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Natural Selection Process and Evidence of Evolution

Chapter 1

The first chapter of the book Why Evolution is True by Coyne is an introduction to evolution and how it is driven by natural selection. Charles Darwin coined the theory that all life forms resulted from evolution, which was largely propelled by natural selection, which bases on the hypothesis that evolution started in the past and still occurs now. The theory postulates that biological modification happens with two primary characteristics, i.e. variation and the struggle for existence (Coyne, 2010). Regarding the first case, random variations occur in individual organisms’ traits, which are then passed on to the offspring. Concerning the struggle for existence, prevailing competition or stress factors ensure advantageous traits that are preserved and disadvantageous traits that are eliminated. Darwin’s theory of evolution as driven by natural selection not only rates as the greatest idea of all time about the origin of species but is also true.

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A fundamental outcome of evolution by natural selection is that it compels researchers to assess various binaries like superior and inferior or advantages and disadvantages from a local perspective. The implication is that no traits are superior; there can only be traits that are suitable for a given cluster of situations. For instance, in an anoxic setting, the capability to utilize sulfates is more desirable than, for example, general intelligence. Within a species, organisms undergo specialization to exploit the environment in distinct ways, and over time the specialism culminates in divergence (Wang et al., 2018). Proving this, a group of birds living in environments with worms would adapt by evolving longer beaks. On the other hand, those in localities with nuts would evolve stronger beaks to crack and feed on nuts. Only the bird species that adjust through specialization would survive and transfer the advantageous traits to their offspring. However, those that are not able to adjust would die, hence the concept of the struggle for existence and natural selection.

Due to the struggle for existence, any advantage will be vital, however slight. In the long term, organisms with a slight innate advantage over the other will survive and pass the beneficial traits to their progeny. Through this process, Darwin claimed that a population will undergo modification by accumulating small but desirable advantages over long periods (Coyne, 2010). The offspring will then have better survival chances due to the preserved slight variation, a process Darwin referred to as natural selection. The descent with modification linked to natural selection would then form the basis of evolution as theorized by Darwin.

Chapter 2

The second chapter of the book by Coyne, which is titled “Written in the Rocks,” gives detailed evidence on evolution through natural selection based on fossil records. The fossil record offers reliable proof of systematic change over time, i.e. descent with modification through natural selection. One compelling piece of evidence is the geological arrangement of a sedimentary rock near Utah’s Paria River (Queller, 2017). A cross-section of the sedimentary rock layers depicts fossil deposits laid down through millions of years. The lower layers comprise older fossils, showing the organisms’ succession over time. Nevertheless, Darwin feared the uncommonness of intermediate forms between some primary groups of organisms.

Paleontological research has, however, identified hundreds of thousands of fossilized organisms occurring inside accurately dated rock layers, typifying succession of forms over time and manifesting several evolutionary transitions. For example, microbes of simplest forms (e.g. bacteria) already lived 3.5 billion years ago, but the oldest, more complex eukaryotic cells have been located in fossils covered in rocks roughly 2 billion years ago (Coyne, 2010). Complex, multicellular organisms, i.e. animals, plants, and fungi have been identified strictly in younger geological strata. For instance, fossilized shell-bearing animals as identified by paleontologists dated 540 million years ago. Simple fishes (vertebrates), amphibians, reptiles, mammals, nonhuman primates, earliest apes, human’s australopithecine ancestors, and modern human fossils dated back to 490, 350, 310, 200, 60, 25, 5, and 0.15 million years ago respectively (Coyne, 2010). The fossil data, therefore, offers dependable substantiation of descent with modification.

Darwin asserted that the fossil record looked so incomplete, full of bias, and too poorly understood to give strong evidence for or against natural selection. Nevertheless, the integration of paleontology in the study of rocks and the dating of fossils has yielded promising data. From the available evidence, it can be argued that no reversals will occur in future paleontological research. That is, amphibians will never come before fishes, nor reptiles after mammals, and complex life will not occur in geological records ahead of the oldest eukaryotes. Against this backdrop, the theory of natural selection as a driving force in evolution is justified.

Chapter 3

In chapter three of Coyne’s book, vestiges, embryos, and bad design are discussed as evidence for descent with modification, albeit with more emphasis on embryology, which entails the study of biological development starting at conception. Particularly, it is a major area of evidence for descent from common ancestry. Barnacles, for example, represent sedentary crustaceans with barely any similarity to the rest of the crustaceans such as copepods, shrimps, and lobsters. However, barnacles look exactly like crustacean larvae as they pass through the stage of free-swimming larvae (Queller, 2017). The semblance of larval stages reinforces the idea that all crustaceans share homologous parts and ancestry.

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In principle, embryos of more evolved organisms differ more from those of the primitive ones as they become more specialized. For instance, the embryos of humans have gill slits at early stages, thus representing the form of an adult fish that usually has a functional gill slit. Based on the principle, the presence of gill slits in the embryos of humans is an indication of common ancestry with fish (Coyne, 2010). Through comparative embryology, it has thus been demonstrated that all vertebrates develop similarly and diverge from a putative common predecessor.

