text: creationists:  what mechanism limits evolution? we all agree that the following three statements are true:  1:  mutations occur in living organisms; 2:  of these, some are inherited; 3:  of these, some affect reproductive success.  if there is no limit to this process, then there is no limit to the change that evolution can achieve - by the incremental accumulation of millions of completely random insertions, alterations and deletions in the genetic code, each one tested against its environment by natural selection, a single-celled organism can evolve into a blue whale.  all that is required is resources - i.e. 4.5 billion years or so, and an entire planet to work with.  if creationists wish to dispute that evolution can do this, then they need to identify a mechanism which can limit evolution - something which allows a certain number or type of genetic mutations, but no more.  it needs to be a mechanism which allows the sort of evolution which even creationists do not deny, such as the evolution of new strains of influenza virus, but which stops the accumulation of changes beyond a certain point (and each creationist has their own idea of where that point is, e.g. at the species level, or genus, or whatever).  so, this is the challenge to the evolution deniers:  identify and describe the mechanism which limits evolution, showing how it controls mutations in the genetic code to prevent indefinite change.  if you can't do that then you have no business denying the evolutionary origins of living organisms. transmutation is a little used english word and biological term.  in plain english, it means to change the nature of something.  in biology, it means to change one species into another species; "speciation" is more commonly used.  transmutation is commonly used in nuclear physics where it refers to changing one element into another by changing the element's nucleus.  in the book, "macroevolution" steven stanley lists a half dozen confirmed speciation events which occurred in modern times.  one classic example of beneficial mutations is the peppered moth.  in its original form, about half of individuals were light and half dark.  when pollution darkened tree trunks, the light peppered moths stood out and were preferentially eaten.  the composition of the population shifted to mostly dark colored moths with only a few percent light colored ones.  additions to the genetic code of a species occur when an error during reproduction results in (1) part of the species' dna is copied twice and (2) dna from another species is incorporated.  icarus62's three statements do deal with microevolution.  what you don't understand, is that microevolution is simply macroevolution observed over a short time.  read his question!!  basically, he was saying, "we all agree that microevolution occurs.  given this, what is to stop macroevolution from occuring?"    to be taken seriously, creationists will have to do something other than nitpick at evolutionary theory.  they must develop theories of their own.  creationists are a laughingstock because they make no attempt at generating testable scientific theories, and then testing them.  icarus62, good job!