Darwin and His Orchid

Source: John Tann via Conservation Jobs.

The story of the Angraecum sesquipedale, or ‘Darwin’s Orchid’ is a relatively obscure anecdote from the annals of natural history when juxtaposed with some of the more tumultuous debates and great discoveries of its time. Nevertheless, it’s a strikingly elegant example of a victory of Darwin and his cohort over their myriad critics and opponents. In the mid-nineteenth century, even before Darwin had become a household name, evolution was a hot topic in Victorian society. In 1844, Vestiges of the Natural History of Creation was published and was read not just in academic circles but across the wider educated public. Prince Albert purportedly read the entirety of Vestiges aloud to Queen Victoria in early 1845. It was against this backdrop that Darwin chose to publish his 1859 magnum opus On the Origin of Species.

Needless to say, some circles of society were hotly opposed to the new theory of natural selection put forward in On the Origin of Species.  The idea of the evolutionary origins of man was not necessarily new at the time – Darwin’s grandfather, Erasmus Darwin was himself an early evolutionist –but along with Darwin’s latest input it continued to be seen as a moral contradiction to Christianity’s literal creationist doctrine. Many liberal Anglicans supported the theory, seeing no opposition to their faith in Darwin’s words, However their enthusiasm was not at all shared in more conservative circles. David Livingstone, the Scottish missionary famous for his explorations of Africa claimed that he could see no “struggle for existence” (a phrase commonly used by Darwin and the title of the third chapter of On the Origin of Species, Darwin borrowed the phrase from the clergyman and political economist Thomas Malthus, who used it to describe the population trends among the poverty-stricken masses in East London) in the plains of Africa. The confrontation reached its heated climax one year after Darwin’s publication when the Bishop of Winchester, Samuel Wilberforce, faced Thomas Huxley (‘Darwin’s bulldog’) in the now famous Oxford debate, wherein Wilberforce is said to have asked Huxley: “Was it through your grandfather or grandmother that you have descended from an ape?” This was neither the first nor the last confrontation regarding evolutionary theory, with high profile debates continuing even today (one example of a famous case in the last century is the 1925 ‘Scopes Monkey Trial’).

During his career, Darwin had spent a large proportion of his time investigating the reproductive mechanisms of plants. In 1862, he published Fertilisation of Orchids, in which he discussed the co-evolution of orchids and insects. In the work, he detailed the Angraecum sesquipedale, a flower discovered in Madagascar just over half a century prior. Also called the ‘Star of Bethlehem’ orchid, the flower received the name due to the  distinctive shape of its petals. However, its most notable feature is its remarkably long spur (about 11 inches) at the bottom of which is its nectary. Darwin, having been sent several of these flowers earlier in the century, surmised that such a singular feature must indicate the existence of an insect with an accordingly long proboscis, the two species having co-evolved. He explained the details of his hypothesised evolutionary mechanism in Fertilisation of Orchids:

As certain moths of Madagascar became larger through natural selection in relation to their general conditions of life, either in the larval or mature state, or as the proboscis alone was lengthened to obtain honey from the Angræcum and other deep tubular flowers, those individual plants of the Angræcum which had the longest nectaries (and the nectary varies much in length in some Orchids), and which, consequently, compelled the moths to insert their probosces up to the very base, would be fertilised. These plants would yield most seed, and the seedlings would generally inherit longer nectaries; and so it would be in successive generations of the plant and moth. Thus it would appear that there has been a race in gaining length between the nectary of the Angraecum and the proboscis of certain moths; but the Angraecum has triumphed, for it flourishes and abounds in the forests of Madagascar, and still troubles each moth to insert its proboscis as far as possible in order to drain the last drop of nectar.

This idea was ridiculed by Darwin’s opponents such as the Duke of Argyll. He claimed that such a remarkable flower as the Angraecum sesquipedale clearly showed divine creation. For the Duke and many others, this blind evolutionary arms race was unnecessary. Clearly, the discovery of such an insect didn’t preclude the possibility of divine creation. Rather, it vindicated Darwin’s claims in the face of his fiercest critics, providing much needed evidence for his theorised co-evolution mechanism.

Sadly, Darwin did not live to see his bizarre moth discovered, but sure enough it was found in Madagascar in 1903, 21 years after his death. Upon verification, the large hawk moth was named Xanthopan morganii praedicta in honour of Darwin’s insight, and even today is renowned, along with its partner the A. sesquipedale, for the drama surrounding its postulated existence.