Saturday, August 17, 2019

Darwin: Victorian Menage A Trois

In 1864, a few years after the publication of the Origin of Species, Darwin, fighting a bout of illness took up some botanical work on Lythrum, a genus of flowering plants known as loosestrifes. He had been breeding them on and off for many years. His interest was in their sexuality as they gave him a deeper understanding on the evolution of sterility and reproductive isolation. His theory of population divergence and the origin of new species depended upon the evolution of traits that prevented individuals and populations from mating with each other.

Lythrum was known for its triple sexuality. There were three kinds of flowers. The female stigma could be tall, medium or short-styled. Each was accompanied by two sets of male stamens.  If the female was tall, the males were short or medium sized.

Darwin realized through his breeding experiments that greater the difference in height between these sexual organs, the greater the frequency of sterility. Mating between the unequal sized sexes in the same plant produced sterile seeds.  This was evolution preventing inbreeding and favoring cross pollination.

Adrian Desmond and James Moore in their biography, Darwin: The Life of a Tormented Evolutionist, write about Darwin's mischievous side:

" Talk about illegitimacy might have shocked the ladies guilds, at least coming from Erasmus Darwin's grandson. (Grandfather's own bastardizing experiments were still supplying tittle-tattle. At this moment Darwin suspected the widow of a botanical friend, Francis Boott, to be an illegitimate granddaughter of old Erasmus). But Darwin was stolid, methodical, reducing the love of the plants to cold, clinical calculation. Sterile seeds counts somehow fitted an unromantic, data-crunching age. Not for him Erasmus's flowery personifications, as styles and stamens bent to embrace in a kiss:

Two knights before thy fragrant altar bend,
Adored Mellissa! and two squires attend.

Still, he could tease. Solicited by a Mrs Becker for something edifying for her ladies' literary society, he posted 'On the Sexual Relations of the Three Forms of Lythrum salicaria'. Goodness knows how many red faces left after hearing that 'nature has ordained a most complex marriage-arrangement, namely a triple union between three hermaphrodites,- each hermaphrodite being in its female organ quite distinct from the other two hermaphrodites and partially distinct in its male organs, and each furnished with two sets of males' ".

There is no doubt that Darwin was an outstanding thinker. But he also was a hands on guy. His thinking was not vacuous or overly speculative.  He was a tinkerer and putterer.  He produced data. By cross breeding plants. By dissecting barnacles. By co-opting pigeon breeders and noting down the variation in the size and shapes of different breeds. Documenting tiny differences between individuals within groups was crucial to his case that complex structures could evolve by incremental changes over generations.

From life's little details he built the grandest theory of all.

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