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Evolution P.1 Evolution – Diversity vs Unity O ne of the most striking facts emerging from a study of natural history is the v_____ of life; another, paradoxically, is its underlying u____. Of the two million or more species of organisms alive today, each can be grouped with others which it resembles. The natural class______ of organisms according to their sim______ suggests that organisms are related. The Creek naturalist and philosopher, Aristotle (384-322 B.C.) put forward the view that there was a grad___ change in living forms from plants to animals to man. This was the first recorded hypothesis that biological ev______ had occurred, that is that living organisms are descended from earl___, different ones#. # An alternative viewpoint is that each kind of organism alive today was created separately and has not altered since its creation; that there is no relationship by descent between living forms. This hypothesis is called 'Special Creation'. e.g. the Bible declared that each living thing was ‘brought forth after his kind’ and the usual interpretation of the statement was a literal one: that a ‘kind’ or species was unchangeable. Theories of the Origin of Life (reference) The major theories accounting for the origin of life on Earth are: 1. life was created by a supernatural being at a particular time (Special creation); 2. life arose from non-living matter on numerous occasions (Spontaneous generation); 3. life arrived on this planet from elsewhere (Cosmozoan); 4. life arose according to chemical and physical laws (Chemical / Biochemical evolution). II) The Idea / Theory of Evolution The term 'evolution' has a special place in the study of life. It has become the unifying concept of biology. Evolution implies an overall grad___ development which is both ord____ and seq______. In terms of living organisms it may be defined as 'the development of com______ organisms from pre-ex_________ sim______ organisms over the course of t_______'. # The idea of evolution did not begin with Darwin. The concept of continuity or gradual development of more complex species from pre-existing simpler forms had occurred to several philosophers and naturalists before the formal declaration of evolutionary hypotheses in the 19th century. Evolution P.2 II) Evidence for Evolution It is impossible to directly observe evolution that had taken place over millions of years, indirect or circumstantial evidence is what we have to evaluate. A) Evidence from Geographical Distribution of Plants and Animals Plants and animals are not evenly dist_______ around the world, identical conditions in different parts of the world often have diff_____ characteristic animals and plants. This ‘discontinuous’ distribution is interpreted as the result of years of evol________ events and suggested the idea of the common des_____ of species. a) Long-separated Continents Organisms, living in the same or very sim____ environmental conditions, often acquired sim____ adap____ structures and lifestyles. The tendency of un_______ organisms to acquire sim___ adaptive features is known as con_______ evolution. Examples of convergence are found in continents which have been iso_____ for a long time. Frequently different lines of evolution appear to converge from divergent starting points, so that similar niches are occupied by unrelated organisms. The best example comes from comparisons of the natural history of Aus______ with that of other continents. Australia has many species of pou____ mammals (marsupials), but virtually no true (placental) mammals. Yet Australia has a climate and habitats highly favourable to pla______ mammals, for when these are introduced there they have been very successful. eg. sheep & rabbit. Thus Australia has mar_____ ‘moles’, ‘mice’, ‘anteater’, and ‘flying squirrel’ occupying ni____ similar to those of their placental counterparts in other continents. They are NOT cl_____ related but come to look alike as a result of c_________ evolution. The explanation lies in the geographical iso______ of Australia, the result of continental drift. Australia became isolated at about the time the mar_______ and pla______ mammals diverged from a common anc______ (about 120 million years ago). In the absence of comp_____ from placental mammals, the marsupials have evolved into dif_____ forms that fill in all available n_____ in Australia. Evolution P.3 Q. What do you think are the marsupial counterparts for the following placental mammals ? Placental mammals Mole Anteater Antelope Flying squirrel Rabbit b) Australian Marsupials Placental mammals Prairie dog Hyena Marsupial mouse Sloth cat Australian Marsupials Volcanic / Oceanic Islands When Darwin travelled on board the Beagle he studied the flora and fauna of islands, and observed that islands often have unique species but are nevertheless seems closely related to those of the nearby mainl____. The rational explanation for this 'discontinuous' distribution was that species originate (evolve) in given areas and may subsequently disp_____ outwards from that point. The range of form in finches that Darwin observed in the Galapagos Islands during the voyage of the Beagle was explained in terms of adaptive r________. There are 14 species, the variations in b____ morphology reflect differences in feeding habits. Darwin suggested that these Galapagos finches were all closely rel____, in spite of their differences. It was suggested that soon after the islands were formed they were populated by a flock of finches from the mainland. These then evolved to fill the av________ ni_____ It is nearly always possible to see evolutionary links between an is____ inhabitants and those of the nearest cont_____ but, since sea provides an