Science Buddies: "Ask an Expert"

Hello,
I am conducting research on which primates humans are most closely related to. It is the Science Buddies project entitled "Neanderthals, Orangutans, Lemurs, & You—It's a Primate Family Reunion!". I have finished the project but I have one question. In procedure step 18b, it asks me to "Calculate the average mutation rate.". How do I do this?
Thank you for your feedback.
-Dominick

Hi Dominick,

You are doing a really interesting project about human evolution! (https://www.sciencebuddies.org/science- ... p019.shtml)

Here is the part of the procedure you're doing:
18. Calculate the rate of mutation for NADH5 in the primate line.
a. Divide the percent difference by millions of years ago for the time in the past at which the lineages split.
b. Calculate the average mutation rate.

When you divide the percent difference by the number of years that have passed since the lineages split, you are calculating the mutation rate for each lineage (in part a). Technically, that is an average mutation rate by itself, because mutation is not usually constant over time.

Once you have the mutation rate for each of the lineages, you could calculate an average for all the lineages combined. Just add the individual mutation rates and divide the total by the number of comparisons.

I hope that helps. Please post again (in this same thread) if you have more questions.

Heather

Hello again,
Thank you so much for your reply! I really appreciate it and now I understand that aspect of my project. However, I have another question. At what point do humans split from other species? From what I understand, humans were part of the same species as primates (such as chimpanzees, gorillas, etc.). That can be traced back to our common ancestor, which split into the many species of primates that exist today. If I was wrong in any of this information, please feel free to correct me. Thank you for your help.
-Dominick

Hi Dominick,

According to the procedure for your project, you will use the times described in Richard Dawkins' book, The Ancestor's Tale:
Neanderthal: 0.4 mya
Chimpanzee: 6 mya
Gorillas: 7 mya
Orangutans: 14 mya
Gibbons: 18 mya
Colobus monkeys, macaques, etc: 25 mya
Lemurs, tarsiers, etc, 63 mya

Each of these time points describes the time (in millions of years ago) that we think that group split from what would eventually become humans. In other words, that is the time we think the last common ancestor between humans and that group existed.

Remember that we are talking about a common ancestor and not anything looking like a modern human. But those times should allow you to do your calculations.

Heather