One-in-70-Trillion: An Evolutionary Biologist Explains the Mind-Bending Probability of Our Existence

At a 1998 con­fer­ence on tech­nol­o­gy and life, The Hitch­hik­er’s Guide to the Galaxy author Dou­glas Adams once pro­posed the notion of a sen­tient pud­dle. Imag­ine it “wak­ing up one morn­ing and think­ing, ‘This is an inter­est­ing world I find myself in — an inter­est­ing hole I find myself in — fits me rather neat­ly, does­n’t it? In fact, it fits me stag­ger­ing­ly well, must have been made to have me in it!’ ” No mat­ter how much intel­li­gence it may some­how have attained, this pud­dle does­n’t real­ize that its shape was dic­tat­ed by its envi­ron­ment, not the oth­er way around. Nor does it seem to real­ize on just how many fac­tors its very exis­tence is con­tin­gent; to its mind, this is a pud­dle’s world, and the rest of us are just liv­ing in it.

Of course, the rest of us are in just the same sit­u­a­tion. In the 70-minute Big Think video above, evo­lu­tion­ary devel­op­men­tal biol­o­gist Sean B. Car­roll puts our pres­ence on Earth in per­spec­tive, begin­ning with the var­i­ous fac­tors that hap­pened to con­verge to make com­plex life pos­si­ble on this plan­et at all. “A huge num­ber of things had to go right for our species to exist, and for each of us indi­vid­u­al­ly to exist,” he says, and that’s true on “the cos­mo­log­i­cal scale, the geo­log­i­cal scale, and the bio­log­i­cal scale.”

One impor­tant event is the aster­oid impact that “reset” life on Earth 66 mil­lion years ago, which trig­gered a grad­ual cool­ing of the plan­et, and anoth­er was the tec­ton­ic move­ment that pushed togeth­er what we now know as Asia and the Indi­an sub­con­ti­nent. A result of these and oth­er unlike­ly occur­rences was the “bios­phere” in which we and all oth­er extant species live today.

What about you and me in par­tic­u­lar? Nei­ther of us, as Car­roll tells it here and in his book A Series of For­tu­nate Events: Chance and the Mak­ing of the Plan­et, Life, and You, should feel that our place was guar­an­teed. In human repro­duc­tion, when two par­ents get togeth­er and “that one lucky sperm makes it and com­bines with that one egg at that moment, that’s about a one-in-70-tril­lion event, genet­i­cal­ly speak­ing.” This can be dif­fi­cult to inter­nal­ize, since our own exis­tence is all we’ve ever known, in the man­ner of Adams’ sen­tient pud­dle. Even “as the sun ris­es in the sky and the air heats up and as, grad­u­al­ly, the pud­dle gets small­er and small­er,” it con­tin­ues “fran­ti­cal­ly hang­ing on to the notion that every­thing’s going to be alright, because this world was meant to have him in it, was built to have him in it.” There’s a les­son for human­i­ty in that sto­ry, and one that has­n’t become any less urgent in the past 27 years.

Relat­ed Con­tent:

Dis­cov­er “Jour­ney of the Uni­verse,” a Mul­ti­me­dia Project That Explores Humanity’s Place in the Epic His­to­ry of the Cos­mos

The His­to­ry of the Earth (All 4.5 Bil­lion Years) in 1 Hour: A Mil­lion Years Cov­ered Every Sec­ond

Big His­to­ry: David Chris­t­ian Cov­ers 13.7 Bil­lion Years of His­to­ry in 18 Min­utes

An Astronaut’s Guide to Life on Earth by Com­man­der Chris Had­field: The Viral Book Trail­er

Who’s Out There?: Orson Welles Nar­rates a Doc­u­men­tary Ask­ing Whether There’s Extrater­res­tri­al Life in the Uni­verse (1975)

Carl Sagan Presents a Mini-Course on Earth, Mars & What’s Beyond Our Solar Sys­tem: For Kids and Adults (1977)

Based in Seoul, Col­in Marshall writes and broad­casts on cities, lan­guage, and cul­ture. His projects include the Sub­stack newslet­ter Books on Cities and the book The State­less City: a Walk through 21st-Cen­tu­ry Los Ange­les. Fol­low him on the social net­work for­mer­ly known as Twit­ter at @colinmarshall.