A somewhat bizarre and recurrent claim on some social media sites, is that the theory of evolution requires faith to believe in. Hence it’s analogous to a religion. (Often that prefaces an assertion that it requires an extraordinary amount of faith).

The theory of evolution however, doesn’t require faith or beliefs. It’s accepted in the scientific community (and in most secular countries, by a large chunk of the population) because of evidence.

We only need to establish four basic facts for evolution to be- at the very least- deductively correct.

First, it has to be the case that a population of organisms varies in their traits. This is readily observable. This variation is a necessary condition of evolution.

Second, there has to be a mechanism of inheritance. Again, this has been firmly established. Chromosomes carry DNA. DNA is the molecule of inheritance.

Third, selection[1] has to operate on populations or organisms. Again, this is observable. The example of the pepper moth is a classic example from the wild. Pesticide resistance in insects is another example.

So these three things means that evolution is going to occur. Evolution is about shifts in gene frequency. Some genes become more common, some genes become less common. So these facts mean that some traits will be selected for. They will have some evolutionary advantage. Mosquitoes that are resistant to common insecticides will be more successful than those without this resistance. These will pass this trait on to their descendants. And there will be a lot more resistant mosquitoes in the population as a result.

That leads to the last condition for evolution. That’s just time. There is a lot of time available. Early geologists pondering the rock stratas in Europe and North America deduced that Earth is very old. Biologists appreciating the slow, incremental nature of selection, deduced that the Earth is very old. And finally, Clair Patterson nailed the age of the earth down with a lot more precision when lead isotope analysis showed that the earth was 4.5 bn years old.

So, none of the above facts actually require any faith. Evolution is just a necessary consequence of these factors. Now in science, we also go a bit further than this. We also try to make predictions based on this. One very important area of prediction are fossils. The Theory of Evolution is going to make some pretty bold claims about the order in which fossils appear and the types of features these fossils will exhibit.

An excellent example of this is Tiktaalik roseae[2]. This is an important fossil that shows some of the transitional properties we expect between fish and tetrapods (the early vertebrates that first conquered land). From the theory of evolution there should be transitional forms in the late Devonian (375-363 Myr). Palaeontologists looked, and yes, we got it right. It’s there in the Late Devonian and its got dorsally mounted eyes and a neck and head capable of independent movement.

Image linked to National Geographic
[1] Selection isn’t the only mechanism of evolution. Other factors such as genetic drift or hybridisation also can play a role.
[2] Downs, J.P., Daeschler, E.B., Jenkins, F.A. & Shubin, N.H.(2008) The cranial endoskeleton of Tiktaalik rosae Nature 455: 925-929