Why a formidable challenge? Again, because random mutations alone must produce exceedingly rare functional sequences among a vast combinatorial sea before natural selection can play any significant role. As I discussed in Chapter 10, every replication event in the entire multibillion-year history of life on earth could not generate or “search” but a minuscule fraction (one ten trillion trillion trillionth, to be exact) of the total number of possible nucleotide base or amino-acid sequences corresponding to a single functional gene or protein fold.
