Replies

So how did the Cambrian explosion occur when thousands of critters just appeared?

Well if you consider a period of tens of millions of years as 'just appeared' then there are possible environmental, developmental, and ecological changes that might account for it.

I think your tens of millions of years is out of proportion.

Possible environmental, developmental and ecological changes might account for it is grasping for straws, unscientific and undocumented.

Well if you consider a period of tens of millions of years as 'just appeared' then there are possible environmental, developmental, and ecological changes that might account for it.

The premises of evolution: Organisms are “changed” by random mutations. Those “changed” organisms are either favored or disfavored by the environment and those that are favored survive better than those not so favored (survival of the fittest). Additionally, those more fit organisms are then more available for the next round of mutation and natural selection allowing generationally stepwise accumulation of mutations. Furthermore, according to evolution theory, these random mutations cumulatively produce more complex organisms and greater complexity is favored by the environment, i.e., is more “fit.”

Mutations are permanent changes in the DNA strand. DNA (deoxyribonucleic acid) is the information storage unit for all organisms. Mutations can only fall into three categories: beneficial, detrimental or benign (neutral). Beneficial mutations usually involve increased functionality in the organism. Such an increase in functionality must involve new information content in the DNA. Similarly, detrimental mutations usually involve loss of DNA information.

Observed mutation rates are low and, more importantly, the overwhelming number of mutations are detrimental (according to R.A. Fisher less than one in a million would not be detrimental). Therefore, the odds of a single, beneficial mutations are extremely low.

Stepwise increases in beneficial, organism complexity, i.e., a simple organism mutating into a more complex one, more fit for its environment and that organism, in turn, mutating into a yet more complex organism, and so on, require sequential beneficial mutations. If the chances were a million to one for the first beneficial mutation followed by the same odds in the next generation for the next beneficial mutation, there is now a probability with 12 zeroes after the decimal that the second step will occur. Of course, one must consider the population size, the occurrence rate of the “Goldilocks” mutagen (one strong enough to force a DNA change but not so strong as to kill the organism) and the generation time (how long it takes one generation to reproduce the next one), etc.

More complex organisms tend to have progressively longer generation times than less complex ones thus requiring increased time between mutations. This is just another way of noting that amoebae reproduce faster than dogs or cats. Additionally, more complex organisms generally produce fewer offspring per generation than less complex organisms. Again, just a way of noting that fish parent produce more fry per generation than elephants.

For a single-celled organism to evolve into something like a dog, new DNA information (not random base pairs, but complex and ordered DNA) would need to develop over time that would code for ears, lungs, brain, legs, eyes, etc. That is another way of saying the required number sequential steps of complexity becomes extremely long. If there is a probability, even, with only with 6 zeroes required at each step and even if the population is in the billions with a very low generation time, the likelihood that random mutations could achieve the result is not sufficient given billions of years much less only 10 million years.

Therefore, your implied assertion that enough time passed during the “Cambrian explosion” to account for the appearance of all of the phyla and species shown in the fossil record of this time frame does not appear adequate.