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Presentation on theme: "EVOLUTION."— Presentation transcript:


2 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.

3 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.

4 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

5 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


7 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

8 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.


10 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.

11 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 hand adapted for grasping whale’s flipper adapted for swimming wings of bats adapted for flying forearm of the horse adapted for walking They all have different functions but they are internally very similar

12 Homologous structures

13 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

14 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.

15 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.

16 Vestigial structures


18 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.

19 5. Embryological Evidence


21 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.

22 6. Comparative Biochemical and Physiological Evidence
For ex; cytochrome c, a protein molecule that every organism needs for cellular respiration differs between species.

23 Differences in amino acids from humans in vertebrate hemoglobin polypeptides

24 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.

25 6. Evidence from domestication

26 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.

27 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.


29 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.


31 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.

32 Lamarck’s Theory of Evolution
2. The Inheritance of Acquired Characteristics Lamarck 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.



35 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.

36 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

37 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.

38 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.

39 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.


41 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.

42 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.

43 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.

44 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


46 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.

47 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.

48 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. 


50 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.

51 Darwin’s Theory of Evolution
Natural Selection: Industrial melanism is the term used for the development of dark-colored organisms in a population exposed to industrial air pollution and it is an example of observed natural selection.

52 Darwin’s Theory of Evolution
Before England became industrialized, the light – colored moths blended in well with the lichens that covered the bark of the tree. As a result of this camouflage, birds that feed on the peppered moth could not easily find them. Dark – colored moths were easily eaten by the birds. When the air pollution killed the lichens and blackened the trees, light-colored moths became easy prey for birds.

53 Bacterial resistance to antibiotics
Darwin’s Theory of Evolution Bacterial resistance to antibiotics Antibiotics usually kill bacteria. However, once the use of antibiotics became common, resistant strains of bacteria began to appear. In a large population of bacteria, there are always a few individuals with resistance to the antibiotics. In an environment containing the antibiotic, only the resistant individulas will grow and reproduce. By natural selection, the strain with resistance to the antibiotic becomes the common type. A pure culture of bacteria can be tested for antibiotic resistance by evenly swabbing it over an agar plate and pressing discs of antibiotic into the agar. After a period of incubation, sensitivity or resistance to the antibiotic can be determined by measuring the zone that forms around the disc. Large zones mean the bacteria are sensitive to the drug, small or nonexistent zones are signs of resistance. (Image Courtesy: Centers for Disease Control and Prevention.)

54 Darwin’s Theory of Evolution
DDT resistance in Insects When DDT was first introduced, it was an effective killer of insects, including mosquitos. However, a small proportion of insects in various insect populations possesed a natural resistance to DDT. When the DDT – sensitive members of a population were killed by spraying, the DDT-resistant insects survived and passed on their natural DDT-resistance to their offspring. Evetually, many insect populations were completely resistant to DDT. DDT did not create the resistance of the insects. Rather, the DDT acted as the environmetal agent for the selection of the resistant strains.

55 Darwin’s Theory of Evolution
Speciation: Over many generations, favorable adaptations gardually accumulate in the species and unfavorable ones disappear. Eventually, the accumulated changes become so great that the net result is a new species. The formation of new species is called speciation.

56 Geographical and Reproductive Isolation
Isolation refers to anything that prevents two groups within a species from interbreeding. Isolating agroup of organisms seperates its gene pool from the gene pool of the rest of the species. Through mutation, genetic recombination and natural selection, a different gene pool will evolve in each group. New species Geographical isolation population Mutations,genetic recombinations, natural selection

57 Geographical and Reproductive Isolation
Geographic isolation occurs when a population is divided by a natural barrier, such as mountain, desert, river or other body of water, or a landslide caused by an earthquake. As a result, the gene pool of each group becomes isolated. Over a period of time, each group will become adapted to its particular environment.

58 Geographical and Reproductive Isolation
When the differences between the isolated groups become great enough, they will no longer be able to interbreed, even if they could get together. Fruit fly experiment suggests that isolating populations in different environments (e.g., with different food sources) can lead to the beginning of reproductive isolation. These results are consistent with the idea that geographic isolation is an important step of some speciation events.

59 Geographical and Reproductive Isolation
The Kaibab and Abert squirrel are formed by geographic and reproductive isolation. The Kaibab squirrel inhabits the north side of Grand canyon and the Abert squirrel south side. These two squrriel are thoght to be evolved from a common ancestor whose population was divided by Grand Canyon. After a long period of geographical isolation, these squirrels evolved. Although they are similar in appearance but they cannot interbreed.

60 Geographical and Reproductive Isolation
Differences may arise in courtship behavior, times of mating, or the structure of the sex organs.

61 Geographical and Reproductive Isolation
Events after mating like, inability of sperm to fertilize eggs, the death of the embryo, or the development of offspring that are sterile.


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