Inferences regarding common descent obtained from paleontology and geology are also supported by comparative anatomy. For instance, there is a striking similarity between the skeletons of humans, bats, and mice irrespective of the incomparable lifestyles and environments of the aforementioned species. The resemblance of the animals in terms of bone is observable in every part of their bodies. The limb bones are parallel in structure and connection to each other, yet a mouse uses these to run, human applies the forelimbs in writing, while bats fly using the very limb bones (Wang et al., 2018). Structures that are similar in appearance but different in function are called homologous. The evidence noted in homologous structures thus points to a common ancestry before the process of descent with modification over long periods as driven by natural selection.

Scientists study homologous structures not only in bones but also in the rest of the body parts to uncover evolution through natural selection. The jaw and ear of mammals are examples utilized to appreciate common ancestry through transitional phases. The mammalian lower jaws have only a single bone, whereas the reptile’s ones have a number of them. The other bones present in the jaws of reptiles are homologous with those occurring in the mammalian ear (Coyne, 2010). Essentially, the conclusions on homologous structures provide valuable deductions about natural selection as a diver of evolution.

Chapter 4

Chapter four of Coyne’s book gives evidence on natural selection by offering detailed exposition on the geography of life as relates to evolution. The contribution of biogeography to the proof that evolution occurred through natural selection is a compelling one. Roughly 100,00 fungal species, 250,000 plant species, and 1,000,000 animal species have been classified, with each inhabiting a unique ecological niche or setting (Queller, 2017). Yet, questions arise why islands such as the Galapagos have life forms comparable to those on the proximate mainland but members of different species. Natural selection theory clarifies that biological diversity is a consequence of the offspring of local or migrant ancestors that are better adapted to the diverse environments in comparison to their predecessors.

The first case of geographical isolation on evolution was reported by Darwin after observing clear differences between Galapagos finches from island to island. Their populations occupying the various islands of Galapagos underwent separate evolution and thus split into about 15 distinct species utilizing dissimilar food sources (Wang et al., 2018). The island barriers prevented mating between populations of finches’ species, thereby stopping the exchange of genetic material and marking the start of separate evolution. The unique food sources from island to island also created selective pressures unique to every population of finches. Eventually, the various populations of finches in the Galapagos islands adapted by accumulating, preserving, and passing advantageous traits unique to each island to the offspring.

Another classical example that reinforces geographical isolation as evidence of evolution is the mammalian populations of South and North America. The area characterized the evolution of strikingly diverse native organisms in isolation until the isthmus of Panama emerged about 3 million years ago. Afterward, the porcupine, armadillo, and opossum (South American mammals) shifted to the north alongside several other animal and plant species. On the other hand, the mountain lion (North American mammal) migrated to the south along with other species (Coyne, 2010). Indeed, Darwin’s discovery of geographical distribution as a factor in the evolution of organisms has since grown stronger with progressing knowledge.

Chapter 5

In chapter five, Coyne discusses how genetics contributes to species adaptation through natural selection. The overriding principle is that selection is a process involving the accumulation of advantageous genes over a long period to facilitate better adaptations in a particular environment (Coyne, 2010). Hence, species do not evolve based on their will but rather, the environmental conditions at hand initiate a process of trait/gene alteration to enhance survival. Only species with the right form of genetic variation eventually adapt and survive.

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The genetic-based processes are involved in the creation of adaptation driven by Darwin’s theory of natural selection. First, the initial population must be variable, i.e. there must be considerable dissimilarities within a population, for instance, varied coat colors of mice. Second, a proportion of the differences must be of a genetic basis, i.e. the differences in phenotypic traits should be under the influence of genotypic traits which are heritable. Mutations occur on the genes to yield beneficial or harmful adaptations that select organisms for survival or extinction. Third, the genetic variation must impact an organism’s chance of leaving a progeny (Coyne, 2010). Whether the offspring survives depends on the genetic traits (adaptations) inherited from the ancestor.

Through natural selection, the array of genetic variants randomly generated by mutations is lawfully filtered. All the good traits are kept while the bad ones are winnowed, hence the argument that natural selection does not happen by chance. Therefore, it is a powerful force in the origin of species, as it promoted the accumulation of genes with a greater probability of being inherited by the offspring. Thus, it makes later organisms more complex and highly adapted to the environment than their ancestors (Wang et al., 2018). Essentially, natural selection is sufficient to justify all the variations observed in the fossil record.

