The study explored the homological characteristics of 22 species. The organisms were human, pygmy chimpanzee, common chimpanzee, gorilla, orangutan, white-handed gibbon, macaque (Cercopithecine monkey), horse, bison, cat, dog, bird, bat, frog, rattlesnake, alligator, fish, whale, wolf, pig, bacteria, and cow. The species were categorized as mammals, reptiles, birds, fish, or amphibians. However, humans and apes were further classified as primates. Moreover, the research sought to determine whether the species share characteristics that link them to a common ancestor. The research hypothesis was that if the evolutionary path of the 22 organisms were traced, then a common ancestor would be observed.
Universal Genetic Code
The genetic code describes the sequence of DNA’s or RNA’s nucleotides that determine the particular amino acids’ sequence in the formation of proteins. Moreover, the system is almost universal among organisms and forms the basis for heredity. The mRNA uses three-nucleotide codons to specify the sequence of amino acids. Each of the codons complements the three-nucleotide anticodon of a tRNA. In addition, the tRNA has one amino acid connected to its other end. The attachment occurs through synthesis reaction with a synthetase enzyme acting as a catalyst. The genetic code is homologous for the 22 organisms; thus, it supports the research hypothesis.
Cytochrome C Data
The amino acid sequences are often used to determine phylogenetic relationships. Sequence studies that use functional genes focus on the ubiquitous genes of proteins to ensure independent comparisons of the species’ phenotype. When comparing the human protein sequence to a chimpanzee’s sequence, for example, it is expected that their proteins will be similar because the two organisms share various anatomical characteristics. However, one can also compare the sequences of fundamental genes, such as the cytochrome c gene. Such genes lack influence over particular chimpanzee or human attributes (Theobald).
Cytochrome c is a ubiquitous and essential protein occurring in both eukaryotic and prokaryotic organisms. The cellular mitochondria contain cytochrome c, which transports electrons in a primary metabolic process called oxidative phosphorylation (Theobald). The process utilizes oxygen to generate energy. Using the idea of a common descent, one can predict that chimpanzee and human cytochrome c sequences are similar. According to Theobald, chimpanzees and humans have a similar sequence of the cytochrome c protein. Hence, the high degree of similarity in the proteins corroborates the theory of common descent and the research hypothesis.
Genetic Distance between Primates
The difference in the DNA sequences among primates can be obtained by allowing DNA strands from two different species to join through complementary base pairing. Consequently, an increase in the similarity of their sequences increases the bonding between the two strands. Next, the DNA double helices are heated in order to separate them. However, relatively tighter bonds require a higher temperature to induce separation. The separation temperature of strands from two different organisms and the temperature of separation of two strands from similar species are compared. Similar organisms have a relatively lower temperature difference. Thus, the temperature difference can determine the phylogenetic relationship of the organisms. From the DNA-DNA hybridization, the distance between humans and chimpanzees is 1.64. Nevertheless, a range of 7.1 exists between macaque and humans, and between macaque and chimpanzees. Therefore, chimpanzees and humans have a relatively close ancestral relationship, which further supports the research hypothesis.
Transitional forms and appearances in geologic time scale
Fish are the initial vertebrates in the fossil record. The first land vertebrate, however, is a fossil amphibian called Ichthyostega. If amphibians came from fish ancestors, then we should see some intermediates among the fossils. Fortunately, the fossils of Eusthenopteron and Ichthyostega indicate the development of feet in the evolution of amphibians. Thus, a transition exists between a fish and an amphibian, which supports the research hypothesis.
The transition from the reptilian to mammalian species has an excellent record. In particular, fossils show the transition between different jaws. The middle ear of mammals has three bones while the lower jaw has only one bone. In contrast, the middle ear of reptiles has one bone while the lower jaw has several bones. Fossil species document transitional jaw-ear arrangements (White). For example, the Morganucodon has a reptilian remnant of a jaw joint. Transitional stages are also evident in features such as the ribs, vertebrae, skull, and toes. Fossil records, therefore, support the research theory of a common ancestor.
If reptiles and birds have a common ancestor, then a finding of intermediates is expected. Birds do not fossilize well because they have fragile and light bones. However, a well-known fossil of Archaeopteryx lithographica exists. The fossil’s characteristics show a clear transition from a reptilian to a bird species. Hence, the transition supports the research hypothesis.
Whale/Even-Toed Hooved Mammal Transition
Visually, the primary difference between land mammals and whales is that whales lack hind limbs. However, whales have a portion of the femur, as well as tiny pelvic bones that do not protrude from the body. Presumably, if whales evolved from mammals that lived in dry conditions, then the evidence of a gradual reduction of limbs should exist. Fortuitously, whale-like and whale fossils such as Ambulocetus natans and Basilosaurus isis show a transition from land mammals to whales. Basilosaurus isis, for example, had tiny but complete hind limbs. The whale fossils, therefore, support the theory that whales evolved from land mammals. Consequently, the existence of fossils supports the research hypothesis.
