490 i Flora Unveiled
to what they regarded as Sprengel’s materialistic interpretation of insect- mediated pollina-
tion as nothing more than an elaborate game of deception and exchange of services. He had
also referred to some insects as too “stupid” to navigate certain flowers and described insect
“larceny,” in which insects managed to steal nectar without performing pollination services
(see Chapter 15). Where was God’s wisdom in such an anarchic scenario?
Pollination by outside agents, such as wind or insects, was also bewildering because it
implied that outcrossing was the norm and selfing the exception. As we saw in Chapter
15, the hereditary material was widely thought to be a uniform essence. It was assumed
that selfing in hermaphroditic plants was nature’s mechanism to preserve the purity— and
thus the constancy— of the species by preventing the mixing of different species or variet-
ies. Outcrossing, on the other hand, would actually promote such mixing, leading to the
rapid dissolution of the species and universal chaos. Since species appeared to be constant
in nature, selfing ought to be the primary pathway. Thus, Koelreuter and Sprengel were
puzzled by the fact that most plants seemed to be outcrossers. As we have seen, Goethe had
pointedly excluded outcrossing from his theory of metamorphosis.
The idea that eighteenth- century naturalists would assume selfing to be more beneficial
than outcrossing may seem surprising today. Darwin observed the deleterious effects of self-
ing directly in his study of livestock breeding. Inbreeding, rather than contributing to the
constancy of a particular breed, promoted the appearance of “sports” among the progeny,
which differed markedly from the parental type. In contrast, the progeny of wild species
that were free to interbreed were generally true to type. Darwin became convinced that,
contrary to the conventional wisdom, cross- fertilization in nature actually stabilized spe-
cies, whereas inbreeding promoted their dissolution.
Darwin was able to demonstrate the beneficial effects of outcrossing in plants by carrying
out his own detailed cross- and self- pollination experiments in many different species and
families, which he published in 1876. Darwin summarized his findings as follows:
The first and most important of the conclusions which may be drawn from the obser-
vations given in this volume, is that cross- fertilisation is generally beneficial, and
self- fertilisation injurious. This is shown by the difference in height, weight, constitu-
tional vigour, and fertility of the offspring from crossed and self- fertilised flowers, and
in the number of seeds produced by the parent- plants.^18Applying this principle to the evolution of flowers, Darwin proposed a thought experi-
ment to illustrate how the nectar- secreting glands of flowers could have evolved through the
process of natural selection:
Now let us suppose that ... nectar was excreted from the inside of the flowers of a
certain number of plants of any species. Insects in seeking the nectar would get dusted
with pollen, and would often transport it from one flower to another. The flowers of
two distinct individuals of the same species would thus get crossed; and the act of
crossing, as can be fully proved, gives rise to vigorous seedlings which consequently
would have the best chance of flourishing and surviving. The plants which produced
the flowers with the largest glands or nectaries, excreting most nectar, would oftenest
be visited by insects, and would oftenest be crossed; and so in the long run would gain
the upper hand and form a local variety.