Natural Selection Versus Mutation

      Evolution is part theory and part proven fact.  The reality of natural selection, also called "survival of the fittest," is proven fact.  Survival of the fittest happens.  We can observe it.  When ecosystems change, the adaptable individuals live.  The non-adaptable individuals die.  Natural selection happens to bacteria when they become immune to penicillin.  Natural selection happens to fruit flies in the laboratory.  And for Charles Darwin, natural selection was the primary vehicle by which evolutionary change is accomplished.

      However, natural selection cannot be the only vehicle for evolutionary change.  That’s because natural selection only dwindles genetic variety.  It only destroys genetic information.  It cannot create any new genetic information.  As Kirschner and Gerhart point out,

 

There are some limits on what selection can accomplish.  We must remember that it merely acts as a sieve, preserving some variants and rejecting others; it does not create variation.[1] 

 

For example, if a gray moth lands on a soot covered wall in polluted 19^th century London, it will be more likely to survive if it becomes darker in color, such that it can be camouflaged against the dark soot.  Hence, over time, natural selection reduces its light colored genes, until that moth species becomes very dark.  However, if 150 years later, the British learn a lesson from the French, and switch from coal to nuclear power, then the buildings will become lighter in color, and the dark moths will have to become lighter in color again to blend in with their surroundings.  Yet, unfortunately for the moths, they lost all their light color genes during the previous round of natural selection, so they can only be dark now.  So the dark moths perch on the light colored walls, where they become easy food for birds.  The moths all get eaten and become extinct. 

      Therefore, if natural selection were the only vehicle by which evolution occurs, then extinction would reduce the number of species over time.  The amount of variation between living organisms would decrease, not increase.  Every time our environment changed, some unique species would get killed off.  Some unique gene would get obliterated.  Natural selection destroys life.  When it causes evolution, it only does so by annihilating genetic variety.  Survival of the fittest does not create new life forms.  It only destroys existing life forms.

      Yet earth history records that the exact opposite has happened to life.  The amount of genetic variety and the number of species has increased over time, not decreased.  If natural selection is the only cause of evolutionary change, then life would be decreasing in diversity.  Yet because we can observe from the fossil record that life is generally increasing in diversity, not decreasing, therefore some other powerful phenomena besides natural selection must be occurring. 

      Something is creating new diversity faster than natural selection can destroy it.  Something is injecting new variation into the gene pool faster than survival of the fittest can whittle it down.  Something is replenishing that which natural selection has destroyed.  Because the diversity of life has increased over time, not decreased, we know that there must be some force besides natural selection, which is even more powerful than natural selection, and this force creates new genetic variations faster than natural selection destroys genetic variations. 

      This force is mutation.  Genetic mutation is the creative force which is overpowering the destructive force of natural selection.  Even while natural selection whittles away at the gene pool, genetic mutation adds more to it.  Without mutation, natural selection would weed out genes until there was nothing more to weed out.  We are fortunate to be mutants, because otherwise, we would go extinct.  As Dawkins said,

 

Evolution by natural selection could not be faster than the mutation rate, for mutation is, ultimately, the only way in which new variation enters the species.[2]

 

But just how fast is the mutation rate?  Continuing with Dawkins:

 

DNA replicates so accurately that it takes five million replication generations to miscopy one percent of the characters.[3]

 

Scientific studies agree that the mutation rate is painfully slow.  One estimate gives the mutation rate as a range between one in 40,000 to one in 210,000 at any given locus.[4]  Another gives it by gene as 29-150 per million for fruit flies, 1.2-2.4 per million for corn, 8-30 per million for humans, and a staggering .07-5.61 per billion for E. coli bacteria.[5]  Another gives the mutation rate for eukaryotic DNA, which includes all plants and animals, as an order of magnitude in the tens of millions to billions.[6]  Another estimate puts the occurrence of base substitution rates per locus at a handful per billion.[7] 

      Not only is the mutation rate slow, but the vast majority of mutations are harmful, and do not directly result in an evolutionary advantage.  Thus, the chance that any given locus or gene will become a successful mutant is extremely slim.  Hence, evolution is believed to be possible only over millions of years.

      Given these probabilities, we should ask, is it possible that beneficial mutations could happen frequently enough to outpace the extinctions caused by natural selection?  Or are beneficial mutations so infrequent that we need some other catalyst for changing DNA, in order to account for the diversity of life forms we observe in nature?  Luckily for evolutionary theory, mutation has a knack for beating the odds.