effective bar for most of the time, the island organisms evolve inde__________. Barriers, including the sea, mountain ranges, deserts or simply an unfavourable temperature range are essential to the div___________ of life. Thus from the geographical distribution of plants and animals, it can be concluded that: B) Species ori________ in a particular area; Species dis_______ outwards from that area; Dispersal could only occur for those species where land masses were close enough together to permit dis_____; Physical b_______ such as the sea lead to separation of new varieties and their an______; This genetic isolation leads to separate gene p____ and evolution of new sp_____. Evidence from Fossil Record Palaeontology is the study of plants and animals of the geol_____ past, as represented by their fossil remains. Fossils are the dead re_____ of plants and animals, pres_____ in sedimentary rock, in waterlogged peat or in the sticky gum that exudes from certain trees. Palaeontologists are able to place layers of sedimentary rocks in order of their formation and they can estimate the a__ of each layer from the thickness of the rock above and from carbon-dating techniques. In this way, a geological t____ s____ can be made. Oldest fossil-bearing rocks contains very f___ types of fossilized organisms and they all have very si____ structures. Younger rocks contain a greater v______ of fossils with increasingly comp structures. Evolution P.4 Throughout the fossil record many species which app____ at an earlier period disapp_______ in the younger rocks. This is interpreted in evolutionary terms as indicating the times at which species org______ and became ex______. The most convincing fossil evidence is found in cases where, in succ______ layers from one locality, a series of fossils exhibits grad_____ change. Good examples of this are seen in the evolution of the oyster and in a species of sea-urchin, where complete records of most intermediate forms are seen as fossils in successive strata. Intermediate forms of animal and plant organisation may be interpreted as the l____ between related groups of species. A possible example of an intermediate form, discovered in the fossil record, is Archaeopteryx, a 'missing link' between reptiles and birds. Fossil record tells us the seq______ and tim____ of the appearance of the major phyla, it support a theory of prog____ increase in complexity of organisms and against the idea that species cannot be ch . Q. One of the major criticism of using fossil as evidence is the lack of a continuous fossil record. Gaps in the fossil record - Missing link’. How would you explain the incompleteness of the fossil record ? C) Evidence From Comparative Anatomy Comparative anatomy is the study of the str________ similarities and differences between different species in order to set up the evo_________ relationship between them. a) Homologous structures and Divergent evolution (adaptive radiation) Organs of some animals are fundamentally the same in str_______ and anat_____ positions, but they have adapted to dif______ functions. Such organs are said to be homologous. The presence of homologous organs suggests a com ancestry. Evolution have occurred in which modifications of the fundamental structural plan to perform different functions in different environment. The evolution of div_____ forms from the s____ basic plan demonstrates adaptive radiation. Adaptive radiation produces organisms capable of exploiting different e________ niches; this gradual spreading out of the organisms is known as d________ evolution. Q. Although the mammalian fore-limbs are adapted for different functions, fundamentally their structures are the same (the same number of bones, muscles, nerves and blood vessels) and are just modifications of the pentadactyl limb (limb with five digits). This suggests that organisms possessing them have the same ancestry. The figure show forelimbs of different mammals, match the description and suggest the mode of life of the mammal possessing it, name an example for such a mammal: Special features Mode of life / example . Forearms of different mammals Evolution P.5 1. basic plan of pendadactyl limb composing of: Upper arm--humerus, forearm-radius & radius, wrist-carpels, and 5 digits with phalanges 2. long and extending finger bones, supporting a layer of skin between the digits 3. limb bones short and stout, extra phalanges to form a padde-like structure 4. radius and ulna fused for better support, Digits degenerated except one (the 3rd one) which become strong and extended, adding extra length to the limb. It is also hoofed so that it become standing on its nail’. 5. very stout and strong forelimb, shaped like a spade 6. long, flexible forelimb with grasping digits b) Analogous organs and Convergent evolution Organs of some animals perform the s____ function though their structures are fund_________ different. Such organs are said to be analogous. When different groups of animals adapt to the same habitat, they will develop characteristics that are more or less similar to solve the same pro_____ (under similar sel_______ pressure ). This phenomenon is known as c___________ evolution. For example the w____ of a bird and the wings of an insect are analogous organs which are adapted for flying but are fundamentally different. Similarly the fin of sharks and the forelimb of whale are analogous organs which are adapted for swimming. Evolution P.6 These are only dis______-related animals (though they are all vertebrates) which have mastered movement in a marine environment from different starting points. As a result their bodies, with a st__________ shape with fins or paddles, resemble each other in their outline and function, but are derived from fundamentally