Geomagnetic Polarity Reversal: A Theoretical Modus Operandi of Punctuated Equilibrium Evolution
By Jay A. Yoder, Ph.D.
Department of Biology, The Illinois College, Jacksonville, IL 62650
Discontinuities in the fossil record provide the basis for the evolutionary theory of punctuated-equilibrium proposed by Eldredge and Gould (1972). Their theory suggests that the production of new species (as evidence of evolution) occurs by rapid bursts that are delineated by long periods (50,000 - 100,000 years in most cases) of stasis where no apparent changes take place. This contemporary theory of evolution, however, has not gained widespread acceptance and remains highly controversial (Futuyma 1986; Sober 1995). Clearly, to produce a significant evolutionary burst of this magnitude would require a most striking event leading to an abrupt change in gene frequency. Of the forces that are touted to alter gene frequency and drive evolution (inverse of Hardy-Weinberg Law assumptions; Griffiths 1996), none appear capable of generating such a dramatic alteration so quickly. Though genetic drift has been invoked to explain this anomaly, its impact, too, has been challenged (Futuyma 1986; Sober 1995). How evolution becomes 'punctuated' is puzzling.
One possibility could involve magnetic (polarity) reversal, a relatively rapid change in the polarity of Earth's geomagnetic field where the North Pole becomes the south magnetic pole and vice versa (Jacobs 1984). This theoretical force of evolution operates on Ecke et al.'s (1995) newly-discovered relationship between chiral symmetry (= handedness) and the orientation of the magnetic field; spiral defect patterns displaying distinct handedness form observed in a chaotic flow of carbon dioxide in a Rayleigh-Benard convection broke symmetry when the rotation about the vertical axis (spiral analog of the magnetic field) was reversed. These investigators concluded that the winding direction of a spiral was analogous to a magnetic spin. That is, a right-handed magnetic spin generates a clockwise spiral and a left-handed magnetic spin reverses the spiral counterclockwise.
With regard to DNA, a change in the orientation of the magnetic field would therefore translate into a left-handed (counterclockwise spiral) to right-hand (clockwise spiral) switch (Z-DNA to B-DNA that can now be transcribed) or the reverse (B-DNA to Z-DNA whose role may be involved with regulating expression of certain genes or in genetic recombination) (Lodish et al. 1995; Griffiths 1996). Such changes in handedness of DNA would lead to gene activation or deactivation (Lodish et al. 1995), differential gene expression, and a change in gene frequency that drives evolution. Most strikingly, as is well known to geologists, reversals in the orientation of the Earth's magnetic field occur every 10,000 - 100,000 years (Jacobs 1984) and thus, the pronounced bursts of speciation associated with punctuated-equilibrium evolution are reflected by abrupt changes in gene frequency as a result thereof.
My theory operates on the following premises:
1.) The DNA double-helix exists in both right-handed, clockwise spiral (B-DNA) and left-handed, counterclockwise spiral (Z-DNA, though only in short tracts) forms in prokaryotic and eukaryotic cells (Lodish et al. 1995; Griffiths 1996);
2.) Only B-DNA is transcribed, whereas Z-DNA is not (Lodish et al. 1995; Griffiths 1996);
3.) A change in magnetic field orientation affects chirality or handedness; the winding direction of a spiral is analogous to a magnetic spin (Ecke et al. 1995);
4.) Geomagnetic polarity reversals involve changes in the polarity of the Earth's magnetic field, where the North Pole becomes the south magnetic pole and vice versa (Jacobs 1984);
5.) Geomagnetic polarity reversals occur relatively rapidly (Jacobs 1984);
6.) A polarity reversal occurs every 10,000 - 100,000 years (Jacobs 1984);
and on the following assumptions:
1.) A switch in the handedness of DNA (Z to B or the reverse) is responsible for the differential gene expression and hence, changes in gene frequency (Hardy-Weinberg equilibrium is violated; evolution != 0) (Lodish et al. 1995; Griffiths 1996). Short Z-DNA tracts may play a role in the regulation of the expression of certain genes or in genetic recombination (Lodish et al. 1995; Griffiths 1996).
