Monday, 7 August 2017

From antelope placenta to the chi square distribution

The Four-horned Antelope (Tetracerus quadricornis)
Philip Sclater The Book of Antelopes 1894
Despite its appearance, this Indian species is not a true antelope, but belongs to the subfamily Bovinae. Its placenta was described in 1884 by Raphael Weldon then a Scholar of St John's College, Cambridge.
Gravid uterus of the Four-horned Antelope
Weldon Proc Zool Soc London 1884
There was a fetus in each horn and Weldon was struck by the relative paucity of placentomes (30 and 22, respectively).
One extremity of the chorion of the Four-horned Antelope
Weldon Proc Zool Soc London 1884 
Weldon thought the interplacentomal regions resembled the diffuse placenta of the pig. This may have been overinterpretation. There seem to be no subsequent descriptions of placentation in this species.
The Nilgai (Boselaphus tragocamelus)
Rufus46 (Wikimedia Commons) CC BY-SA 3.0
Together with the Nilgai, the Four-horned Antelope forms its own tribe. Benirschki examined a couple of Nilgai placentas (here). He did not find an unusual number of cotyledons but remarked they were not as neatly arranged in rows as in other species. So perhaps Weldon was on to something.

Raphael Weldon is not remembered for his placental research. He became a marine biologist and was professor of Zoology first at University College London then at Oxford. At UCL he collaborated with the mathematician Karl Pearson and founded the science of biometrics. Famously, he rolled a set of 12 dice no fewer than 26,306 times. The results showed a bias towards fives and sixes (more here). These data were used by Karl Pearson in the latter's seminal paper on the chi-square statistic.

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