different structures. Structures which fulfil the same roles but have differing origins are called an structures. b) Vestigial organs Some organisms possess non-fun_______ organs which, in other organisms, have essential functions. Such organs are said to be vestigial. The greatly reduced c______ and ap_______ of man are useless but they are very big and have important functions in the rabbit. It is assumed that the caecum and appendix functioned normally in man's ancestor, but since then degenerated as man had changed from herb______ habit to omnivorous habit during the course of evolution. Whale and python have ve_______ hind limb girdles embedded in the body. It suggested that they were evolved from ancestors with functional hind limbs. Likewise, slugs have vestigial sh____ embedded in their dorsal surfaces. D) Comparative Anatomy of Embryos More evidence of common ancestry comes from study of the comparative anatomy of em_____. Embryologists have noticed that vertebrate embryos in the early stages of their development are difficult to tell apart. Related organisms go through s______ stages in their embryonic dev_________. The closer the relationship of groups of animals and plant through classification, the more do their embryos res_____ each other. Moreover, the arrangement of internal o____ such as the arteries and the structure of the developing h_____ in early vertebrate embryos also follow a very si____ pattern. All these similarities strongly suggest com ancestries. Evolution P.7 E) Evidence from Comparative Physiology and Biochemistry All living things have DNA as their genetic material, with a g______ code which is almost uni_______. The processes of reading the code and protein synthesis, using RNA and ribosomes, are very similar in prokaryotes and eukaryotes, too. Physiological processes such as respiration involve the same types of step and similar or identical biochemical reactions in all species. ATP is the universal e______ currency. Among autotrophic organisms, the biochemistry of photo__________ is virtually identical, as well. Thus biochemical analysis suggests a common o_____ for living things. The biochemical differences between the living things of today are limited. This makes it possible to measure the relatedness of different groups of organisms by the amount of the dif________ between specific molecules such as D___, p_______ and en______ systems. F) 'Genetic distance'- Differences between DNAs The phylogenetic relationship between related species can be studied by comparing their ____ using Rest______ Frag____ Length Polymorphisms (RFLPs). The use of RFLPs was first reported by Botstein et al. (1980) during their construction of a genetic linkage map in humans. RFLPs uses DNA re________ enzymes that recognize spe____ sequences in DNA: The restriction enzymes cleave the DNA at specific sites thereby creating frag____ of DNA. The fragments are then electrophoresed on a gel, hybridized and probed with a lab____ fragment of DNA. Similarity between samples is based on the either the presence or absence of similar mobility fragments (Botstein et al., 1980). Samples that differ genetically create different quant___ of fragments as well as different fragments of different l______. Genetic differences result in fragment differences as one or more base differences could result in a loss of cleav___ site or the formation of a new s___. Comparing DNA from a variety of living species can indicate quantitatively the degree of relatedness of their genes. The degree of relatedness of various primates to humans estimated in this way gives results as follows: chimpanzee (an ape) rhesus monkey vervet monkey galago (a prosimian) 97.6% 91.1% 84.2% 58.0% The result of genetic studies agrees very well with other evidence about the evolution of the Primates. b) The Composition of Key Proteins Another way of quantifying the degree to which species are related is to find the number of a_____ acid sequences they have in common in an essential protein such as cytochrome c or the protein of haemo______ which occurs widely in vertebrates. Variations in amino acid sequences of proteins arise from spontaneous m_______ in the genes that code for them. The more d_______-related two organisms are the more d________ they will show in protein composition, because more m_______ would have taken place over the geological time that separates them. Evolution P.8 It turns out that the sequences of amino acid residues of such proteins are similar in all living things in which they occur. Between the human and the chimpanzee, our nearest Primate relative, we have no differences in the amino acid sequence of our cytochromes and haemoglobin! When these results were used to construct evo_________ tree, the results are remarkably similar to that from comparative anatomy. Difference in amino acid sequence in haemoglobin between Human and other animals: Chinpanzee 0 Mouse 27 Gorilla 1 Kangaroo 38 Ape 2 Chicken 45 Rhesus monkey 8 Frog 67 Dog 15 Lamprey 125 Horse, cow 25 Sea slug 127 c) Immunological Evidence Immunology provides a method of detecting differences in p , and so quantifying relatedness of species. Human serum is used to induce the production of anti______ in a rabbit, and the product, Antihuman antibodies’ are obtained as a suspension. Ser__ from other animals may be tested against the Antihuman antidodies’. The more closely related the animal is to humans, the greater is the precipitation reaction that results. Taking the precipitate produced by human serum reacting with human antigens as 100 per cent, the following values indicate the percentage degree of evolutionary r__________: Animal chimpanzee, gorilla gibbon baboon spider monkey lemur hedgehog pig Group African ape Asian ape Old World