Two Baby Boomers Ask: How Many Other Generations?

We have long been fans of Dr. Henry Lewis Gates’ PBS program “Know your Roots.” Each week he welcomes several celebrities and researches their family trees. Let’s do some wildly speculative “science” today: based on that program. 

We all have parents, and grandparents. Then we have grandparents and great grandparents. Beyond that are 3rd and 4th grandparents. And so on, how far back does it go? Well, paleontologists have estimated that life goes back a full 3 ½ billion years and, quite possibly, a lot longer than that.  It’s been one generation after another all that time. How many generations are that? That’s where we get to that “wildly speculative” part. The two of us wondered if we could come up with an estimate.

How on earth could we possibly do that? Well, at least the first two billion years of life consisted solely of bacteria. How long is a bacterium generation? We turned to that modern fountain of human knowledge. Yep, our cellphone. We went to the search app and asked. It told us that most bacteria reproduce by splitting into two daughter cells about one time per day.  Then our cellphone multiplied 365 by 2 billion and said that this was exactly 730 million generations. That’s a lot!

Well evolution proceeded to produce the next and higher category of life: single-cell animal-like creatures called protozoa. They may have appeared as early as 1 ½ billion years ago and were the most advanced forms of life for the next 940 million years ago. Protozoans live longer than bacteria. Their generations run from a day up to a few months. Let’s guess and call them one month each on average. So that’s 940 million years multiplied by 12; that’s a bit more than 11 billion generations. Now we are up to over 740 billion generations.

After the protozoans things slowed down and got far more complex. The simplest invertebrate animals turn up in the fossil record at perhaps about 560 million years. Their generation times are very diverse. Our cellphone tells us that they commonly range up to a few weeks. Let’s accept an average of about two weeks, that’s 26 generations per year. It was another 30 million years before fish appeared so let’s “guesstimate” that at least another 780 million generations of invertebrates passed by.

The earliest vertebrate animals - the fish - were alone at the top of evolutionary tree for about 165 million years. Their generation times vary widely but our cellphone suggested that 3 ½ years might be near the average. That gives us another 47 million generations; we are now up to over 742 billion, but things were really slowing down a lot.

Amphibian generations are about five years. Today’s reptiles - lizards, snakes, tortoises - have generation times that range from 6 to 26 years. It’s much harder to estimate the extinct forms, but let’s use 15 years as an average for the reptiles. Surprisingly, it isn’t any longer for most mammals, ranging from weeks to several decades. Let’s go with an estimate of 15 years for the vertebrates. As a group, they show up about 310 million years and so we can calculate that we have seen a mere 20,666 million generations of them.

When you add it all up you get something a little more than 742,000,000                                                                            generations of living creatures, almost all of them being bacteria. We hate to use the tiresome word “awesome,” but what other word works here?

We are not aware that anybody else has attempted to do this sort of computation so this column may be original science – lets’ call it “science -” right here in the Mountain Eagle. Is this a great newspaper or what? But don’t take us too seriously. This has hardly been a peer review study. We have just done a quick and almost goofy estimate. Still, one thing does stand out. The passage of life on our planet has brought along an astronomically immense number of generations of living creatures. We think and we hope that we have brought you an accurate sense of that. We think you should know about this.

Contact the authors at randjtitus@prodigy.net. Join their facebook page “The Catskill Geologist.” Read their blogs at “thecatskillgeologist.com.”