978 Note
Monochiralities Caused by Sexuality Alfred Klemm
Max-Planck-Institut für Chemie (Otto-Hahn-Institut), Postfach 3060, D-55020 Mainz
Reprint request to Prof. A. K.; Fax: +49 6131 305388 Z. Naturforsch. 55a, 978 (2000);
received November 23, 2000
It is shown how the interaction of sexuality and chirality causes monochiralities of the biosphere.
Key words: Evolution; Sexuality; Chirality.
In [1], Rikken and Raupach say: "We show experimen- tally that magnetochiral anisotropy can give rise to an enan- tiomeric excess in a photochemical reaction driven by unpolarized light in a parallel magnetic field, which sug- gests that this effect may have played a role in the origin of the homochirality of life."* Also the fact that outside the tropics the sun goes always to the right (left) on the northern (southern) hemisphere suggests that this effect may, via the sun-dependent growth of organisms, have played a role in the origin of the homochirality of life.
Such effects which imply that the speed of the mono- chiralisation is proportional to the mole fraction of the not jet monochiralised organisms, lead very slowly to monochirality.
In [2] it was shown that the interplay of sexuality and chirality implies that the probability that a male and
[ 1 ] G. L. J. A. Rikken and E. Raupach, Nature 4 0 5 ,9 3 2 (2000).
[2] A. Klemm, Z. Naturforsch. 40a, 1231 (1985).
female organism with the rare chirality are fruitful is pro- portional to the square of their small mole fraction. This leads much faster to monochirality:
If in an isolated population there are male and female organisms which mate regardless of whether their chira- lities are equal or not, and whose copulations are only fruitful if their chiralities are equal, then the organisms with the less abundant chirality will finally die out becau- se their copulations are more often fruitless than the copu- lations of the organisms with the more abundant chirali- ty.
Even if in an isolated population right and left handed organisms are equally abundant and external influences can be neglected, with equal probability one of the chiralities will become dominant because such a system is, as to the chiralities, in an unstable equilibri- um.
If in the course of time such isolated monochiral popu- lations of different chiralities mix, then again the chira- lity of the greater population will survive.
Since the "invention" of sexuality, in this way mono- chiralities on earth were created without the necessity of any external influences.
An example is given by the land snail Partula sutural- is on the island Moorea near Tahity [3], on which there exist snails of different monochiralities of their shells in different isolated valleys. If by the experimenters such different monochiral populations are mixed, the chirali- ty of the greater population survives.
[3] cf. J. Murray and B. Clarke, Proc. Roy. Soc. London B211, 83 (1980).
* The homochirality of life consists of its various right and left monochiralities. The word chiral stemms from the Greek word X£iQ, meaning hand.
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