Which is that given the high mutation rates, how can it stay at that optimal peak when every single offspring will have inherited so many mutation (the majority deleterious, most only very slightly). Whichever one natural selection ''chooses'', it will still be less fit then it's parents were.
Let me try to answer this with a visualization in the mind.
First this optimal peak is an idealization which few, if any, individuals possess. It is the distillation of many thousands of optimals for all the various attributes that lead to evolutionary fitness (reproductive success). Think visual acuity, number of olfactory sensors, leg muscle strength, hemoglobin efficiency, and literally thousands of other attributes all combined in one ideal value.
Imagine a graph. Do not be concerned with the axes values, just see the graph. On this graph you draw this optimal vertical line. This is the line that represents the optimal value of all the attributes combined and is the maximum for reproductive success. Now impose the population bell curve for any specific attribute. Populations being what they are, the apex of the curve will be just off the optimum. Some of the population will have visual acuity less then others, some more and the average (apex) value of the curve will not be on the optimal line. The energy costs of better acuity may make it sub-optimal for this specific species in this environment so better acuity may not translate directly to increased fitness. Remember that fitness does not mean bigger, meaner, stronger. It means having more babies.
Now draw the thousands of other bell curves on the graph for all the other attributes necessary for reproductive fitness.
For each succeeding generation you must redraw each attribute's bell curve since population values at each point on the curve change. My son will have visual acuity up or down slope from me and my daughter may be on the opposite slope altogether. This is due to the different alleles present, mutations and any other mechanism of genetic change. This new curve for visual acuity will shift slightly from the past generation curve. All the curves will shift with each generation.
In aggregate, those individuals closer to the optimum for each attribute will have greater reproductive success which will keep the graphs of succeeding generations from straying too far off the optimal reproductive values.
What you end up with is, over many generations, these bell curves dance and wobble around this optimal line.
The optimal line will also shift in response to changes in the environment. If this optimal line around which all these attribute curves are dancing shifts slowly enough because the environment is relatively stable over
geologic timescales then this is a population in stasis.
Stasis is
not a period of no change either in the individual attributes' population curves or the central optimal line, but change slow enough to appear somewhat stable over geologic time frames.
The punctuated part of PE is when there is a radical shift in the environment which forces a radical shift in the central reproductive optimal line. And a radical shift in the environment also establishes new separate optimal lines on the chart (opens up new ecological niches).
Leave catastrophism out as a separate issue altogether.
The ancestor population will split with new sets of bell curves dancing and wobbling around each of the various optimal lines established for the changed environment and the opening of new niches. Speciation events have occurred.
What we see in the fossil record is an instantaneous arising of new species. The fossil record is dictated by geologic timescales when in fact the new species were established by the usual slow gradual evolutionary processes over thousands of generations over hundreds of thousands of years. Remember that 50,000 generations taking a million years to happen
is instantaneous in geologic terms and the fossil record.
Punctuated Equilibrium embraces evolutionary gradualism at it's core. What was new and radical about it was the recognition of long periods (geologic time) of populations in stasis versus the view of constant gradualism that came before it.
As long as the environment remains somewhat stable, the reproductive optimal line will not move too far too fast. It may slowly shift slightly one way or the other for a few hundred generations then slowly shift back for a few hundred more all in response to minor changes in the environment. On geologic timescales, in the fossil record, it appears to not move at all. No speciation events can be noted.
Mutation rates will affect the movement of the population curves around the reproductive optimal line and natural selection, in affecting reproductive success, will keep the curves from getting too far off the reproductive optimal center.
Edited by AZPaul3, : No reason given.
Edited by AZPaul3, : No reason given.