It’s a surprising fact, a fact that warns of overpopulation and a world teetering on the edge of exhaustion: The number of people alive today outnumber all those who have ever lived.
And it’s dead wrong. Ciara Curtin in the Scientific American does a nice dismantling of this urban legend.
Why did this falsehood spread? It has the snap of unexpectedness that you find in a lot of scientific-ish urban legends. (You only use 10% of your brain!) It balances that surprise factor by tapping into our sense of concern and anxiety for the world. (Have we pushed the planet too far?)
The surprise value and emotional resonance are garden-variety strengths of urban legends. This legend has another tricky feature, though. It appeals to our intuition about exponential numbers — for instance, if you take a sequence like 3^2, 3^3, 3^4, …, each successive number is greater than the sum of all the numbers before it in the sequence. If we have the (mistaken) sense that the earth’s population works like this sequence, the urban legend would seem quite reasonable. (It might even, perversely, make us feel smarter to believe it than not to believe it, since in tracing the exponential logic in our heads, we might flatter ourselves to believe we had solved the logic puzzle that explained a surprising “finding.”)
Here’s some real-world math to complement your post. From time to time we hear of so-and-so being a “…direct descendant of…” {pick any name from antiquity}. Say, Attila the Hun, King Solomon, or whoever. Holy Grail stories seem to have lots of these claims included – direct descendants of Jesus and Mary Magdalene, embedded in French royal lines etc..
For fun, using Carl Haub’s cited estimates of total population of 500M by 1650 A.D. as a target, what might the odds be for such a claim to be valid?
Well, taking an average parental age of 25 (reasonable) that means 4 generations per century, or about 32 generations in 800 years, so 2 parents, 4 grandparents expands dramatically, creating 2^32 ~= 4B slots on each of our ancestral trees by around 1200 A.D. Since we have less than 500M candidates to occupy the 4B slots, once we go back more than 700 years, the really special thing is not to be “descended from Attila” at all, but to NOT be. Beyond that point, every possible candidate gets to occupy multiple slots on the tree, via multiple pathways.
Given historical occurrences of invasions, migrations, pillage and rape, once enough time has passed, and that’s about a millenium or less, everyone who could be an ancestor is an ancestor, except in vanishingly small-likelihood cases of total abstinence, exclusively gay individuals, or lineage extinction within a few generations from massacres involving total ethnic cleansing (taking the women as slaves after a victory actually increases the mixing process rate).
So, if you want to have a worthy ancestral role model to live up to, pick your favorite historical character – you probably are his/her descendant. Just as long as you don’t mind sharing. Because our ancestors really are part of our shared heritage.
And if French and Scottish parties claim descent from Mary Magdalene, they’re probably right.
Thanks! Really interesting. I wish i could spend my time on writing articles…just have no time for it.
Good job.
Interesting indeed.