monkey New World monkey Prosimian Insectivorous mammal Even-toed hoofed mammal % degree of relatedness 97 92 75 58 37 17 8 F) Evidence from Artificial Selection By sel______ those members of a species which showed a fav________ variation, such as increased size or improved flavour and artificially br_______ them by selective mating, selective propagation or pollination, the des_____ characteristics were perpetuated. Continued selective breeding by Man has produced the varieties of dom____ animals and plants of agricultural importance seen today. There are vast differences between present-day varieties and their ancestors. In terms of genetics. Man is preserving / s_________ those genes which are considered desirable and el________ those which are undesirable for his purposes. Evolution P.9 Whilst varieties of dogs. cats, birds, fish and flowers have been produced for sporting or decorative purposes. A recently developed form of artificial selection is the selection for res________ to antibiotics, pesticides and herbicides shown respectively by pathogens, pests and weeds. A vicious circle is produced as new strains of organisms become im_____ to the ever-increasing number of chemical substances produced to contain and control them. The principle of art______ selection is the same as nat_____ selection except that it is very much qui_____ and the features selected may not be of sur_____ value in natural populations. It is really a practical way of dem__________ selection in the evolution of species. Q. Would you expect the artificially selected & bred species to be successful if let to live in the wild ? Explain. G) Evidence from Classification If the species present on the earth were descended from a few simpler forms, then we could expect to be able to classify them into ph____, cl_____, or____, fa______, gen____ and species just as is now done. On the other hand, it is difficult to imagine how this would have been possible were the organisms not related by des____, but each specially created according to individual plans. The structural similarities between organisms which forms the basis of a nat_____system of phylogenetic classification, suggest the existence of an evolutionary process. These similarities and differences between organisms may be explained as the result of prog_______ adaptation by organisms within each taxonomic group to particular en____________ conditions over a very long period of t_____. IV) The Mechanism of Evolution Evolution by Natural Selection --- Darwin’s Theory Darwin's theory can be summarised into three observable f____ plus two ded_______. A) a) Over-reproduction (Observation 1) Organisms have enormous rep__________ pot_______, they often tend to increase in a geometric ratio. Evidences for such enormous reproductive potential include: The very slow-breeding elephant: if it were to bring forth six young in a lifetime, and if their descendants continued to breed at this rate, in 750 years there would be 19 million elephants. Many fish are capable of laying millions of eggs, e.g. female cod lays about 2-3 million eggs per year. Flowering plants generally produce many hundreds of seeds. b) Relative constancy of the numbers of species (Observation 2) Evolution P.10 Despite this tendency towards a geo_____ increase in numbers, the population of a given species tended to remain c_______. c) Struggle for existence (First deduction) d) Variation among the offspring (Observation 3) Among the offspring there are usually slight and perhaps hardly noticeable diff_______. Generally, no two offspring were i________. That is var_______ exist among offspring. e) Natural selection / survival of the fittest (Final deduction) Like produces l____. Those which survive to breed are likely to produce offspring si______ to themselves. The adv___________ characteristics which gave them the edge in the struggle for existence are likely to be inh______ on to the next generation. Individuals lacking favourable characteristics are less likely to survive long enough to breed. Over many generations their numbers will dec____. The individuals with fav________ characteristics will breed, with consequent in______ in their numbers. The inheritance of one small variation will NOT, by itself, produce a new species. However, the development and acc__________ of m____ sm____ diff__________ over many gen_________ might gradually lead to the appearance of a n___ species – one that has become so diff_____ that it cannot b_____ with the original stock of organisms. B) Darwin’s dilemma Darwin's chief difficulty was that he did not understand how organisms gen variations on which natural selection could act. It was generally accepted at that time that inheritance is blending, that is, some substance is passed from each parent to the offspring in which the two contributions mix and so the progeny would tend to be inter_______ in all characters (the so called paint-pot inheritance). Thus a red flower, crossed with a yellow flower, would sometimes produce orange offspring. This would lead to increasing uniformity within the species and not to the range of different characters required for natural selection to work upon. It was difficult to see how favourable variations could acc_________ if their effects were diluted constantly in this way. In an attempt to answer this problem Darwin proposed that envir_______ change could have brought about a spont______ production of new variations that could then be inh______--which is in effect another version of Inheritance of acq____ character’. Evolution P.11 Ironically, the solution to the apparent problem of replenishing variation was discovered in Darwin's lifetime although he was never aware of it; Mendel’s work which stated that the basic genetic factors