Now that we have established what needs explaining (biological information, and the origin and functional interrelatedness of cellular machinery) and the scientific method biologists employ to formulate an explanation, we turn our attention to the four possible explanations for life’s origin: (1) Chance; (2) Necessity; (3) Combination of chance and necessity; (4) Intelligent agency.  In this post I will examine the possibility that life can be explained in terms of chance processes alone.

Just like the lottery, specific probabilities can be assessed for the origin of life by chance.  To illustrate how probabilities are assessed, consider a combination lock.  What are the chances of someone guessing the correct combination of a lock with four dials containing 10 digits each?  To determine the chances one must multiply the number of digits on each dial (10) by itself four times (because there are four dials): 10 x 10 x 10 x 10 = 10,000 different possible combinations.  The chances of guessing the correct combination, then, are 1 in 10,000.  If one more dial was added to the lock, it would decrease the odds by a factor of 10 (1 in 100,000).  If one is given only one try, the odds of getting the right combination are overwhelmingly against him—so much so that if the lock opened everyone would suspect that his selection was not random, but based on intelligence, or that the lock was faulty.  The odds of cracking the combination increase, however, as one increases the number of attempts.  If one is given 100,000 tries to guess the combination, then the odds are that he will eventually guess the combination through random attempts alone (if each try took 10 seconds, you could crack the 4-dial code in about 28 hours, and the 5-dial code in about 11 days).

Because the addition of every new part increases the odds exponentially, when you get into sufficiently complex objects like proteins and DNA, the odds of them forming by chance alone are effectively 0.  Why?  Because there is not enough time for even half of the possible “combinations” necessary to form a single protein to have been tested by chance alone.

The simplest living cell is Mycoplasma genitalium, a bacteria with 580,070 nucleotide base pairs, and 517 genes that code for 482 different proteins.  Scientists, however, think it may be possible for a cell to function with less DNA, and as little as 250-400 proteins.[1] This marks the minimal complexity for life.  So what are the chances that 250 functional proteins could arise by chance to form the first living cell?[2] To determine this we need to first establish the chances of forming even one protein by chance.

Some of the shortest functional proteins in the cell consist of at least 150 amino acids.  The chances of getting those amino acids to assemble themselves in the right sequence by chance alone is 1 in 1074.  To complicate matters, amino acids come in both left-handed and right-handed varieties (in equal amounts).  Life, however, only uses amino acids of the L-handed variety.  So in addition to the problem of sequencing the amino acids in the right order to form a meaningful biological “sentence,” protein formation on the pre-biotic Earth would have also faced the difficult problem of getting L-handed—and only L-handed—amino acids to bond with one another, for as soon as a R-handed amino acid bonded to a string of L-handed amino acids, protein formation would cease.  

The problem facing protein formation is similar to the problem of having to spell “I am going to Disney Land in California next Saturday with some friends and family who will be coming to stay with me for a couple of weeks from the venerable city of Venice, Italy” by randomly pulling letters out of a large pot one at a time.  Inside the pot, however, is an equal number of English letters and Chinese characters.  If I pull out an English letter that is not appropriate for the sequence, whatever portion of the sentence I was able to form purely by chance has to be discarded.  Likewise, if I pull out a Chinese character from the pot, whatever portion of the sentence I was able to form purely by chance has to be discarded.  The chances of being able to pull out the exact English letters in the exact sequence without ever pulling out a Chinese character is nearly impossible.  And yet that is what would be required for even the simplest life form to begin.  

What, then, is the likelihood that 150 L-handed amino acids would bond together without a single R-handed amino acid interfering, when there are an equal number of L-handed and R-handed varieties available?  It is equal to the odds of flipping a coin and it coming up heads 150 times in a row: 1 in 1045.  Add to this the odds of sequencing the 150 L-handed amino acids into a biologically meaningful/functional order (1 in 1074), as well as the odds of forming only peptide bonds between amino acids (1 in 1045), and we discover that the odds of forming a single, small protein are reduced to 1 in 10164 (a 1 followed by 164 zeros).[3] That’s 1 chance in 100 trillion trillion trillion trillion trillion trillion trillion trillion trillion trillion trillion trillion trillion trillion trillion trillion trillion trillion trillion trillion trillion trillion trillion trillion trillion trillion trillion.  To put this in perspective, there are only 1080 number of protons in the entire observable universe!  That means the chances of finding a specified particle in the observable universe are a trillion, trillion, trillion, trillion, trillion, trillion, trillion times greater than the chances of producing a functional protein consisting of only 150 amino acids.  And these are the odds of forming just one protein.  Since the simplest living cell requires at least 250 different proteins, the chances of forming the necessary proteins by chance alone is 1:1041,000!

But wait, you say, given enough time, couldn’t the odds be met?  No.  Given a liberal estimate, there have only been 10139 events in the entire universe since the Big Bang.[4] So even if every event in the history of the universe was devoted to building a single functional protein, the number of sequences produced thus far would be less than 1 out of a trillion trillion of the total number of events needed to give it even a 50% chance of success! And that’s just one protein!  The other 249 would still need to be accounted for.  Anyone who believes chance can succeed with these odds is being irrational.

Random chance cannot explain the origin of life, but what about necessity?  Can natural law explain it?  We’ll take up this possibility next time.

[1]Using knock-out experiments, the scientists who mapped the genome of M. genitalium concluded that 381 of the 482 genes/proteins are essential to its survival.  Of extant cells, then, the minimal complexity for life is 382 genes/proteins.

In even the simplest of cells approximately 20 proteins are needed to transcribe DNA, more than 100 proteins are needed to translate RNA into proteins, and more than 30 are needed for replicating DNA during mitosis.

[2]The chances of forming a protein by chance are roughly equivalent to the chances of forming the gene that codes for the protein by chance (the information content is equal as well), but most OOL researchers choose to calculate the odds of forming proteins because it is simpler.

[3]This figure does not take into account additional factors such as the odds of all 20 amino acids being produced in enough quantities and being in close enough proximity to form a protein.

One might wonder why the odds of forming a functional sequence of 150 amino acids is not 1:10195 since that is the sum of 20 multiplied by itself 150 times.  While that number does represent the odds of obtaining a specific amino acid sequence, we are only interested in the odds of obtaining a functional protein (and there are a number of sequences that will lead to a functional protein).  The odds of obtaining a sequence of 150 amino acids that can perform a biological function, while astronomical, are considerably better than the odds of obtaining a specific amino acid sequence.

[4]William Dembski calculated this figure by multiplying together the number of elementary particles (1080), the number of seconds since the Big Bang (1016), and the number of particle interactions per second (1043).