2016

Great-Great-200-Million-Times-Great Grandmother Fish

Great Great Grandmothers of Deep Time

How long is 400 million years? How do you get a child to understand that Grandmother Fish lived 400 million years ago? Honestly, that span of time is beyond the comprehension of an adult, let alone a child. So here’s a thought experiment to help little minds and big one appreciate the mind-boggling span of time between the first jawed fish and us. How long would it take you to say Grandmother Fish’s name if you said it out in full with all the “greats” that she deserves? It’s been 200 million generations since Grandmother Fish was alive, so she is our great grandmother with 200 million “greats”. If you said two “greats” per second, it would take you three years to say her full name.

Kids can understand what three years means. They might have siblings that are three years older or younger. They might remember how little they were three years ago, and they might imagine how old they will be in three years. It’s still a long time for a little mind, but it is comprehensible in a way that 400 million years is not. If you really want to drive this home with a kid, have them imagine that somewhere there’s another kid who is just now starting to say Grandmother Fish’s name with all the greats. Then for the next three years, occasionally remind your child that this imaginary kid is still saying Grandmother Fish’s name without a break. Poor kid. You can see why I call her just “Grandmother” Fish. Then three years after you first mentioned it, tell your now-older child that the imaginary kid has finally finished saying Grandmother Fish’s name.

The other value of this exercise is that it drives home an astounding fact. If you went back in time 400 million years and found the earliest jawed fish, they would be the direct-line ancestors of every human on the planet. They would literally be your flesh-and-blood ancestors, your family. The fish you found would also be the ancestors of all land vertebrates, not to mention nearly all fish. What a difference 200 million generations can make!

Here are all five Grandmothers, the number of “greats” in their names, and how long it would take to say the name out lout (at two “greats” per second). These figures are based on estimates from The Ancestor’s Tale by Richard Dawkins, a book that helped me greatly as I worked on Grandmother Fish.

• Grandmother Fish, the earliest jawed fish. 200 million greats. 3 years.
• Grandmother Reptile, the earliest amniotes. 170 million greats. 2.5 years.
• Grandmother Mammal, the earliest eutherians. 120 million greats. 2 years.
• Grandmother Ape, the earliest apes. 1 million greats. 6 days.
• Grandmother Human, the earliest behaviorally modern humans. 4,000 greats. 80 minutes.

The time it takes to say a name corresponds to the number of generations that have passed, not the number of years. Apes have a slower life cycle than our earlier ancestors, so the number of “greats” in Grandmother Ape’s name is relatively small compared to the 30 million years since she lived. 

And if a kid gets excited and wants to try saying one of these names out loud, let them try. See how far they get.