specifically, where a modification to a single molecule can actually have a significant impact on the descendant generation. One specific instance would be a change to the molecular structure of the protein molecules that serve as markers for the replication process for a relatively long segment of the DNA molecule. In this case, it would seem that the induced change in the marker protein, or in its point of connection to the DNA molecule, could result in shifting the length of the DNA segment that is replicated, or perhaps impacting whether the segment is even replicated at all. In any case, the resulting change in the new generation might well be a major change in the new DNA molecule, rather than just a highly localized change. As with point mutations, such a major systemic mutation is likely to have a catastrophic impact on the construction of the new individual, probably rendering it non-viable. However, in very rare occurrences, this type of change might significantly affect the new individual, perhaps giving it some new characteristic that renders it better able to survive and reproduce within its environment. Since the mutation would be passed along to successive generations of this particular individual, the net impact over time might well be positive relative to continuation of the species.

In our first chapter, we briefly considered the work of Gregor Mendel in establishing the field of genetics. Through the processes described by genetics, the act of procreation provides a well defined approach for effecting changes among the resulting progeny. Individual characteristics of an organism derive from the set of genes that make up its genome. The gene for a specific characteristic can encompass some spectrum of allowed values for that characteristic. The spectrum of allowed values is termed genetic variability. It may be broad, meaning that a characteristic can present many different states or values. In other cases, the genetic variability that results from this process may be quite narrow and present only a very few states or values. Specific states of a characteristic are selected when DNA material from two parent individuals is contributed to the descendent generation individual. In the case of the human species, this is the result of the creation of the original zygote of an individual which requires a pair of each chromosome, with one chromosome of each pair derived from each parent. Chromosomes are differentiated DNA molecules in the cell: humans have 22 pairs of similar chromosomes, and one additional pair of chromosomes, similar in women (XX), and dissimilar in men (XY). The result is that replication of the zygote is then driven by a completely new DNA sequence relative to either parent. In some instances, an environment in which an organism exists can preferentially select for certain states or values. The resulting organisms so selected are said to benefit from genetic adaptation to that environment. To reiterate, this is a normal characteristic of sexual reproduction of a species.

Many of the traits found in individuals can vary in the extent to which they are represented in a new generation, depending on the characteristics of this new combination. This means that variances in different traits may have an impact on the relative reproductive success for the descendent generation. This essentially provides variations that can then be subsequently judged through natural selection. If natural body mass could have an impact on the survival of the individual, then natural selection might enhance the generational numbers of either larger mass individuals, or smaller mass individuals depending on the characteristics of the environment in which the individuals are found. It is probably obvious, but it should be noted that the greater the genetic variability found in a species, the greater is that species capacity to adapt to a changing environment through the process of genetic adaptation. Species with little genetic variability essentially don’t have the option of making as many changes to adapt, so there are fewer chances to make a good change when a change is necessitated by a new environment.

While we have obviously only skimmed the subject, we hope to have conveyed at this point some appreciation of the intricacies of the biological substrate of evolution in sufficient details to

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