Evolution: the core of Biology
The key to understanding Biology is through the study of Evolution[1]. Evolution is what makes life possible[2]. How life started and how life came to be is all through the process of evolution. Evolution can explain how complex organisms came to be, how simple forms stay simple, and how organisms are related to each other. Evolution not only explains the development of visible morphological characters. At the molecular level, functions and forms of genes are influenced by the process of evolution as well[1].
To further understand how evolution is the heart of life processes, we need to understand the concepts and ideas that explain life: the theories of evolution.
History of Evolution
Before the conception of evolution, people believed in the paradigm of the 'Fixity' of species[4], that everything was created through Divine Conception[5]. The accepted idea is that every single organism was created as it is, nothing is mutated, everything is unchanging especially man[4].
In the 18th century, Carolus Linnaeus, a Swedish botanist, initially believed that organisms were created as how they appear in the present and that they did not evolve from an earlier form. When he studied hybrid forms of plants as the product of cross-pollination, he was not able to provide an explanation. This led him to entertain the idea that organisms could have evolved from earlier organisms[5].
During this time (18th century), other scientists have started to explore on the concept of changing organisms through time. George Louis Leclerc suggested that the Earth was 75,000 years old, and that man descended from apes. Erasmus Darwin, the grandfather of Charles Darwin, presented his theory that the Earth was millions of years old and that evolution exists[5].
The first evolutionist who publicly defended his ideas was the French scientist, Jean-Baptiste de Lamarck. He proposed the Theory of Use and Disuse[4]. He explained that organisms who constantly use a certain feature would lead to the development of such feature, while continued disuse of a feature will lead to atrophy. He proposed that the feature which has developed through continued use could be passed on the next generations changing that feature permanently over time. One example that Lamarck presented was the long necks of giraffes. He proposed that in the past giraffes have short necks. Giraffes were forced to stretch their necks to reach higher leaves. Continued stretching of the neck through many generations eventually produced the long-necked giraffes that we see today[4].
This theory was tested on rats. In a laboratory setting, rats' tails were cut off consistently through many generations. However, continued cutting of the tail did not produce offspring with no tails.
In the 19th centruy, the French scientist Georges Cuvier presented the concept of evolution though Catastrophism. He explained that evolution came about through catastrophic events, such as huge floods[6], that contributed to the extinction of earlier species. Such catastrophic events created a new environment and the development of species to replace the extinct ones[5].
The English geologist Charles Lyell, however, believed the opposite of catastrophism. He argued that changes in the Earth's surface has been influenced by slow changes since the beginning of time[5]. This theory is called Uniformitarianism or the Doctrine of Uniformity[5][6]. In this theory, the changes on the Earth's surface has been gradual and consistent.
The theory of uniformitarianism is influential in explaining the evolution of organisms. Uniformitarianism supports the idea of gradual modification of organisms leading to the development of diverse species.
The Theory of Evolution by Natural Selection was presented by an English naturalist, Charles Robert Darwin in 1859. Natural selection is the process by which organisms change over time as the consequence of heritable traits. These changes are necessary for the organism to best survive in its environment. In short, how organisms came to be is the product of "descent with modification". Living creatures of today are somehow related and connected to each other. Diversity came about because populations with modifications suitable for the changing environment were favored over others. This means that organisms with favorable modifications were fit enough to survive and was able to successfully pass on such modifications to the next generation. This is why the theory of natural selection is described as "survival of the fittest"[3].
Microevolution through natural selection
Microevolution is the gradual change over the course of many generations causing changes in morphological characters such as size and color[3].
Macroevolution through natural selection
Natural selection is also capable of producing a whole new species from the original ones by accumulating several modifications given enough time (i.e. millions of years). Examples of such are birds being descendants of dinosaurs, whales as descendants of amphibious mammals, and apes as ancestors of humans[3].
Sexual selection
This is when traits are passed on to the next generation on the basis of sexual preference.
Neo-Darwinism is the incorporation of the concepts of modern genetics to Darwin's theory of natural selection[3][4][7]. Genes being passed down from generation to generation through the process of natural selection produces offspring with fit genes. These genes undergo recombination and mutations caused by random errors during replication. Mutations and recombination of genes is where evolution happens. During the processes of mutation and recombination, natural selection selects beneficial genes and rejects the others, creating an individual with genes translating to characters that will best suit the individual to survive[3][7].
Types of Evolution
- Convergent evolution happens when the same adaptations evolve independently under similar pressures (i.e. the ability to fly by insects, birds, and bats)[8].
- Co-evolution happens when two species or groups of species evolve alongside each other where one adapts to changes in the other (i.e. flowering plants and pollinating insects).
- Adaptive radiation happens when species split into new forms when a change in the environment makes new resources available that create new environmental challenges (i.e. the different beak shapes of the finches in the Galapagos islands. Differences in beak shapes was due to the different kinds of food available for the finches.)[8].
References
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