are ‘part______, do not b____ and can reappear in subsequent generations’ could have account for the nature of var______ necessary for natural selection to occur. C) Neo-Darwinism This refers to a new interpretation of Darwin’s theory of natural selection in the light of modern g_____. It can be defined as: the theory of organic evolution by the natural selection of gen________ determined characteristics. Some definitions in population genetics : Population A population is a group of sexually reproducing organisms of the s____ species occupying a particular a____, the individuals in it share a com___ gene pool. Gene pool It is the sum total of all the genes within the reproductive cells of all the members of a pop________. Alleles frequency Natural selection It is the relative prop______ of the alleles of a gene present in a population. Evolutionary change A population whose gene pool shows consistent ch_____ from generation to generation is undergoing evolutionary changes. A process that determine allele frequencies in population through une_____ rates of reproduction of different phenotypes. The selection is done by the environment, thus all environmental factors act together to select which alleles are more adv_________ and adaptive in this particular environment The essential features of NeoDarwinism are : 1. Genes are responsible for determining our phenotypes. Phenotypic variation in the absence of g______ bases will not produce evolution. For variations to have significance in evolution, they must be her______ variation. 2. Source of genetic variation: Mut_____ is the ultimate s______ of all variation: it presents n__ possibilities to the organism. Sexual Recom_______ of alleles during meiosis (crossing over & independent segregation) and random fertilisation provides the immediate source of variation in sexual organisms. Mutant genes can be brought into the company of different alleles with which they will produce different phenotypic effects as a result of gene resh________. 3. Natural selection 'chooses' the b____-adapted organisms (that is, those with the most favourable collection of phenotypic characters) in a population to survive and breed more successfully than their less well-endowed competitors. 4. Individuals do NOT evolve, but p___________ do. 5. As a result of persistent natural s_________ forces acting on the g____ pool of a p__________, the gene fre_______ in the population might change. A population whose gene pool shows a consistent / directional change from generation to generation is undergoing evolutionary change. 6. Mechanism of speciation: Change in allele frequency within populations, as a result of effect of natural selection on the range of phenotypes produced by mutation and sexual reproduction, lead to the formation of r___ and sub_______. If genetic iso_____ persists over prolonged period of time, the subspecies might evolve in such different directions that they do not inter______ successfully again when they come together. Speciation is said to occur and the subspecies are then considered as separated sp______. Evolution P.12 D) Selection Selection is the process by which those individuals who appear phy_____, phy__________ and beh_________ better ad_____ to the environment sur____ and re_____; those organisms not so well adapted either fail to reproduce or die- i.e.be el________. The former organisms pass on their suc________ characteristics to the next generation, whereas the latter do not. Therefore selection can be seen to operate through the processes of differential mort____ and diff_______ reproduction. Selection depends upon the existence of phenotypic v________ within the pop_______. When a population increases in size, certain environmental factors become lim_____, such as food availability in animals and light in the case of plants. This produces com________ for resources between members of the population. Those organisms exhibiting characteristics which give them a competitive ad________ will obtain the resource, survive and reproduce. Both env___________ factors and pop_______ size operate together to produce a selection pres____. Which operate in a pop_________, increasing or decreasing the fre______ of an allele within the gene p____ of the population. Changes in al___ frequency in a l____ run can lead to evol_______ changes. Three Types of selection (Reference) There are three types of selection process occurring in natural and artificial populations and they are stabilising, directional and disruptive selection. They may be best explained in terms of the normal distribution curve associated with the continuous phenotypic variation found in natural populations. Evolution P.13 1) Stabilising selection This operates when phenotypic features coincide with st____ optimal environmental conditions and competition is not severe. The selection force tends to eliminate ext_____ from the population. Stabilising selection pressures do not promote evol________ change but tend to maintain phen_____ stab____ within the population from generation to generation. This is probably the most common way in which natural selection operates. Organisms which have lived for millions of years in very st____ environments closely resemble their ancient relatives. The oyster and the coelacanth fish are examples of creatures which have retained an almost constant form, presumably by the operation of stabilising selection. Q. Where do you suppose these living fossil’ would likely to be found? Search for information about one such organism and be ready to present your findings in the class (2 minute presentation). 