Chapter 6

On how evolution is driven by sex, Coyne’s book gives comprehensive details in an easily discernible way. The driving principle is that natural selection works to ensure successful reproduction, with traits differing between males and females (e.g. songs, tails, and color in birds), i.e. sexual dimorphisms often emphasized. Nature’s law is that males compete for females, while females select males of their choice based on the former’s best traits. For example, male Irish elk use their huge antlers to fight for females while they select male widowbird mate partners with the longest tail. Males have to fight for or woo females as they have numerous sperms or pollen while females have to carefully select males with the best traits as they have fewer eggs (Coyne, 2010). Sexual selection is thus a differential investment in the cheap sperm or pollen and expensive eggs.

The good-genes theory is one of the best Darwinian explanations for sexual selection. The model posits that females must discriminate among the males and only mate with those having superior genes, thereby conferring better adaptations to the offspring. Darwin’s observation of male paradise and peacock birds wooing females by displaying their beautiful plumes was a classic example of sexual selection (Queller, 2017). Therefore, natural selection may frequently produce preexisting preferences which assist organisms in surviving and reproducing.

Chapter 7

Chapter seven of Coyne’s book is purely about the concept of how species originated, blending the ideas of Darwin’s descent with modification based on geographical barriers and speciation. Regarding natural selection, a single species undergoes notable modifications over time, thereby ending with different species with new genetic traits. Species are not only different in their physical appearance, but some barriers hinder them from interbreeding to produce viable offspring (Wang et al., 2018). It is thus the biological species that evolves as driven by the evolution of reproductive barriers under natural or sexual selection. As noted among the finches of Galapagos, species origin is an outcome of genetic barriers that emerge when geographically isolated populations take different evolutionary pathways.

If speciation greatly depends on geographical barriers, then lots of opportunities must have been presented through history to subject populations to isolation. An example of historical isolation is noted in the Galapagos islands by Darwin, which resulted in the emergence of fifteen different species of finches. Another example relates to the evolution of strikingly diverse native organisms in isolation (North and South America) until the isthmus of Panama emerged about 3 million years ago (Coyne, 2010). Through natural selection driven by genetic barriers related to sexual isolation, millions of species have arguably appeared on earth today, making the process more valid than ever.

Chapter 8

In chapter eight of Coyne’s book, the molecular basis of evolution is all but clear. Humans and apes are linked to a common ancestor based on comparable amino acid sequences in the DNA structure, as well as striking skull similarities and body physiology. The skulls of fossil ancestors are similar to those of man and increase in complexity from Homo erectus, Australopithecus afarensis, Australopithecus rudolfensis, and Homo habilis (Coyne, 2010). The comparisons of the aforementioned skull bones offer indisputable proof concerning human descent with modification from apelike predecessors, thus validating Darwin’s theory of natural selection.

In terms of a molecular basis, humans and chimps compare and differ in the gene sequence and gene presence, pointing to the genetic divergence from the chimpanzees. Variations in the amino acids synthesized by genes, the availability or lack of genes, the number of gene copies along the areas gene expression occur during development are all molecular indicators of common ancestry for humans and apes. Moreover, there are also distinctions in physiology (humans sweat more than any other ape and represent the only apes with concealed ovulation among females). Other differences include behavior (pair-bonding is reported among humans, not apes) and brain configuration and size, and language (human brains are more complex to allow the use of words in communication) (Queller, 2017). Regardless of human resemblance to apes, descent from an apelike ancestor entailed considerable genetic alteration, hence the relevance of natural selection in evolution.

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Chapter 9

Chapter nine of Coyne’s book is a summary of why evolution as theorized by Darwin is a true concept. The argument for the truthfulness of evolution is based on the verification of Darwinism. Pointers to the reliability of natural selection as a force in evolution are paleontology and geology, the geographical distribution of species, comparative anatomy, genetic variations, comparative embryology, physiology, and molecular biology (Coyne, 2010). The final argument is that while there are several controversies regarding the validity of evolution, none has eventually disapproved the theory of natural selection based on verifiable facts.


From the above considerations, it is remarkable to conclude that evolution by natural selection is true. Fossil records and paleontological studies have all indicated decreasing complexity of organisms from the latest (humans) to the oldest (bacteria). Embryological studies have also shown that some organisms (e.g. humans and fishes) have similar structures during early developmental stages after conception, implying they evolved from a common ancestor. Similar evidence is reported in comparative anatomy where homologous structures (e.g. forelimbs of humans and bats) are structurally analogous but serve different functions. It confirms that these species shared a common ancestor before taking varied evolutionary paths due to natural selection. Based on the aforementioned pieces of evidence, it is plausible to conclude that evolution by natural selection is true.


Coyne, J. A. (2010). Why evolution is true. Oxford University Press.

Queller, D. C. (2017). Fundamental theorems of evolution. The American Naturalist, 189(4), 345-353.

Wang, H.-Y., Chen, Y., Tong, D., Ling, S., Hu, Z., Tao, Y., Lu, X., & Wu, C.-I. (2018). Is the evolution in tumors Darwinian or non-Darwinian? National Science Review, 5(1), 15-17. Web.

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