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Chapter 6 : The Process of Evolution

  2. HOMOLOGY AND EVOLUTION Homology is the existence of shared ancestry between a pair of structures, or genes, in different taxa. A common example of homologous structures is the forelimbs of vertebrates, where the wings of bats, the arms of primates, the front flippers of whales and the forelegs of dogs and horses are all derived from the same ancestral tetrapod structure. Evolutionary process is not a haphazard event in nature that simply happened in a short period of time. Evolution is almost close to the concept of change. To evolve means to change. This change, however, is not on the individual species but on the population. A lot of people find it hard to embrace the concept of evolution because they believe that it is opposed to their faith especially on the concept of creation.
  3.  The limbs are shaped differently because their lifestyles’ or how they live are different from one another. What is interesting, however, is that their forelimbs, have the same set of bones.  The limbs of animals called tetrapodor animals with four legs. However, not all tetrapods have four legs. Tetrapods also include animals without four feet such as whales and snakes.  They used to have limbs but have lost their them as they migrate or return to water and stayed there for some time.  Whales bones unearthed in excavation sites in Pakistan and Egypt showed that ancient whales used to have four limbs but eventually lost two of them specifically their hind legs. The front legs are now flippers.
  4.  Amphibians, reptiles, and mammals are classified as tetrapods. Humans are classified as tetrapods although we walk with only two legs. The ancestors of present-day tetrapods lived in the water. What is surprising is that they evolved from finned organism.  Homology simply indicates that although organism or animals are totally different, they have certain traits common to all of them inherited from a common ancestor.  They became totally different today from what they were before because they have evolved. Homologous structures are not only common in the animal kingdom;
  5.  The leaves of these plants are not the typical green leaves we see around us. Their function is not basically to perform photosynthesis but either to provide the plant with nutrients which the soil cannot provide or inadequately cannot give. Pitcher plant and the venus flytrap are carnivorous plants. They ‘eat’ insects. Poinsettia’s bright read leaves are called bracts to attract pollinators. The prickly spines of cacti are modified leaves to give them protection from animal predators and to shade them from heat. The shape and function of each plant in is different, yet, they are all leaves modified to help the plant adapt and survive their own unique environment. Modified leaves in plants are example of homologous structures.
  6. FOSSIL RECORDS AND EVOLUTION Some of the ratites. They are found in South America, Africa, Australia, Papua New Zealand. Like present-day birds are sometime called avian dinosaurs. Scientifically speaking, birds are reptiles.
  7.  It is interesting to know that the very first commercial ostrich farm in the country is located in Cagayan De Oro. It first opened in 1996 with just three pairs of breeding ostriches imported from Australia. The meat and egg of ostriches very high in protein but low in cholesterol compared to chicken.  Elephant birds are the largest bird that ever lived on Earth. They stand 10 feet tall and weigh more than 450 kilograms.  Elephant birds roamed Madagascar 60 million years ago during the time when birds ruled the Earth. They have strong and massive legs, long claws, and powerful neck. Their eggs which are about 170-200 times bigger than the chicken eggs, enough to feed a family for a day, were hunted for food (Extinct Animals, 2015).
  8. Marco Polo once wrote of a giant bird he saw in the late 13th century. Elephant birds existed until the 17th century. Their extinction was attributed to human activity. Collectively called ratites, elephant birds, like ostriches, rheas, kiwis, and all other birds, evolved from a two-legged carnivorous dinosaurs called therapods during Late Jurassic Period (University of California Museum of Palaeontology, n,d; Sanger, 2015). Two of the well-known members of the therapods are the towering Tyrannosaurus rex and the velociraptors.
  9. The existence of T. Rex, velociraptor, and other dinosaurs were proven by the discovery of their fossil remains. T. Rex fossils were discovered in places like Alberta, Canada and Texas (Castro 2016). The first velociraptor fossil was found in Gobi Desert, Outer Mongolia in 1923 by Peter Kaisen of the American Museum of Natural History (Castro, 2016).
