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EVOLUTION. E VOLUTION. Evolution means a gradual change over time. Since its formation about 4,5 billion years ago, the earth itself has changed continuously. This slow change is known as geological evolution.
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EVOLUTION Evolution means a gradual change over time. Since its formation about 4,5 billion years ago, the earth itself has changed continuously. This slow change is known as geological evolution. Many species also have changed since they first appeared. This process is known as organic evolution.
The theory of evolution assumes that the organisms living today are formed from some preexisting organisms that have changed over time. It also assumes that the change is a continuous process and the organisms that can adapt to the changing environmetal conditions will survive, where the ones that can not won’t. The basic idea of Theory of Evolution is that all species have a common ancestor.
EVIDENCE of EVOLUTION • Paleontological (fossil) Evidence • Evidence from classification • Morphological Evidence • Evidence from Vestigial structures • Embryological Evidence • Comparative Biochemical and Physiological Evidence • Evidence from domestication • Evidence from Cytology • Evidence from Geographical Distribution
1. Paleontological (fossil) Evidence • The study of fossils provides the strongest evidence of organic evolution. • A fossil is any trace or remains of an organism that has been preserved by natural processes. • Special circumstances are required for a fossil to form. • In the majority of fossils, the soft tissues of the organism decayed, and only the hard parts, such as bones or shells, have been preserved. • In some fossils, however, an entire organisms has been with almost no decay
Progressive series of fossils leading from an ancient, primitive organism to a modern form. Even though the fossil record is not complete (and is likely to never be complete) we can form a picture from the fossils we do have. Some animals are better respresented than others - like the horse
2. Evidence from classification • All organisms are arranged in taxonomic categories in modern biology and the similarities between different species are used to estimate the hereditary relationship between them. • Species sharing many of the same characteristics are believed to share a common ancestor.
3. Morphological Evidence • The presence of certain types of similarities offers evidence for the evolutionary relationships between species. • If living organisms are descended from a common ancestor, then closely related species should have more similar structures than distantly related species.
3. Morphological Evidence • Parts of different organisms that have similar structures and similar embryonic development, but have different forms and functions are called homologous structures. • Ex: human handadapted for grasping whale’s flipperadapted for swimming wings of batsadapted for flying forearm of the horseadapted for walking They all have different functions but they are internally very similar
The forearms of a cat, bat, whale and human are used for entirely different things (walking, flying, swimming, grasping) and yet they are composed of the exact same bones, just arranged differently and with slight alterations
4. Evidence from Vestigial structures • Vestigial structures are remnants of structures that were in an ancestral form of an organism. • In modern organisms, vestigial structures are reduced in size and serve little or no function. • In the human body there are more than 100 vestigial structures, including the coccyx (tailbone), the appendix, the wisdom teeth and the muscles that move the nose and ears.
4. Evidence from Vestigial structures • Ex: Both whales and phytons have vestigial hind leg bones embedded in the body wall. Apparently, whales and snakes evolved from four legged ancestors.
5. Embryological Evidence Embryos of closely related species show similar patterns of development. In vertebrate embryos, there are many similarities during the early stages of development. For ex; all of the embryos have gill slits, two chambered hearts and tails. These similarities support the idea that these organisms have a common ancestor.
6. Comparative Biochemical and Physiological Evidence • The more closely related the species are to one another, the greater the biochemical similarities. Because all DNA is descended from the DNA carried by the earliest life forms, the DNA of all organisms shares a common genetic code. These similar genes direct the synthesis of similar proteins in different organisms.
6. Comparative Biochemical and Physiological Evidence • For ex; cytochrome c, a protein molecule that every organism needs for cellular respiration differs between species.
Differences in amino acids from humans in vertebrate hemoglobin polypeptides
6. Evidence from domestication • For thousands of years humans have selected several species of animals and plants to domesticate. As a result, variations within the species occurred. • Today great variety of animals and plants are present which are produced by the hybridization methods. These organisms can mate with each other and produce fertile offspring and this indicates that these organisms are descended from a common ancestor.
7. Evidence from Cytology • Plants and animals are composed of cells that are similar in structure. This might prove that these organisms come from a common ancestor.
Endosymbiotic Theory • Chloroplasts and mitochondria are about the same size as bacteria (prokaryotes). • Both have a double membrane, a remnant of endosymbiotic event. • Both have circular DNA, genetic similarities to bacteria. • Both have their own ribosomes, protein synthesis machinery. • Similar biochemical organization.
