Geospiza And Advancement of Evolution Through Natural Selection

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Natural selection is an integral principle of evolution that has been improved upon through the observation of members of Geospiza, a species of finches native to the Galápagos Islands. By observing the interactions between various Geospiza species, Darwin developed his evolutionary theory of natural selection, a radical stipulation during his time. Establishing a single theory during his time is impressive, especially since evolution is not only a process, but also a mechanism of change. In addition to Darwin's research contributions, Peter and Rosemary Grant have also examined these fascinating organisms in order to draw concrete conclusions about evolutionary change. In stark contrast to the three week duration of Darwin's experiments, the Grants' research accumulated over thirty years, providing significant evidence for further support of Darwin's theories and for the development of new postulates on evolution. The cumulative data gathered from both Darwin and the Grants' research details the complexity and essence of natural selection, all from observations gathered on a single finch species ‒ Geospiza.


Natural selection is a facet of evolutionary knowledge that has been improved upon over the years, particularly through observing members of the Geospiza species of finches. Investigations involving these organisms first began with Charles Darwin, the father of modern evolutionary biology. Evolution had proved to be a confounding scientific concept preceding Darwin's time because of conflicting theories concerning the world's appearance. Were organisms always the way they presently were? Or did they evolve over time? From Darwin's experiments with Geospiza, the basis of modern evolutionary thought was formed and later expressed in his book, The Origin of Species by Means of Natural Selection (Campbell and Reece, 2009). In this masterpiece, Darwin discussed his primary theories on evolution, including that of natural selection (Riley, 2011). Although Darwin's beliefs were concretely sound, further research has also been beneficial. Peter and Rosemary Grant recently decided to delve even deeper into the realm of the Geospiza population, immersing themselves in their evolutionary developments over a period of thirty years. Their scientific findings have provided additional evidence to support Darwin's ingenious theory of natural selection, improving scientific knowledge in this field of study (Peter R. Grant et al, 2002).

Geospiza Contributions through Observations by Darwin and the Grants

In order to form an understanding of Geospiza's influence on natural selection, it is first necessary to explore the development of Darwin's evolutionary theory itself. By modern definition, evolution is the concept that all existing species are descended and differentiated from many ancestral species (Campbell and Reece, 2009). This phenomenon is not only a process, but also a mechanism of development over time. Thus, it is affected by a variety of factors, including environmental disturbances, genetics, geographical distinctions, and predator-prey relationships. During Darwin's era, however, the concept of evolution was drastically different and the principle of natural selection was non-existent. As a result, the evolutionary theories Darwin expressed were entirely original and, more importantly, radical, resulting in much controversy throughout the scientific community. The essence of Darwin's evolutionary theory first began to form as he voyaged around the world in the late 1800s. At this time, he came into contact with new lands and species, gathering specimens on his travels. Despite the vast array of scientific data he collected, the majority of his studies focused on the development of the Geospiza finch species in the Galápagos Islands, which lie off the coast of Ecuador in the Pacific Ocean. Over the course of three weeks, Darwin observed these birds, noting specific traits, such as beak size and food consumption, and environmental factors. What proved most interesting about these organisms was their diversity. Although all Geospiza shared a common lineage as descendants of the mainland species, there was considerable diversification due to the varying island environments. As a result, some finches were native to particular islands while numerous species inhabited others (Riley, 2011).

By observing the interactions between these species, Darwin developed his theory of evolution, which centered on the idea of natural selection. Natural selection is the principle that organisms with desirable adaptations will be selected to survive and produce offspring with those advantageous characteristics (Campbell and Reece 456). Through his observations, Darwin noted that Geospiza species that inhabited the same island often encountered the obstacle of competing for food sources. After measuring various factors, Darwin came to the conclusion that an organism's survival was due to their specific adaptations and the environment in which they were living. For example, if one island primarily had small seeds, birds with small beaks would be more likely to thrive, or be selected for, and vice versa. Darwin hypothesized that the birds with the most effective adaptations would reproduce at a higher rate, thereby passing on their traits to their offspring and improving the proficiency of the species. These conclusions became an integral part of Darwin's theory of evolution, particularly in his principles of natural selection and survival of the fittest, in which the most adept organisms survive and endow future generations with their adaptations through reproduction. He believed that this process continued over a long period of time, therefore making it impossible for humans to observe such change (Riley, 2011). Although his theory was relatively based on prediction rather than actual fact, the idea of natural selection was revolutionary. Thus, preliminary Geospiza observations enlightened the world to the concept of evolution and provided a basis for the future development of the natural selection principle.