Svensson explains that apes appear during the Pliocene while humans emerge in the fossil record during the Pleistocene. Thousands of fossils showing an intermediate between humans and apes exist and have been classified in the family Hominidae. The hominids include the species of Australopithecus and Homo discovered in Africa. The existence of homologous features in the skulls of such ape-like and human-like fossils supports the theory that apes and humans emerged from one ancestor.
According to Svensson, the present organisms descended from cells that evolved nearly 3.8 billion years in the past (BYA). The sharing of the genetic code by almost all cells is one of the significant pieces of evidence that organisms have a common ancestry. Therefore, cellular processes are extremely similar in virtually all cells. Microscopic fossils show that the initial life forms were prokaryotic cells (Figure 1) that appeared between 3.5 and 3.8 BYA (Svensson). The cells were heterotrophic bacteria that utilized organic molecules occurring in the oceans.
2.5- 2.8 BYA marked the appearance of photosynthetic bacteria that combined carbon dioxide into simple sugars using light (Svenssson). Consequently, photosynthesis became the foundation of primary production in almost all ecosystems. The process yielded the oxygen that began accumulating in the atmosphere. Soon, oxygen became one of the essential components of metabolic pathways and established the ozone, which prevents the passage of harmful solar radiation through the upper atmosphere. The presence of oxygen and a radiation free environment allowed the appearance of the first eukaryotic cell, nearly 1.8 BYA (Figure 1).
Figure 1. Evolutionary tree of prokaryotes and eukaryotes. The figure describes the initial appearance of various organisms.
Fossils that are about 600 -700 million years old document the emergence of the first animals (Svensson). Later, a rapid increase in the numerical abundance of different animal species occurred in the Cambrian period (Figure 2). Therefore, the ancestral origins of present-day animals can be traced to the animal species of the Cambrian period. As the Cambrian period ended, the earliest vertebrates, which were jawless fishes, emerged. In the Silurian period, however, some of the groups of fishes evolved jaws. Consequently, the evolution of jaws established a significant adaptive radiation among the various fishes (Svensson).
As plants began colonizing the dry land in the Ordovician period, different species of land invertebrates began evolving. The invertebrates were primarily arthropods, which were followed later by the emergence of different insect species. However, the tetrapods or the first land vertebrates trace their ancestry to the fishes (Svensson). Some of the extant fish species show attributes that were important to amphibian ancestors. For example, the lungfish can utilize atmospheric oxygen while the Coelacanth has a fleshy fin whose bones have an arrangement similar to the limbs of land vertebrates (Svensson). Figure 4 and 6 show the phylogenetic tree of various vertebrates.
Later, reptiles evolved from amphibian ancestors and became relatively better adapted to land conditions. Their primary problems, however, were desiccation and reproductive challenges due to a lack of adequate water. Consequently, they developed a scaly and keratinized skin to prevent water loss. Moreover, they began producing amniotic eggs, evolved internal fertilization, and developed efficient kidneys in order to solve the challenge of inadequate water. Soon, mammals and birds emerged from the reptilian ancestors (Svensson). Figure 5 describes a phylogenetic tree of the various mammals that appeared during the Cenozoic. Finally, the Pliocene and the Pleistocene marked the emergence of apes and humans respectively (Figure 3 and 2).
Figure 2 shows a compilation of the Earth’s history based on dated fossil finds, as well as rock formations. In the Earth's history, durations are divided into eons, epochs, periods, and eras. Each of the divisions occupies a particular absolute time range computed in millions of years (MYA). Moreover, radiometric dating divides the Earth’s history into different durations and explains the time range in which individual fossils occur.
Figure 2. Geological Time Scale (Source: West Valley College). The figure describes the sequence of appearances of different organisms
Figure 3. Phylogenetic tree of primates (Source: Chen). The diagram describes the evolutionary relationship of primates
Figure 4. Phylogeny of vertebrates (Source: University of California Museum of Paleontology). The diagram explains an evolutionary relationship among various vertebrates.
Figure 5. Phylogeny of placental mammals (Source: Buell). The figure shows the evolutionary relationship of various mammals.
Figure 6. Phylogenetic tree of distinct vertebrates (Source: National Center for Science Education). The diagram describes the homologous features that unite various vertebrates.
The 22 different organisms that have been explored in the current study show various homologous features. The characteristics include the presence of a universal genetic code, cytochrome c protein, as well as transitional appearances and forms. Consequently, the similar features allow the establishment of a phylogenetic tree that traces the organisms’ history to a common ancestor. The presence of homologous attributes supports the research hypothesis that the 22 species evolved from one ancestor. Therefore, the study was successful because it supported the theory.
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