  10.  The bones of the chicken is smaller and are proportioned to its size whereas the bones of Allosaurus are thicker and shorter to support its size.  Evolutionary biologists established that the transformation (evolution in terms of size and appearance) of the dinosaurs to modern day birds did not occur in a snap but gradual. Changes in features happen one at a time (Sanger, 2015).  Sanger (2015) described the transition as “first bipedal locomotion, then feathers, then a wishbone, then more complex feathers that look like quill-pen feathers, then wings.” Dinosaurs first transformed into a sparrow-size prehistoric bird called IBEROMESORNIS.  Fossil remains of Iberomesornis are found in Spain. According to www.prehistoric- (n.d), Iberomesornis ) “are considered to represent an intermediate stage in bird evolution before the appearance of,? More advanced forms closer to modern birds”
  11. EXTINCTION OF SPECIES  Everyday, a new species of plants or animals is being discovered. However, the sad part is many are disappearing faster before they can be studied in Science  You might have heard of Charles Darwin and how his historic five-years voyage aboard HMS Beagle including his visit to the island of Galapagos helped him formulated his theory of evolution.  His book Origin of Species contains his thoughts on evolution., and for this, Darwin is regarded today as the Father of Evolution.  Extinction is a serious threat to the perpectuation of life. It is not just an environmental problem confined in one location or in several locations in this planet.  It is a social problem that threatens our survival as human being because life on Earth is interconnected.  An invisible thread connects all creations on this beautiful planet. Everything is affected whenever one species vanished from the face of the Earth. When a species become extinct, it goes with it its own gene pool which is lost forever.
  12. DARWIN’S VOYAGE AND ON THE ORIGIN OF SPECIES AND THEORY OF EVOLUTION  Have you ever wondered how Darwin came up with his grand theory of evolution? Or what shaped his idea on evolutionary by natural selection?  Great ideas are always inspired by the things we see around us by own experiences. Sometimes, our ideas are influenced by what we read or hear. In his case, Darwin was heavily influenced by the things he saw on his five- year trip.  It should be emphasized that Darwin had already conceptualized the idea of evolution by natural selection long before joining the trip.  For Darwin, a naturalist, the distillation of his idea on evolution by natural selection is a product of so many things, foremost of which is his visit in the Galapagos Island aboard HMS Beagle, already on its second expedition.  Darwin was only 22 at that time when he was selected to join and a fresh graduate from Cambridge. His task, as a naturalist was to collect samples of plants and animals, including rocks.
  13. THEORY OF EVOLUTION BY NATURAL SELECTION Darwin’s ideas on evolution are extensively explained in his book “On the Origin of Species” published in 1859. His ideas created a lot od controversies especially with the religious authorities who found his views in conflict with the Bible on the idea of creation. The fundamental tenet of Darwin’s idea is that all the different species have evolved from simple organisms and that include humans. The first life, which is a single-celled organisms, evolved more than 3.5 billion years ago or about 1.5 billion years after the Earth was formed.
  14. NATURAL SELECTION IN ACTION  The theory of evolution states that evolution happens by natural selection. The concept of natural selection is very important in understanding evolution.  It is one of the basic mechanisms answer the question “How organism evolved?”  Nature, select the traits that have the best chance to survive and reproduce. These traits are encoded in their genes and are transmitted from one generation to another, that is, they are inheritable. Natural selection is nature’s gatekeeper or control quality mechanism.  The heritable trait is fur color. This is encoded in the genes, is transmitted from generation to generation. Heritable trait increases fitness. It enables the organism to survive and reproduce. Heritable trait like fur color that increases fitness called adaptive heritable trait. Adaptive heritable traits are important in natural selection. 
  15. AND ORIGIN OF SPECIES  The formation of different species of honeycreepers is an example of adaptive radiation, a rapid evolution wherein several new species is created from a founder species in a short period of time.
  16. SPECIATION  Study the figure. It is phylogeny that shows a polytomy. A polytomy is a node where several descendants emerge from a single ancestor. Whenever a phylogenetic tress shows a polytomy or polytomies, it conveys two things; available data are not sufficient to explain how it gave rise to several descendants or it is possible that a simultaneous speciation occurs among descendants. The case of honeycreepers is an example of a phylogeny showing polytomy.  Speciation describes how a new kind of plant or animal species is created. It occurs when a group within a species separates from other members of its species and develops its own new and distinct species is formed in the course of evolution.  To better grasp the concept of speciation let us first define the term species. A species is the basic category of biological classification. It refers to a group of organisms or individuals that actually or potentially interbreed in nature, This definition is totally different from the typical definition that defines species as;  “Composed of related individuals that resemble one another, are able to breed among themselves, but are not able to breed with members of an other species”.
  17.  There are five types of speciation in nature; allopatric, peripatric, and sympatric and artificial. 1. Allopatric speciation – occurs when members of a species are separated into two groups due to physical barriers. 2. Peripatric speciation – occurs when small groups of individual in a population separate from the larger group and form a new species 3. Parapatric speciation – occurs when a species occupies a large geographic area. 4. Sympatric speciation – occurs due to reproductive isolation. 5. Artificial speciation – occurs when human beings intervence in the natural reproduction using techniques or technology to create new species specifically for economic benefits.
