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The second concept that proponents of punctuated evolution stress is that of "narrow populations." They state that a new species forms only in communities containing very few numbers of a plant or animal species. According to this claim, large populations of animals exhibit no evolutionary development and can maintain their stasis. However, if some small groups leave these populations, they become isolated (generally assumed because of geographical causes) and can reproduce only amongst themselves. It is claimed that macro-mutations affect these small groups because they reproduce only among themselves, and so rapid "speciation" thus takes place.
Why do the proponents of punctuated evolution insist on the concept of narrow populations? The answer is obvious: Their objective is to "explain" the lack of intermediate forms in the fossil record. That is why their accounts insist that "Evolutionary changes took place in narrow populations and very rapidly, for which reason insufficient traces have been left in the fossil record."
In fact, however, recent scientific experiments and observations have revealed that in genetic terms, narrow populations are a disadvantage for evolution. Far from developing in such a way as to give rise to robust new species, narrow populations actually produce severe genetic defects. The reason is that in small populations, individuals continually interbreed, reproducing within a narrow genetic pool. For that reason, normally "heterozygotic" individuals become increasingly "homozygotic." Their normally recessive defective genes become dominant, and genetic defects and diseases increasingly emerge within the population. 45
In order to investigate this topic, chickens were observed for 35 years. These observations established that chickens kept in a narrow population became increasingly weaker in genetic terms. Egg production fell from 100% to 80%; reproduction rates from 93% to 74%. But through conscious human intervention—with chickens being brought in from other populations—this genetic contraction was reversed, and the basic chicken population began moving back in the direction of normality.46
This and similar findings clearly show that there is no scientific validity to the claim that narrow populations are the source of evolutionary development, behind which adherents of punctuated evolution find shelter. James W. Valentine and Douglas H. Erwin have stated the impossibility of new species forming by way of punctuated evolutionary mechanisms:
The required rapidity of the change implies either a few large steps or many and exceedingly rapid smaller ones. Large steps are tantamount to saltations and raise the problems of fitness barriers; small steps must be numerous and entail the problems discussed under microevolution. The periods of stasis raise the possibility that the lineage would enter the fossil record, and we reiterate that we can identify none of the postulated intermediate forms. Finally, the large numbers of species that must be generated so as to form a pool from which the successful lineage is selected are nowhere to be found. We conclude that the probability that species selection is a general solution to the origin of higher taxa is not great, and that neither of the contending theories of evolutionary change at the species level, phyletic gradualism or punctuated equilibrium, seem applicable to the origin of new body plans.47