Although Darwin's research was accepted as accurate, further experimentation was conducted by Peter and Rosemary Grant over a hundred years after Geospiza was first observed, providing concrete evidence for the theory of natural selection. Like Darwin, they studied the Geospiza species of finches. In contrast, however, they decided to focus on the specific species of Geospiza fortis, a medium ground finch on the island of Daphne Major (Riley, 2011). Beginning in 1973 and continuing until 2001, they captured these species and took various measurements, including beak size, body size, and beak depth, in order to identify the G. fortis group (Peter R. Grant et al, 2002). The Grants hypothesized that over time, there would be absolutely no change in these characteristics and that the species would remain undiversified. This, however, was soon proven false (Riley, 2011).

Over the course of their experiments in the Galápagos, the Grants observed many changes in the Geospiza species, many of which reinforced Darwin's evolutionary theory of natural selection. Their first observations centered on a period of drought during 1977, which resulted in a shortage of smaller seeds. In this experiment, the Geospiza with larger beaks were selected for because they could easily open the seeds and obtain food. Clearly the size of the Geospiza's beak reflected the types of seeds it ate. Thus, a correlation between adaptations and environmental influence was developed. In addition, the Grants observed that many Geospiza perished because of insufficient adaptations. As a result, the selected Geospiza reproduced and bore offspring with the most advantageous characteristics, validating the theories of natural selection and descent with modification (Riley, 2011). Additionally, the Grants discovered that adaptations could be reversed if environmental conditions provided for it. In 1984, the complete reverse of this selection occurred. Instead of selecting for larger beaks, smaller beaks were more desirable, resulting in the survival of Geospiza with this adaptation. Thus, it was established that traits could not only be selected for and changed, but could also be reversed to reflect a prior adaptation (Riley, 2011).

In two other experiments, however, the Grants were able to develop new evolutionary theories, hybridization and character displacement, which provided further evidence for natural selection. The first of these studies focused on Geospiza hybrids, birds exhibiting a combination of two adaptations due to an "interbreeding of species" (Peter B. Grant et al, 1992). In this example, instead of specifically having either a large or small beak, the bird might have a medium-sized beak. Through this study, it was discovered that one in ten species of Geospiza are hybrids, an indication that this process was relatively common in nature. In addition, hybrid Geospiza typically had better fitness than ordinary birds of its species, providing evidence of natural selection over a short period of time (Peter B. Grant et al, 1992).

In the second of these studies, the Grants established the term of character displacement, or a divergence in which one trait is selected for over another (Peter B. Grant et al, 2006). This study focused on a group of Geospiza fortis from the island of Daphne Major. In 1982, this species was exposed to Geospiza magnirostris, a group of ground finches with large beaks. Although there was no immediate impact on G. fortis, a drought occurred in 2004, which drastically reduced the food supply, thereby altering the finches' environment. As a result, the only seed species left was Tribulus cistoides, which were relatively large in size. This study further reinforced the theory of natural selection because many of the G. fortis species died due to selection for birds with large, strong beaks ‒ G. magnirostris. In addition, it was clear that there was competition among species since G. fortis perished due to its inefficient adaptations (Peter B. Grant, 2006). The idea of character displacement is also reinforced by the cumulative data collected over the period of thirty years in which the Grants experimented on the finches. During this time, the Grants observed an initial decrease in body and beak size, then an increase, followed by another decrease. In addition, beak shape became rather pointed during the 1980s, remaining so for about fifteen years following. These observations illustrate the occurrence of character displacement in the Geospiza species as well as the different rates of natural selection for various traits.


Natural selection is a primary principle of Charles Darwin's theory of evolution, which was originally based on conjecture. Despite this, the majority of knowledge concerning natural selection has been deduced from the studying of the species Geospiza, a medium ground finch from the Galápagos Islands. Both Darwin and Peter and Rosemary Grant spent a considerable amount of time examining these organisms in order to draw concrete conclusions about evolutionary change. Although Darwin's experiments spanned a period of three weeks, the Grants' research accumulated over thirty years, providing significant, concrete evidence to further support Darwin's theories. Through their research, the essence of natural selection has been established. The scientific world now knows that natural selection can occur at different rates, either quickly or gradually, due to various factors, including environmental conditions, hybridization, and competition among species. The element of adaptations has also been expanded upon, detailing how character displacement can occur and recur in a species over generations. In addition, it is clear that adaptations are not constant and instead change due to environmental conditions, i.e. the selection for G. fortis species with large beaks during a drought (Peter B. Grant et al, 2006). Finally, the cumulative data gathered from both Darwin and the Grants' research details the complexity of natural selection and the continued research being done on Geospiza in order to benefit the scientific community.