2) Directional selection This form of selection operates in response to gr____ changes in environmental conditions. It exerts selection pressure which moves the m___ phenotype towards one phenotypic ext____. Once the mean phenotype coincides with the new optimum environmental conditions s_________ selection will take over. This kind of selection brings about evolutionary ch____ by producing a selection pressure which favours the increase in frequency of new alleles within the population. Directional selection forms the basis of art______ selection where the selective breeding of phenotypes showing desirable traits increases the fre_______ of those ph________ within the population. 3) Disruptive selection This is probably the rarest form of selection. Fluct______ conditions within an environment, say associated with season and climate, may favour the presence of more than one ph________ within a population. Selection pressures acting from within the population as a result of increased competition may push the phenotypes away from the population mean towards the ext______ of the population. This can spl__ a population into two subpopulations. If gene flow between the subpopulations is prevented, each population may give rise to a new species. In some cases this form of selection can give rise to the appearance of different phenotypes within a population, a phenomenon known as poly__________. Intensity of selection pressure External factors may include an increase in numbers of p______ or p_______ or competition from other species -i________ c_____________. Changes in c________ conditions etc. Internal factors such as a rapid increase in the size of the p_________ can result in increased competition for environmental resources - i___________ competition. Evolution P.14 One possible result of increased selection pressure is that it may cause organisms to become more sp________ to particular modes of life or narrower environmental conditions. This may be a disadvantage for the future of that species. Increased uniformity and dependency by a species increases the likelihood of that species becoming ex____ should environmental conditions change. The fossil record contains many extinct organisms that were bizarre and oversp________. E) Recent Examples of Evolution (by Natural Selection) in action There is no way we can prove natural selection was responsible for the evolutionary process that has taken place in the past. But examples of n_______ s________ in action are abundant all around us. a) Industrial melanism in moths The moth's wild-type colour is speckled grey (mottled form) which offers it good cam______ on a lichen-covered tree-trunk. Its chief pre______ are birds which hunt it by sight. An occasional m________ occurs which makes the moth very dark and conspicuous against a normal tree trunk. At the time of the Industrial Revolution, smoke-laden air began to kill l____ and deposit black films on city tree-trunks. Melanic moths show up less against sooty tree-trunks than do wild-type ones. The first recorded specimen of melanic Biston betularia occurred in 1848 in Manchester and, by 1895, about 98 per cent of the moths in that area were dark. Such an increase implies a powerful selective adv______ to the melanic form and illustrates how rapidly gene-fre_________ in a population can change under such circumstances. Predatory bird act as agent of n______ s________, favouring the survival of the best-cam________ moths. Where surfaces are blackened by soot the melanic form is better camouflaged and predation is largely restricted to the mottled form. In areas not polluted by soot the reverse is true and the mottled form predominates. There are more than 150 species of moths known to exhibit industrial melanism. Q. What kind of selection is shown in the case of the melanism in moth? (hint: think about the polymorphic form of moths that resulted) b) Metal tolerance in plants One of the most convincing examples of natural selection is provided by the evolution in certain grasses of tolerance to heavy metals, such as copper, zinc and lead. Various physiological mechanisms* have evolved to allow these plants to grow and reproduce in soils, e.g. spoil from mines, where heavy metals are present at concentrations that kill normal plants. Indeed, the plants have become so well adapted to living in such conditions that on unpolluted soil they do not fare so well and are out-comp____ by normal plants. Evolution P.15 *In some species the toxic metals bind to organic molecules in the cell walls where they remain trapped, unable to harm the cells. In other species the metals are stored in the vacuole. Other species trap the metals at special membrane sites. Some plants simply export the metals from their cells to the external environment. c) Insecticides The wide______ use of insecticides has provided a selection p________ which has resulted in adaptive changes within a very short time. It has taken only a few years, and in some cases only months, to produce strains of insects which have become completely re______ to many insecticides. The widespread use of DDT to control insect pests has lead to the evolution of re________ to this chemical by many species. One Nigerian survey of mosquitoes in the species Anopheles found that in unsprayed villages almost no flies were resistant to DDT. However in villages which had been subject to regular spraying, approximately 90 per cent of the flies were homozygous for resistant alleles. In house flies, several mechanisms are known which permit resistance. Four genes are involved and each has a distinct function. Two of the DDT-resistant genes enable the poison to be detoxified, each by a different route. Another gene reduces the rate at which DDT penetrates the cuticle. The fourth gene acts by an unknown route. d) Antibiotics The resistance of bacteria to antibiotics has arisen by the sel______ of resistant