Grant, Peter, Rosemary Grant, and Kenneth Petren. “The Allopatric Phase of Speciation: The Sharp-Beaked Ground Finch ( Geospiza difficilis ) on the Galapagos Islands.” Biological Journal of the Linnaean Society 69.3(2000): 287-317. Print. Speciation can be defined as a prolonged course of differentiation that ultimately causes the absolute termination of the genetic switch between two populations originating from a common antecedent. Speciation takes place in two transitional stages that entail the creation of a pair of allopatric or parapatric populations. Grant, Grant and Petren (288) sought to understand the mechanism and cause of differentiation. They also cited that little information was available to enable the forecasting of those two fates during speciation. The authors studied disparities in physical attributes and the vocalization of Geospiza difficilis and used the dissimilarities to figure out the course of differentiation in allopatry as the initial phase of speciation. The authors used microsatellite DNA variation, morphological measurement and sonograms made from tape-recordings in the field to examine phylogenetic relationships of G. difficilis . Microsatellite data were amalgamated at 16 loci and used to develop a phylogenetic relationship at the species level. The authors carried out univariate and multivariate testing on structural data to exemplify and relate the alignment of structural segregation amongst groups of G. difficilis. The authors realized that the morphology of the finches’ beaks changed with respect to time and availability of different foods. Natural and sexual selection led to changes in vocal traits, which were independent of the size of the beaks. The authors concluded that physical attributes, vocalization and genetic qualities did not change consistently among the six populations of finches. They recommended that G. difficilis should be renamed as a new species G. acutirostris based on the principles of phylogenetic species. Podos Jeffrey and Nowicki Stephen. “Beaks, Adaptation, and Vocal Evolution in Darwin’s Finches.” Bioscience 54.6. (2004): 500-510. Print. Experimental studies show that beaks change by natural selection due to alterations in native environmental conditions. Additionally, recent studies reveal that beaks serve a practical function in the production of songs in songbirds. Podos and Stephen (501) aimed at demonstrating how studies on the connection between beaks and song provide fresh insights into the interaction of morphological acclimatization and the advancement of communication signs. The authors performed a detailed literature analysis of written material, literature and experiments on beak, sound production and the squeak of the finch. In their analysis, the authors examined and compared various vocal mechanisms in birds and vertebrates (505). They explored Darwin’s finch songs especially their structural features such as annotation and syllabus. Ultimately, they correlated literature on diversity and functions of beaks with song production. The authors used the available data to formulate the premise that the differences in the beaks of Darwin’s finches had an impact on their eating