Richard Charles "Dick" Lewontin (born March 29, 1929) is an American evolutionary biologist, mathematician, geneticist, and social commentator. A leader in developing the mathematical basis of population genetics and evolutionary theory, he pioneered the application of techniques from molecular biology, such as gel electrophoresis, to questions of genetic variation and evolution. In a pair of seminal 1966 papers co-authored with J.L. Hubby in the journal Genetics, Lewontin helped set the stage for the modern field of molecular evolution. In 1979 he and Stephen Jay Gould introduced the term "spandrel" into evolutionary theory.

Lewontin has worked in both theoretical and experimental population genetics. A hallmark of his work has been an interest in new technology. He was the first person to do a computer simulation of the behavior of a single gene locus (previous simulation work having been of models with multiple loci). In 1960 he and Ken-Ichi Kojima were the first population geneticists to give the equations for change of haplotype frequencies with interacting natural selection at two loci. This set off a wave of theoretical work on two-locus selection in the 1960s and 1970s. Their paper gave a theoretical derivation of the equilibria expected, and also investigated the dynamics of the model by computer iteration. Lewontin later introduced the D' measure of linkage disequilibrium. (He also introduced the term "linkage disequilibrium", about which many population geneticists have been unenthusiastic.)  In 1966, he and Jack Hubby published a paper that revolutionized population genetics. They used protein gel electrophoresis to survey dozens of loci in the fruit fly Drosophila pseudoobscura, and reported that a large fraction of the loci were polymorphic, and that at the average locus there was about a 15% chance that the individual was heterozygous. (Harry Harris reported similar results for humans at about the same time.) Previous work with gel electrophoresis had been reports of variation in single loci and did not give any sense of how common variation was.  Lewontin and Hubby's paper also discussed the possible explanation of the high levels of variability by either balancing selection or neutral mutation. Although they did not commit themselves to advocating neutrality, this was the first clear statement of the neutral theory for levels of variability within species. Lewontin and Hubby's paper had great impact--the discovery of high levels of molecular variability gave population geneticists ample material to work on, and gave them access to variation at single loci. The possible theoretical explanations of this rampant polymorphism became the focus of most population genetics work thereafter. Martin Kreitman was later to do a pioneering survey of population-level variability in DNA sequences while a Ph.D. student in Lewontin's lab.

Using a quote from the above article, answer the following question: What explanation did the paper talk about?
Their paper gave a theoretical derivation of the equilibria expected, and also investigated the dynamics of the model by computer iteration.