 

DNA Base Mutations

      DNA is the blueprint for life.  Think of DNA as an encyclopedia.  Each volume of the encyclopedia is like a chromosome.  Chromosomes exist as single structures, like a book, yet no single chromosome is complete without the other "books" in the DNA "encyclopedia."  Each entry in the encyclopedia is like a gene.  Just as each entry in an encyclopedia contains information about a particular subject, so each gene contains information that codes for a particular function or protein.  Each word in the encyclopedia is like a DNA codon.  Each DNA codon is composed of only three DNA base pairs.  DNA base pairs are analogous to the individual letters of the alphabet, except there are only four of them instead of 26.  These four are A, T, G, and C.  These combine to form "words," which are always three "letters" long.  For example, a "sentence" in the DNA "encyclopedia" might look like this: 

TAG CAT GAG TAT ACT

      Genetic mutation occurs when one of the "letters" is changed.  Let's say the first codon in the example above, "TAG," undergoes a base pair substitution mutation, whereby the base pair "C" is substituted for the base pair "G."  Now, instead of "TAG" it reads "TAC." 

      Sometimes a substitution mutation like this causes the DNA "sentence" to change the amino acid it codes for.  If it does, it is either a "missense mutation" or a "nonsense mutation." 

      Missense mutations cause a change in the building materials of life.  They are analogous to changes in the blueprint of a building.  For analogy, you might get concrete in the kitchen sink instead of a garbage disposal, or duck tape to hold up the wall instead of nails.  Usually, these mutations are "deleterious," that is, "harmful." 

      Nonsense mutations are changes in the "punctuation" of the DNA "sentence."  They change the regulatory stop codons.  It is analogous to deleting a period at the end of a sentence, such that a run-on sentence is created, whereby it keeps going, on and on and on, until it reaches a the next period, eventually, which is a long ways away, kind of like this sentence.  The "period" at the end of a DNA "sentence" is actually a codon of three base pairs.  When a base pair substitution zaps one of these "periods," which are called "stop codons," then a nonsense mutation results.  Like missense mutations, nonsense mutations are virtually always harmful. 

      Besides base substitutions, there are also base deletions and additions.  These result in "frameshift mutations."  To illustrate a frameshift mutation, consider our example DNA string again: 

TAG CAT GAG TAT ACT

Now suppose that the "A" in "TAG" is deleted.  This causes all the base pairs to shift up, such that the DNA now reads: 

T'GC ATG AGT ATA CT

The meaning of every subsequent codon has been changed, and this will continue on down the line in the DNA string.  Frameshift mutations are extremely deleterious, because they compromise the integrity of an entire string of DNA.  However, DNA repair mechanisms often fix frameshift mutations by causing a compensating mutation to occur downstream from the original mutation.  This gets the DNA back on track.  For example, DNA repair might add another "T" after the third "T" in our example.  This repair causes the DNA string to read:

T'GC ATG AGT TAT ACT

Notice that the last two codons, TAT and ACT, have been changed back to the original.  Hence, these two codons, and every other codon downstream from them, are fixed.  However, the first three codons, TAG CAT GAG, have been changed to TGC ATG AGT, and this change will remain even after the compensating mutation.  Thus, frameshift mutations can result in permanent mutations even after DNA repair mechanisms have acted to compensate for them.

 

Hide and Go Seek

      Evolutionists believe base mutations like these are the root of what causes genetic diversity and the evolution of new species.  But these mutations happen very infrequently, and the vast majority of them are harmful, so can they really justify evolutionary theory?  For example, sickle cell anemia results from a base mutation.  Your chances of having it are extremely remote, but if you do have it, the effects are very detrimental.  But sickle cell anemia is an extreme example.  Many mutations are only slightly harmful. 

		Mutant Parent
		A	a
Non-mutant	A	AA	Aa
	A	AA	Aa

      What really transforms mutation into posivive evolution is the ability of mutation to play hide and go seek.  When cells divide, DNA copies itself so that each new cell has a copy.  But sometimes, DNA copies itself by accident.  The result is that you get two copies of the same string of DNA in a single cell, and the two copies continue together for millions of generations thereafter.  Many generations later, if a mutation occurs, that mutation will only affect one of the two copies.  Then there will be two different "alleles" for the same "gene."  Thereafter, if an individual with a mutant copy breeds with someone who does not have a mutant copy, their resultant offspring has a 50% chance of carrying the mutant copy.  In the adjacent chart, "A" represents the non-mutant copy, and "a" is the mutant copy.  The mutant parent has one original copy and one mutant copy of the DNA, so the offspring has a 50% chance of inheriting the mutant allele.  However, the non-mutant parent has only the original copy, and thus has a 100% chance of passing along the original allele to the offspring.

      Alleles account for a lot of the diversity we see in this world.  For example, alleles decide whether you will have blue or brown eyes, detached or attached earlobes, and whether or not you can roll your tongue.  Alleles are classified as "dominant" or "recessive."  Dominant alleles get primacy when deciding what physical features will manifest.  But if both copies are recessive, then the recessive allele will decide physical features. 

