Baseball Cards and Evolution

A Sacred Chain Story

The third part of my new book (The Sacred Chain: How Understanding Evolution Leads to Deeper Faith) is called the Challenge of Species. We are hard-wired to think of things according to stable categories. And particularly when we think of the category we call “human beings”, it is pretty important to our theology to be able to determine which individual organisms properly belong to it, and which ones don’t: which individuals bear the image of God??

Today, it’s not so hard to make that determination. The next closest individual organisms are chimpanzees and bonobos, and no one mistakes these for us (though historically, when European explorers first saw them from a distance, they called them “primitive hairy men”). But if we go back in time on the human lineage, things get tricker.

That’s because evolution works in small, almost imperceptible increments in the short term. It takes a really long time to see significant changes, and there is not an easy dividing line for when one species turns into another. It isn’t right to say that someone’s parents or grandparents (or great great great grandparents) were a different species.

To try to show just how long we’re talking about, I’ve devised another thought experiment (that’s what philosophers do instead of doing actual experiments in laboratories): a stack of baseball cards. But instead of each card having a picture of a baseball player, imagine that they have a picture of one of your ancestors. And furthermore, let’s say that in the stack, each card goes back one generation. So in my stack of cards, I’m on the top one, then one of my parents is on the next one down, one of my grandparents on the one after that, and so on.

According to a family friend who dabbles in genealogy, the 35th card in my stack would have on it St. Olaf II, the patron saint and king of Norway back around the year 1000. (Don’t be too impressed with my royal lineage; almost all of us are descended from prominent people that long ago who did pretty well at passing on their genes!). In my case, that works out to an average of about 30 years per generation, but of course this will vary somewhat for others. Scientists commonly use 25 years as the average length of a generation for humans. These days women tend to give birth at later than 25 years old; they used to do so at a younger age. And men have typically been older than women when their children are born. But over long stretches of time, these numbers average out to around 25 years per generation.

I still have a collection of actual baseball cards from my youth, hoping they might fund my retirement one day (though at the moment it looks like I’ll have to work for another 100 years before they become valuable enough to do that). I pulled out a bunch of nice crisp ones and measured how many cards there are in a stack, and I found there to be exactly 50 cards in a one-inch stack. Using the average of 25 years per generation, a one-inch stack takes us almost back to the year 770 where Charlemagne would appear for anyone with European ancestry (our 47th-great grandfather).

Say your stack of baseball cards is now about 3.2 inches tall. You’re still on the top, your parents next, and so on. The bottom card of that stack might very well have the biblical Abraham on it. He probably lived around 2000 B.C., or 161 generations ago. A stack of 3.2 inches doesn’t seem that tall, but it already takes us way back into antiquity. But let’s keep going.

In another part of the book I describe how some of our species, Homo sapiens, started moving up into the Middle East and Europe from Africa about 50 thousand years ago. There they encountered Neanderthals whose ancestors had been living in reproductive isolation from us for several hundred thousand years. That much time gave rise to enough differences that most scientists today consider them a different species. But that’s just the blink of an eye in evolutionary time, and they were still compatible enough with Homo sapiens that they could interbreed. All of us today who have ancestry from Europe or Asia are 2-4% Neanderthal according to our DNA. That means around 2,000 generations ago, one of your 1997th great-grandparents was a Neanderthal. In our baseball card thought experiment, a Neanderthal appears 40 inches down in your ever-growing stack. 

What about the beginning of our species, Homo sapiens? There are fossils that were discovered in Morocco that are about 300 thousand years old and thought to be very near the beginning of our species. That equates to about 12 thousand generations, or a stack of baseball cards twenty feet high. That represents a lot of Homo sapiens that have lived on this planet — the vast majority long before Abraham (remember he is only 3.2 inches down on the stack).

I discuss the relationship between the terms “human” and “Homo sapiens” and note that there is not complete agreement on whether these mean exactly the same thing. There were 10 or 12 species in the past (that have been discovered so far) that are classified under the genus “Homo”. (Remember, classifications use Latin, and the Latin word homo means “man” as in our word homicide, the killing of another human, not the Greek word homo which means “same” as in our word homosexual.) If we go back to the beginning of Homo, that’s closer to 3 million years ago — ten times further back than our species’ origin. So there are 120,000 generations between us and them, and a stack of baseball cards 200 feet tall! Were all of these “humans” too? Did they bear the image of God??

What if we could trace our family tree all the way back to the last common ancestors we had with chimpanzees and bonobos? The estimates here start to get a bit fuzzier. In years, the split would have occurred about six or seven million years ago. The average length of a generation over this time was probably shorter than 25 years. Female chimps today can start having babies at about 14 years old, and males reach sexual maturity at about 16 years old. If we manipulate the assumptions a bit (though still well within the fuzzy values), we get some interesting numbers. Say the most recent common ancestor of humans and chimpanzees was 6.5 million years ago, and that the average generation over that time was 19.5 years. That gives us 333,333 generations — one-third of a million. And a stack of that many baseball cards is 555 feet tall, which is the height of the Washington Monument!

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I really like the image of a stack of baseball cards that high. It conveys just how far separated we are from our common ancestors with any other species living today. It’s a really, really long time to go back through all those generations. Using the numbers above, chimpanzees today are our 333,334th cousins (about 20,000 times removed because of their shorter generation time). These are not close enough relatives that you need to send them Christmas cards! 

Secondly, the stack of baseball cards shows us how gradual the changes are. Looking from one card to the next in that stack, you wouldn’t notice any substantial differences between successive generations. They might have different colored hair or other features different from their parents or kids — just like we do today — but you wouldn’t ever say that there was a species change between one card and the next. 

The cutoff for when a species changes over from one to the next during evolutionary history can’t be made at the level of individuals. We know that 500 thousand years ago there weren’t any Homo sapiens. But we know there were creatures living then who had babies, who had babies, who had babies, and so on, and that there are members of that ancestral line 100 thousand years ago who are rightly called Homo sapiens. There is no precise point at which one species turns into another.

I think that starts to answer the challenge of species that evolutionary science poses to Christian faith and whether we humans are really all that different than everything else. Next time I’ll write about the problem of whether we differ in kind from the rest of creation, or whether it is only a difference of degree.