Linnaeus and the evolution

Carl von Linnaeus 1707–1778

In Linnaeus’ time the view on nature was different from today's view. It was supposed that all species on earth were the same as on the day God created them, the same number and the same appearance. To study biology was to study the creation. God had not created chaos, but there was a system in the nature for man to discover.

Linnaeus saw it as his task to search for the system in nature. He had found a pattern for sorting the plants – the sexual system. In the beginning all species seemed to be easily arranged into his system, so Linnaeus believed that he had found the divine order in nature.

One day Linnaeus encountered a problem in the shape of a strange plant. It was almost identical to common toadflax, Linaria vulgaris, but it had a differently built flower. For this reason it had to go to another class than the common toadflax in the sexual system. He called the plant Peloria, which is Latin for monster.

Charles Darwin 1809–1882

Since Peloria did not fit into the sexual system Linnaeus tried to find a solution to the problem. In the end he had to approach the thought that the odd plant might be an example of a species that had originated from nature. When he wrote about this he immediately received a letter from a clergyman who warned him for such a dangerous thought. This happened more than 100 years before Darwin presented his ideas about the origin of species.

Linnaeus never wrote about his thoughts again but planted Peloria by the doorstep to his summerhouse in Hammarby. There he could sit in the summer evenings, smoke his pipe and meditate over this strange monster in God's creation.

Peloria – a monster

Peloria is a mutation of the common toadflax.

Common toadflax, Linaria vulgaris, has a two-lipped flower with a spur. It has four stamens, of which two are longer than the other two. It was hence placed in the class Didynamia in the sexual system. The Peloria flower on the other hand has five spurs and five stamens of equal length, and was placed in a different class, the Pentandria.

How could the stamens differ so much between two otherwise very similar plants? Linnaeus at last suggested that Peloria was a hybrid between common toadflax and some other, unknown, plant. If the seeds of this hybrid could germinate and grow into new Peloria-plants one would have had to draw the conclusion that new species could originate in nature.

Today we know that Peloria is a form of common toadflax, which every now and then appears by spontaneous mutation. Meeting Peloria Linnaeus had to consider that a species might not be as stable as he had thought.

Linnaeus’ thoughts about speciation through hybridisation were not erroneous; on the contrary he was much before his time in thinking like this. Speciation can happen when a hybrid goes through a duplication of its genetic material. With a double amount of genetic material, neither the hybrid nor its progeny can interbreed with any of the parental species. They are isolated and a new species has sprung up.

Spur: A spur is a conical part of a petal, often containing nectar. A visiting insect has to stick its proboscis into the spur to suck the nectar.

Mutation: A mutation is an instantaneous change in the genetic material. This can happen in many ways, for example under the influence of the strong UV-light of the sun. Some such changes are invisible while others can bee seen clearly. An example of a sometimes occurring mutation is the white flowered form of the otherwise blue flowered liverleaf, where the ability to produce blue flowers has been affected.

Last modified: 2021-11-25