      What is particularly relevant to evolutionary science is that mutant alleles are normally recessive![8]  The implications of this are profound, for what it means is that even though mutations are usually harmful, they don't get a chance to express themselves very often.  In our example, the allele that carries the harmful mutation, "a," skips the mutant's offspring entirely, because the offspring's non-mutant parent gives the offspring a 100% chance of having a dominant and functioning allele "A."  Therefore, even though 50% of the offspring carry the mutant allele, none of them will be adversely affected by it.  In the next generation, assuming they don't procreate with their siblings, only 25% of the mutant's grandchildren will carry the mutant allele, and again, none of them will be harmed by it.  If the population size is large enough, and if incest does not occur, then the harmful mutation will be so diluted that it will hardly ever surface.  In this way, over vast aeons of time, a large number of mutations can accumulate in the gene pool of a species without harm, and without compromising the species' ability to survive. 

		Carrier
		A	a
Carrier	A	AA	Aa
	a	Aa	aa

      Occassionally, two carriers of the recessive "a" allele will procreate according to the adjacent chart.  There is a 25% chance that their offspring will be "aa," meaning that they carry only the mutant allele.  When this happens, the mutant allele will express itself, because there is no dominant allele present, and this will potentially cause severe harm to the offspring. 

      On the other hand, however, if the allele has accumulated favorable mutations since the original mutation, then it might just be beneficial.  Why might the mutant allele become beneficial?  The answer, it is hypothesized, comes from a DNA reshuffling process made possible by strings of DNA called "transposable elements."  Transposable elements are DNA segments that can move about, changing their sequential placement on a chromosome, and, as a result, sometimes radically alter stop and start codons, the recessiveness of alleles, and other meanings of the DNA.  Picture transposable elements as a deck of cards in a poker game.  If you don't shuffle the deck, you will draw the same hand every time.  If it's a loosing hand, you will always loose.  But if you shuffle the deck, you might just wind up drawing a full house or a flush every once in a while.  The movement of DNA as transposable elements on chromosomes is what shuffles the DNA deck.  It's what makes a loosing hand into a winner.  It's what transforms the harmful deleterious mutations into beneficial mutations.

      Given enough time, over millions of years, shuffling the DNA deck can produce zillions of winning hands.  In this way, we might explain the diversity of life forms evolution has produced – in spite of the scarcity and deleterious nature of the originally occurring mutations.

      Moreover, it may not even be necessary for two carriers of the recessive allele to breed.  A related hypothesis, which more plausibly explains evolutionary advancement by mutation, is that when the recessive mutant allele "a" accumulates subsequent mutations that enable it to produce a protein sequence that is not harmful, then that allele stops being recessive, and becomes a "wild-type" allele.  Wild-type alleles compete with the dominant allele "A" to actively make protein in the body.  When that happens, natural selection can begin acting upon the allele, selecting it, and tweaking the way it relates to the dominant allele, such that a new and different variety within the species is achieved.

 

Natura Non Facit Saltum

      Yet when a mutant allele becomes useful, it merely results in a new and different variety within the species.  It is not a radical mutant of a new and different species.  Only after many successful mutant alleles have accumulated in the gene pool can a species evolve into a truly new species.  Thus, evolution by means of mutation is necessarily a very slow and gradual process.

      Charlie Darwin had a saying:  Natura non facit saltum.  It is Latin for "Nature does not make sudden leaps."  It refers to the fact that evolution must necessarily happen gradually.  After 150 years, the science of genetics still supports Darwin's original opinion.  According to Levinton,

 

As a general rule, major developmental mutants give a picture of hopeless monsters rather than hopeful change… developmental mutants are of minor portent in evolution.  The side effects are too drastic.[9]

 

Most mutations are of relatively small effect and larger-scale mutations, though known to occur, usually reduce fitness.  Therefore, smaller-scale mutations probably are more important in evolution.[10]

 

Natura non facit saltum.  Even if mutant ninja turtles were to rise up from the sewers, the harmful effects of such large-scale mutations are too drastic to account for the emergence of new species.  Even if there were such mutants, which became new species from a single mutation, who would they mate with?  How would they continue the new species?  Unless two individuals, living in close proximity, underwent the exact same mutation with the same consequences, there is simply no way macro-mutations could explain evolutionary progress, because the macro-mutant would have no one to mate with.  Also, if such mutants do occur, where are they today?  We don't see mass mutants popping up and becoming highly successful new species in today's world.  Why would they have done so millions of years ago?  We don't observe new species spontaneously mutating from what came before in nature.  However, if we had been alive 530 million years ago, we would have seen them.