mutants. As with types of insecticide resistance, some resistance to antibiotics has evolved by 'switching on' genes to control the production of anti______-splitting enzymes. Resistance to antibiotics has already destroyed the usefulness of several drugs. The first signs of staphylococcal resistance appeared soon after penicillin became extensively used in hospitals. Resistance has now appeared in certain staphylococci to all major antibiotics, often as a triple resistance to penicillin, tetracycline, and streptomycin. Nowadays doctors tend to be more restrained than they were about how many different antibiotics they prescribe. That way, a few really effective ones can be kept in reserve to be used only if a bacterium is resistant to all the more common antibiotics. Q. Name three features of bacteria that enable them to evolve so quickly in response to selection pressure. Q. Antibiotic resistance is becoming a hot issue in HK. There are malpractices in both the medical practitioners and the patients that should be blamed. What are these malpractices? e) Adaptive immunity in mammals Micro-organisms and insects rep________ at such an alarming rate that it is relatively easy to visualize how they can adapt faster than man can combat them. Prolifically breeding mammals such as the brown rat and the rabbit have also evolved resistant strains capable of withstanding warfarin and myxomatosis virus, respectively. Warfarin was developed as a rat poison. It interferes with clotting in the blood. In 1960, strains were first recognized which were immune to warfarin. The incidence of resistant rats in parts of Wales had risen to 50% by 1970 because of the intensive selective pressure of the widespread use of warfarin. Myxomatosis-resistance in rabbits became widespread in the mid 1950s. Prior to this, the virus was responsible for up to 90% mortality of rabbits in certain areas. The genetic response to this selective pressure was the production of mutants which spent a greater proportion of time above the ground, like hares. Normal rabbits live in crowded warrens underground where the vector of the virus, the rabbit flea, can spread rapidly throughout a population. Those that spent most time above ground were favoured, whereas previously they were selected against because of predation. Even though the rabbits Evolution P.16 were not physiologically resistant, their altered behaviour offered them protection. In the Australian population, however, a genetically resistant strain emerged after the initial epidemics. Most British rabbits are now genetically resistant to myxomatosis. f) Sickle-cell anaemia This is caused by a mutation which resulted in the incorporation of an incorrect a____ acid at one point in the protein chains of the h__________ molecule. The mutated gene is known as Haemoglobin S or HbS and is recessive. Those persons homo_____ for the gene suffer acutely from the disease. The disease is an often fatal form of anaemia which is relatively common in West A____. Whenever the blood cells of a victim encounter a low level of oxygen, as in the venous blood of tissues, they are liable to collapse to a s____ shape and may form blockages and other complications in blood vessels. Sufferers have only a 20% chance of surviving to maturity as compared with normal people. Het_________ individuals suffer also, even though the symptom is milder. Given this information, one would NOT expect the mutation to be favoured. Indeed, such harmful mutations are frequently elim________. This happens rapidly where it is a dominant gene, more sl_____ where it is a recessive, as selection acts only when it appears in the ph_______. However, there are still large areas of Africa and Asia where the gene occurs, usually in the hetero_________ form in 15-20% of the population. There are even communities within these regions with frequencies of 40%. Clearly, the gene is not being removed from the population. The answer lies in resistance to mal___. Children with HbS have been shown to have a 25% better chance of surviving malarial attacks than those with normal genes. Selection is NOT acting to remove the genes causing sickle cell anaemia. They are removed when hom_______ but this selection is outweighed by their selective advantage when het_________, due to better resistance on the part of heterozygotes to malaria. Examples of natural selection in action are abundant. It is widely believed that over time natural selection has been the prime mechanism dri_____ evolution and is still oper_____ today. V) A) Speciation and Isolating Mechanisms The definition for a species The term pecies’ can be defined in different ways: In terms of classification, it is one of the smallest / lowest u___ of classification commonly used; members of the same species shared the greatest resem______ structurally and functionally. In terms of breeding & genetics, members of the same species are capable of inter_______ and produce fer___ offspring. Evolution P.17 B) Speciation This is the process by which one or more species ar___ from previously ex____ species. If speci_____ occurs whilst the populations are sep_____ it is termed allopatric speciation. If the process occurs whilst the populations are occupying the s____ geographical area it is called sympatric speciation. Allopatric speciation is characterised by the occurrence, at some stage, of spatial separation or geo________ sep_______. This inability of organisms or their gametes to meet leads to rep_______ isol______, which will in turn produce a bar____ to g___ flow and thus population become gen_______ isol____. i) Allopatric speciation Organisms belonging to a given species rarely exist naturally as a single large population. It is usual for a species to exist as small interbreeding