2.) The direction of winding (handedness) of DNA is influenced by the orientation of the magnetic field, an assumption taken from Ecke et al.'s (1995) observations. Thus, an inversion of B-polarity causes a change in the winding direction.
3.) Certain sequences of DNA are more labile ('electromagnetically vulnerable', thus more prone to reversal of spin) than others with regard to magnetism, otherwise, a magnetic reversal as described would lead to more dramatic changes in simply activating or deactivating genes. Massive species extinction may be expected if net Z-DNA switched to B-DNA, because the 'blue print' has been completely altered, not just modified. Thus, the entire genome does not reverse spin; a change from B-DNA to intranscribable Z-form would be lethal to all organisms.
In accordance with this theory, variations in timing between 'punctuated' peaks of speciation can be accounted for by such natural phenomena as (Jacobs 1984; Butler 1992):
1.) Short periods of constant geometric polarity, usually <10,000 years (geomagnetic events = geomagnetic excursions = polarity excursions); an interval of time where the geomagnetic field attempted unsuccessfully to reverse polarity;
2.) Periods of constant polarity of the geomagnetic field, usually >10,000 years (polarity epochs = polarity interval; the time interval is called a magnetic epoch).
Taken together, these considerations imply that the bursts of speciation associated with punctuated-equilibrium evolution derive from a simple handedness-switch from B-DNA to Z-DNA, or B to Z, in response to a relatively rapid reversal in the orientation in Earth's magnetic field. For the first time, this reveals that Earth's magnetic field is an important natural force of evolution.
Additionaly Considerations
Single-stranded DNA possessed by certain viruses, prokaryotes and protists is anticipated to react to magnetism in a like manner, because their DNA is probably twisted in some way due to the presence of chiral centers in nucleotides. Evolution would be expected to proceed slowly in organisms living in certain geographic 'islands' that are unaffected by shifts in magnetic field. Reversals in magnetic polarity as described may be more likely to produce a genesis instead of evolution; changing the 'handedness' of an organism's DNA may be expected to be completely intranscribable in many species, and, thereby yield many 'new' species. The fossil record would thus show many of the extinct species shortly after the magnetic reversal. Reversal times may correlate directly with bursts of speciation; alternatively, they may be out of sync.
As a final comment, proof that the magnetic field exerts an impact on gene expression has recently been demonstrated Rao and Henderson (1996) reported electromagnetic field sensitivity on regulation of the c-fos gene that encodes the Fos protein, an important nuclear transcription factor. Thus, there is a link between magnetic field and gene expression.
Author's note - The purpose of this article is to foster discussion, with the hope that it will lead to new research in this particular area.
Literature Cited
Butler RF. 1992. Paleomagnetism. Oxford; Blackwell Scientific Publications.
Ecke RE, Hu Y, Mainieri R, and Ahlers G. 1995. Excitation of spirals and chiral symmetry breaking in Rayleigh Benard Convection. Science 269:1704-1707.
Eldredge N, and Gould SJ. 1972. Punctuated equilibria: an alternative to phyletic gradualism. In TJM. Schopf (Ed.), Models in paleobiology San Francisco; Freeman, Cooper and Company pp. 82-115.
Futuyma DJ. 1986. Evolutionary Biology. Sunderland; Sinaur.
Griffiths AJF, Miller JH, Suzuki DT, Lewontin RC, and Gelbart WM. 1996. An introduction to Genetic Analysis. New York; WH. Freeman.
Jacobs JA. 1994. Reversals of the Earth's Magnetic Field. Bristol; Adam Hilger.
Lodish H, Baltimore D, Berk A, Zipursky SL, Matsudaira P, and Darnell J. 1995. Molecular Cell Biology. New York; WH. Freeman.
Rao S, and Henderson AS. Regulation of c-fos is affected by electromagnetic fields. Journal of Cellular Biochemistry. 1996. 63:358-365.
Sober E. Conceptual Issues in Evolutionary Biology. 1995. Cambridge; The MIT Press.