8. Evidence from Geographical Distribution • The study of the past and present geographical distribution of organisms is called biogeography. It is concerned on how geological and climate changes can influence the distribution of species. • One of the basic idea of biogeography is that each species originated only once.
Lamarck’s Theory of Evolution According to Lamarck’s theory, evolution involved in two principles; • The Law of Use and Disuse: The more an animal uses a particular part of its body, the stronger and better developed that part becomes. At the same time, the less a part is used, the weaker and less developed it becomes. Ex: An athlete develops the strength of certain muscles by constant use.
Lamarck’s Theory of Evolution 2. The Inheritance of AcquiredCharacteristicsLamarck assumed that the characteristics of an organism developed through use and disuse could be passed on to its offspring. Ex: Ancestors of modern giraffes had short necks and fed on grasses. As the supply of food near the ground decreased, the giraffes had to stretch their necks to reach leaves of the trees. Their necks become longer from strecthing and this trait was passed on to their offsprings.
Weissman’s Experiment • Lamark’s second theory is incorrect as modern genetics has shown that the traits pass from one generation to the next but these genes are not affected by an individuals life experiences or activities. • The most well known experiment that tries to support Lamarck’s theory but failed, was performed by Weismann. • Weismann cut the tails off mice for 22 generations. In each generation, the mice were born with tails of normal length.
Modification All organisms have some changes due to the environmental conditions. These changes which are not hereditary are called modification. Lamarck’s second theory is actually about modification. Ex: Our skin gets darker in the sun
Darwin’s Theory of Evolution Darwin’s Observations Darwin made several types of observations during his trips to the South America coastlines and some islands.
Darwin’s Theory of Evolution The most significant of Darwin’s observations were those he made on the Galapagos Islands. He found many different species of finches living on these islands. The birds were alike, yet each species was slightly different from those on the next island or in another part of the same island.
Darwin’s Theory of Evolution Darwin made similar observations about many plants, insects and other organisms. While species on the Galapagos Islands resembled species on the mainland, they were always different in certain charactersitics. Darwin came to believe that these organisms originally had reached the islands from the mainland. Because of their isolation on the islands, the species had opportunities to develop special adaptations to each different region.
Darwin’s Theory of Evolution The six main points of Darwin’s theory are; 1.Overproduction: Most species produce far more offspring than are needed to maintain the population. Species populations remain more or less constant because only small fraction of offspring live long enough to reproduce. • Competition: Since living space and food are limited, offspring in each generation must compete among themselves and with other species. Only a small fraction can possibly survive long enough to reproduce.
Darwin’s Theory of Evolution 3.Variation: The characteristics of the individuals in any species are not exactly alike. They may differ in exact size or shape of a body, and so on. These differences are called variations. Some variations may not be important. Others may affect the individual’s ability to get food, to escape enemies or to find mate. These are vital importance.
Darwin’s Theory of Evolution 4. Adaptations: Because of variations, some individuals will be better adapted to survive and reproduce than others. In the competition for existence, the individuals that have favorable adaptations to their environment will have a greater chance of living long enough to reproduce. An adaptation is any kind of inherited trait that improves an organism’s chances of survival and reproduction in a given environment.
Adaptations Structural Adaptations involve the body of an organism. Ex: The wings of birds or insects are structural adaptations for flight. The fins of fish and the webbed feet of ducks are structural adaptations for swimming. Physiological adaptations involve the metabolism of organisms. Ex: Protein web made by spiders and the poison venom made by snakes
Adaptations Camouflage: The organism blends into the environment. Warning coloration: The colors of the animal make it unpleasant it to eat and protects it from predators. Mimicry: The organism is protected from its enemies by its resemblance to another species.
Adaptations In Mullerian mimicry, the model is not defined and several unpalatable species share warning colors or patterns to evade predation. Both models and mimics are toxic. Several species from several different orders may comprise a mimicry complex. The advantage is that the predators need only encounter one form to shun the entire complex.
Adaptations Batesian mimicry involves a palatable, unprotected species (the mimic) that closely resembles an unpalatable or protected species (the model). One example is this fly which looks like a bee. Birds know not to attack a bee as they will be stung.
Darwin’s Theory of Evolution • Natural Selection: In effect, the environment selects plants and animals with optimal traits to be the parents of next generations. Individuals with variations that make them better adapted to their environment survive and reproduce in greater numbers than those without such adaptations.
