310 
GENETICS: D. F. JONES 
Yet while this is true, the platforms in Fiji are post-Pleistocene in their 
development. The writer was unable to discover any evidence of 
Pleistocene wave-cut platforms. 
' Woolnough, W. G., Sydney, Proc. Linn. Soc. N. 5. Wales, 32, 1907 (431-474). 
2 Guppy, H. B., Observations of a Naturalist in the Pacific, vol. 1, Macmillan, 1903. 
3 Gerland, G., Beitr. Geophys., Leipzig, 2, 1895, (56). 
''Daly, R. A., Boston, Proc. Am. Acad. Arts Sci., 51, 1915, (157-251), p. 232. 
^Vaughan, T. W., Washington, J. Acad. Sci., 6, 1916, (53-66). 
DOMINANCE OF LINKED FACTORS AS A MEANS OF 
ACCOUNTING FOR HETEROSIS 
By Donald F. Jones 
BUSSEY INSTITUTION. HARVARD UNIVERSITYi 
Communicated by W. M. Wheeler, February 26, 1917 
The increase of growth derived from crossing in both animals and 
plants, which has been called heterosis, and the converse fact of decreased 
vigor resulting from inbreeding have been known for a long time but 
have never been satisfactorily accounted for. 
The investigations of East,^ G. H. ShulP and Hayes^ show that in- 
breeding does not result in a continuous degeneration but that the ef- 
fects of inbreeding gradually become less as complete homozygosis is 
approached and for all practical purposes finally become constant. Un- 
like strains are isolated which differ in the amount of growth they pro- 
duce. In many species these homozygous strains are always less vigor- 
ous than either parent. The decrease in vigor due to inbreeding has 
been shown to be correlated approximately with the decrease in the 
number of heterozygous factors present but without showing why there 
should be such a relation. It was simply stated that "greater develop- 
mental energy is evolved when the mate to an allelomorphic pair is 
lacking than when both are present in the zygote."* 
The conception of dominance as proposed by Keeble and Pellew^ 
as a means of accounting for these facts has had two serious objections. 
If heterosis were due to dominance of characters it was thought possible 
to recombine in generations subsequent to the F2 all of the dominant 
characters in some individuals and all the recessive characters in others 
in a homozygous condition. Such homozygous individuals could not 
be changed by inbreeding. Moreover, if dominance were concerned it 
was considered that the F2 would have an asymmetrical distribution. 
Both of the above objections to dominance have failed to take into 
consideration the facts of linkage. If the factors which govern an or- 
ganism's development are distributed in all the chromosomes and passed 
