
predicts bimodality of the distribution of some underlying trait. People think you only get bimodality with
single genes, but you also get it with FDS, even when the genetic basis is
polygenic. The possibility of FDS makes
it worth looking for bimodality even in a trait which seems sure to be polygenic.
It is
sometimes said that the nineteenth century novelists were the first
psychologists, forerunners of Wundt, and able to deal with more fundamental
issues than Wundt was able to in his laboratory. Thackeray gave an interesting adumbration of
Maynard Smith's Hawk and Dove strategies in The History of Henry Esmond
(1852, Penguin, 1970, p 435):
'Tis nature hath fashioned some for
ambition and dominion, as it hath formed others for obedience and gentle
submission. The leopard follows his
nature as the lamb does, and acts after leopard law; she can neither help her beauty, nor her
courage, nor her cruelty; not a single
spot on her shining coat; nor the
conquering spirit which impels her; nor
the shot which brings her down.
(Re Beatrix Esmond's
proud reaction to the Duke of Hamilton's death just before their wedding.)
A similar view was expressed by Henry Kissinger
in The Necessity for Choice:
The real distinction is between those who
adapt their purposes to reality and those who seek to mould reality in the
light of their purposes.
I have a similar quote by Philip Roth on my
file in
Manning, A. and Dawkins, M.S. (1992) Animal
Behaviour 4th Edition.