November 24 1859 marks the date that Darwin published the Origin of the Species. As a student, I don’t think you ever appreciate just what a brilliant piece of scientific work this was. It’s all diluted down and given to you in textbook summaries. And it always seemed so obvious. It’s only by reading the the Origin of the Species that you come to appreciate what an achievement it was.

Consider the basic argument for natural selection-
* Organisms have lots of offspring, most of which don’t survive
* Offspring manifest variations, some of which assist survival
* Assuming there is a mechanism for passing these good variations along, these will be selected for and become more frequent.
* Given enough time, new species emerge

The really clever thing here, is that there was no known mechanism to pass on successful traits when Darwin wrote this. There wasn’t any modern genetic theory lying around, waiting to be used. There wasn’t even really a rudimentary theory. Darwin effectively used the observations he made about the natural world to make a tacit prediction. There must be a means by which successful traits get passed on.

This remarkable scientific insight anticipated the modern genetics (1930s). It’s an insight that had to come out of knowing absolutely nothing about genetics and the mechanisms of inheritance. How did Darwin get it right? Essentially, by accumulating lots of evidence that could drive this insight.

He also made the correct inference on how old the Earth was. Again, this is a function of just seeing the world all around him. And initially, physics thought Darwin was wrong. Lord Kelvin calculated the age of the earth based on its temperature and came up with a figure much smaller than Darwin envisaged. In the end, Darwin was proved right. The answer lay not in Kelvin’s calculations, but his ignorance of radioactive elements. These create hotspots in the earth’s crust, changing the earth’s temperature dynamics completely.

Again, as a student you never really appreciate the brilliance contained in this book. Imagine just looking at a bunch of Galapagos Finches and going, you know, that must mean that modern genetics is just around the corner, and the Earth must be a heck of a lot older than we think. And being right.

What made Darwin’s book so compelling? It was not just the logic of the argument above. It was the catalogue of evidence accumulated over decades presented in the book, that helped convince many. It wasn’t just the finches, but decades of work, patiently gathering information.

Despite popular belief, Darwin didn’t overthrow the creationist model of biology. This had been gradually abandoned by many natural scientists already. The evidence of a loving, God who designed wildlife to fit their environment, was just not around to found. The evidence of mass extinctions in the fossil record, implied a far crueler and more capricious God than that of the bible. And the principle of design had taken a large knock when European animals were released into places like Australia. Rather than Australian animals being superbly designed for that niche, many such natives succumbed to the invasive species brought by people.

What Darwin did was to provide a mechanism on how organisms speciate. But natural selection was not the only contribution of the Origin. Sexual selection is another important mechanism. Male forms of some species have an appearance that is linked to partner preference. One of these examples is with NZ Harvestmen (or Opilionids). We actually have some polymorphic species.

NZ Stout-Legged Harvestman

Males can have two forms, not one. Why? One has very elaborate and outsized pedipalps. Hunting success is hindered, but females prefer to mate with such forms. The other form is more like the females. This form is a more successful hunter, but a less successful mater. There is a lovely, evolutionary equilibrium between these two forces that actually allows both forms to persist. One’s a more successful hunter, one’s a more successful suitor.

There are few scientific books that have ever had quite the same effect on the world as the Origin of the Species. It has gone on to influence our thinking about genetics and the mechanisms of inheritance, it drives conservation efforts, it underpins ecology, it influences human biology and behaviour and hence medicine. So, it is worth remembering on its 150th anniversary.