The History of Haldane's Rule 

was described by W. A. Craft (Quarterly Review of Biology (1938) 13, 19-39)in a paper entitled: 

The Sex Ratio in Mules and other Hybrid Mammals

"Buffon (1791) was one of the first to call attention to the proportion of the sexes in hybrids. He expressed the opinion that an excess of males occurred. Colonel Hamilton Smith (1841) stated, that it is observed in general that males are much more abundant than females in hybrids and that the fact is equally true in mules, where the males occur in the proportion of two or three to one female. Gadeau (1899) also stated, that the results of hybridization are much oftener males than females, and that male offspring are more numerous in proportion to the specific distance between the two parents. Suchetet (1897) expressed the opinion that in hybrid birds males are more numerous than females and cited numerous observers."

Thus there was much confusion about which sex decreased in different organisms until Haldane realized that it was always the heterogametic sex. In some organisms males are the heterogametic sex, and in others females are the heterogametic sex.

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This page was last edited 02 Feb 2004 by Donald Forsdyke