  18. EXTINCTION OF SPECIES  Dinosaurs appeared 230 million years ago and ruled the earth for more than 135 million years. It was Richard Owen who first introduced the term dinosaur in 1842. The term is derived from two Greek words deinos, which means “terrible” “fearfully great,” and sauros, meaning “lizard” or reptile (Gammon, 2016)  Dinosaurs, the largest land animals that ever roamed the Earth, became extinct 65 million years ago. Everything we know about them was derived from the analysis of their fossils found in different parts of the world. Palaeontologists unearthed complete bones of heses reptiles in good condition giving us a good picture of how they looked like and lived. Dinosaurs are not the only extinct animals on Earth, there are many more including plants and other organisms.
  19. EXTINCTION Extinction is a serious ecological problem. The extinction of one species affects the rest of ecosystem because all creation are interconnected by an invisible thread of life. Extinction means end of the species. It occurs when the last member of the population dies.  A species is said to be extinct when no member of the species remains alive anywhere in the world. A species said to be extinct in the wild if the only surviving member is in captivity. A captive species is usually found in research of breeding centers.  On one hand, a species is said to be locally extinct or extirpated if it is no longer found in the area where it used to live and is found somewhere else. The species outside its natural habitat.  Darwin argued that extinction is a natural phenomenon as a consequence of evolution. According to him, extinction occurs whenever organisms fails to adapt to the changing and water.  This is true for normal process of extinction or natural extinction process. Causes if natural extinction process are demographic failure or genetic swamping, speciation or anagenesis. Anagenesis oranagenetic evolution is evolution within a lineage. It refers to the collective changes that transform one species into a different species with different characteristic. The increase in cranium size of humans is an example of anagenetic evolution.
  20. CAUSES OF NORMAL PROCESS OF EXTINCTION  The Earth has already experienced five main mass extinction events. Mass extinction is a rapid geologic even that takes place in a few million years. It occurs when at least half of all species die in a short period of time due to a catastrophic event like massive earthquake, comet and asteroid bombardments, glaciation, sudden global temperature change, or disease.  The largest mass extinction occurred 250 million years ago with 95% of all species were extinct. During mass extinction, old species are replaced with a new one.  Mass extinction is supported by fossil records. Palaeontologists at the American Museum of Natural History observed “fossils that are abundant in earlier rock layers are not present in later rock layers.”  A wide range of animals and plants suddenly died out, from tiny marine organisms to large dinosaurs. The sudden demise of dinosaurs of the Cretaceous-Tertiary extinction event (K-T event) that happened 65.5 million years ago, is an example of mass extinction.  Mass extension should not be taken negatively. It is a normal cycle of life in this planet. Mass extinction causes new life forms to emerge. For instance, the mass extinction of dinosaurs allowed mammals to diversity and evolve.
  21. EXTINCTION EVENTS  Palaecontologists recognize five main extinctions events, also known as the Big 5 1. The late Ordovician event 348 million years ago, when 100 families went extinct. 2. Late Devonian event 360 million years ago, when 30% of families went extinct. 3. End Permian event 245 million years ago, the biggest extinction of all the time when over 50% of all families were lost. 4. Late Triassic event 35% of families died out. 5. The Cretaceous Tertiary (K-T) event 65 Million years ago, which ended the reign of the dinosaurs.
  22. SIXTH MASS EXTINCTION  Scientists anticipate another mass extinction and call it the sixth mass extinction in the history of planet Earth. This expected mass extinction is being caused by destructive human activities (destructive fishing, land clearing, pollution, mining, etc) and uncontrolled population growth.  According to International Union for Conservation of Nature, destructive human activities have caused extinction of about 514 animal species since the beginning of the 15th century. It is during this period that Industrial Revolution started.  Extinction of plants and animals has irreversible consequences to humans. The potential of this organism as possible source of medicine for dreaded forms of cancer, hypertensions, kidney failure, depression, fever, etc., is forever lost.
  23.  Complete extinctions of plants in the rainforest is a serious environmental problem with huge social implications.  Marine organisms also face threat of extinction brought by destructive human activities. Our reliance on fossil fuels contributes to ocean acidification which has serious effects on marine organisms. For instance, coral bleaching is attributed to ocean acidification. As the ocean slightly becomes more acidic, the ability of shell-forming marine organisms like corals, oysters, shrimp, lobster, scallops, clams, and many planktonic organisms, and even some fish species is affected.  Ocean acidification also effect the size of shelled organisms, for instance, clams grow smaller. The rate of extinction of marine organisms is almost similar to the rate of terrestrial extinction. Signs that marine extinction is gaining ground are: decline in abundance of marine vertebrates of 22% decline in marine fishes by 38% and decline in population of baleen whales by 80 to 90%.