![]() ![]() Phylogenetic trees help us make sense of the world. Obviously, this would be really useful information for someone who is putting together a family tree for related species (called a phylogenetic tree), but scientists can use this information for more than just planning really epic family reunions. The molecular clock basically measures the amount of time since two species have diverged from each other. How do scientists use the molecular clock? But at its essence, it’s just measuring the passage of time by using the mutation rate as a yardstick. You can’t use it to measure distance (or time) any more.īecause of this limitation (and others), there is actually a lot of science and math that goes on behind the scenes of a lot of these calculations. If the genes go through periods where they change very quickly and then don’t change at all, then it’s like having a yardstick with random ticks on it. You need to assume that the genes mutate at the same rate. This approach doesn’t come without limitations, though. ![]() If we divide the number of mutations by the mutation rate (5,000 mutations ÷ 0.001 mutation/year), we find out that these two turkey species are about 5 million years old. We also know the mutation rate: the species will show 1,000 new mutations every million years, or 0.001 mutation/year. Let’s say we analyze the DNA of the two species and find that there are 5,000 mutations that are different between them. We’re given the job of trying to figure out how different turkeys are related to each other, and there are two species-the Ocellated Turkey ( Meleagris ocellata) and the Wild Turkey ( Meleagris gallopavo). Let’s pretend that we’re taxonomists-biologists who study how organisms are related to each other. To show how this works, let’s take a simple hypothetical example. Measuring the age of a species with the molecular clock technique requires just two simple things: an estimate of the number of genetic mutations between a species and its closest relative and the average genetic mutation rate (i.e., how many mutations show up in a population in a specified time frame, such as 5 mutations per year). This technique is called the molecular clock, and it was thought up by scientists Linus Pauling and Emile Zuckerkandl in 1962. Scientists make a few measurements and plug the numbers into an equation to get an estimate of a species’ age. But the molecular clock can help make some estimates. You read and hear it all the time-“this is an ancient, million-year-old species,” or, “this animal has been around for hundreds of thousands of years.” But, how do scientists really know how old these species are? It’s not like they can use a time machine to see-not yet, at least. ![]()
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