The Price is always right!

I like to think that I am smart enough for what I do. I’ve published over 100 papers, supervised over 70 postgrads, lectured in topics from evolutionary biology, phylogenetics and taxonomy, to philosophy of biology. Obviously, there are lots of smarter people around me but I like to think that I can hold my own.

I can tell you about the subtle differences among multiple species concepts, the benefits of using Bayesian over maximum likelihood analyses, how to determine different types of penguin species, explain gene function in possums and so on.

One of the books in the inaccurately named Hitch-hiker’s Guide to the Galaxy trilogy, by the great Douglas Adams. The concepts in here can be tricky enough to parse… Image by Adrian Paterson

But…. There is one area of biology that makes me feel way less than smart. This is the Price Equation.

In the Hitchhiker’s Guide to the Galaxy, civilisation builds the biggest computer in the universe to find the answer to life, the universe and everything. The answer is 42. They then build a larger computer to find the question that they should have asked.

They could have just used the Price Equation.

The Price Equation answers everything in evolution (which is everything important in the universe). Or certainly everything about variation and change in traits over time, like gene change (which is everything important in evolution). It was developed by George Price in 1970 and was so novel that Price could not cite any other papers.

The Price Equation takes change in a trait and divides it into change driven by altered frequencies and change driven by altered measurements. In evolutionary biology this is equivalent to change from natural selection and change from transmission.

So far so good(?)….

Here be dragons…. or at least the Price Equation. Image by Adrian Paterson.

What does this mean? Here it gets a little more hazy. Jeremy Fox, a Price Equation fan, has an example using voting in subsequent elections (see the details here). Basically, comparing one election to the next, political parties want more votes. They can do this in two main ways, getting people who did not vote last time to vote in the next election (this is altering frequencies) and getting people who voted for the other party last time to change and vote for you (this is altering measurements or transmission).

Adding voters changes the frequency or proportion of who votes for you by adding a person and increasing the population. Changing a voter’s preference both adds a voter for you but also takes a vote away from the other party (but does not increase the population).

Ok, I think I understand. From an evolution perspective, this allows us to look at a change in a trait from one generation to the next, say an increase in size, and being able to say how much is from natural selection (those with genes for being larger survive better than those that don’t) and how much is from environmental, and other, factors (a cooler year may produce larger individuals).

The Price Equation can, ultimately, be used anywhere where there is a bunch of traits in a population that can be expressed as a function of frequencies and measurements. This has allowed it to be used in physics, economics, as well as population genetics.

Don’t ask me to explain the mathematics behind this….

The fearsome whiteboard of Will Godsoe, I dare not enter… Image by Adrian Paterson

Luckily, there is a big brain in the same building as me who really does understand the Price Equation. Will Godsoe loves the Price Equation. There is a standard joke about how long we will have in a conservation with Will before the Price Equation is mentioned (complete with a diversion to a whiteboard).

Talking to Will does not make me feel smart!

Will has published a couple of papers on making the use of the Price Equation. Will has published on applying the equation to biodiversity change. His most recent paper is on producing a generalised Price Equation that can be used in many more situations than it has been so far.

Obviously, there is a whole lot more to this but we are now reaching the outer reaches of my knowledge. It’s certainly nice knowing that something like the Price Equation exists and can start to unlock the secrets of evolution, the universe and everything.

But I might let others do the heavy lifting in this one.

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