populations, each with its own g___ pool. Spatial separation by geo_______ barriers such as mountain ranges, seas or rivers means that sp_____ separated pop_______ of the same species may encounter a vari___ of environmental conditions and different selection p_______. As a result of geo_______ barriers, gene f___ between populations might become interrupted. As a result of this each subpopulation becomes genetically is . The effects of natural sel_______ on the range of ph______ produced by mut_____ and sexual recom________ will result in changes in allele and genotype fre________ within the populations, this lead to the formation of r___ and subsp____. If the genetic isolation persists over a prolonged period of t____ and the subspecies then come together to occupy the same area they may or may not inter_____. If the breeding is successful they may still be considered to belong to the same species. If the breeding is unsuccessful, then sp________ has occurred and the subspecies may now be considered to be sep______ species. Q. An initial factor in the process of speciation may be the reduction in the intensity of selection pressure within the population. This may lead to increased variability. These new phenotypes may enable the population to increase its geographical range if the phenotypes show adaptations to environmental conditions. a. Under what circumstances would there be ‘reduction in the intensity of selection pressure in the environment ‘? b. What is the genetic basis of the origin of the ‘increased variability’ ? Evolution P.18 Sympatric speciation i) In complete contrast to allopatric speciation, species undergoing sym_____ speciation are NOT geographically isolated by, for example, a mountain or a river. The speciating populations share the same ter________. Sympatric spe_______ events are most common in p____ when they double or triple the number of chromosomes, resulting in a condition called p________. In such cases there might also be intraspecific speciation (auto_____________) or inter-specific speciation (allo____________). In the latter case it is also called interspecific hyb_________. Polyploidy results in an ‘Instant species’ in contrast to allopatric speciation which requires a much long period of t____. Sympatric spe_______ can also explained by disr______ selection which favours individuals at both ext_____ of a range of phenotypes over those in the middle. Thus the gene pool may become sp__ into two distinct gene p____. This may be a way in which n___ species are formed. An example of how disruptive selection might lead to sympatric speciation: Tolerance to heavy metal contaminated soil The residues of mines often contain high concentrations of toxic heavy metals (e.g., copper, lead) that most plants are unable to grow on them. However, some hardy species (e.g. certain grasses) are able to spread from the surrounding uncontaminated soil onto such wasteland. These plants develop resistance to the toxic metals while their ability to grow on uncontaminated soil decreases. Because grasses are wind pollinated, cross-breeding between the resistant and nonresistant populations goes on. But evidently, disruptive selection is at work. Higher death rates of both less resistant plants growing on contaminated soil and more resistant plants growing on uncontaminated soil leads to increasing divergence of the populations into two subpopulations with the extreme manifestations of this trait. Evolution P.19 In all cases, either allopatric or sympatric speciation will eventually lead to certain forms of rep_______ isolation and hence g_____ i______ of the subpopulations, in time increasing genetic diver______ of the g____ p___ of the sub_________ might lead to production of separate species. Reproductive Isolating mechanisms Speciation will only occur as a result of the formation of barriers which lead to reproductive isolation. This can be brought about by mechanisms acting before or after fertilisation: Prezygotic mechanisms (barriers to the formation of hybrids) Seasonal isolation Occurs in animals where differences in genitalia prevent successful copulation and in plants where related species of flowers are pollinated by different animals Ecological isolation Occurs where two species mate or flower at different times of the year. Behavioural isolation Occurs where two species inhabit similar regions but have different habitat preferences; for example Viola arvensis grows on calcareous soils whereas Viola tricolor prefers acid soils Mechanical isolation Occurs where animals exhibit courtship patterns, mating only results if the courtship display by one sex results in acceptance by the other sex; for example certain fish, bird and insect species Postzygotic mechanisms (barriers affecting hybrids) Hybrid inviabilit y Hybrids fail to produce functional gametes; for example the mule (2n = 63) results from the cross between the horse (Equus equus, 2n = 60) and the ass (Equus hemionus, 2n = 66) Hybrid sterility Hybrids are produced but fail to develop to maturity; for example hybrids formed between northern and southern races of the leopard frog (Rana pipiens) in North America One way in which allopolyploidy can produce an Instant’ species: Diploid 2n1 chrom osomes meiosis Diploid 2n2 chrom osomes meiosis Gamete n1 chromosome s Gamete n2 chromosome s Diploid hybrid n1 + n2 chromosom es Non-disjunction during asexual reproduction chromosomes cannot pair, therefore meiosis fails no Viable Gametes (sterile) Tetraploid hybrid 2n1 + 2n2 chromosomes chromosomes all find homologous partners Viable Gametes With n1 + n2 chromosomes (self-fertile) Evolution P.20 Why is polyploidy important? Polyploidy has long been recognized as a prominent force shaping the evolution of plants. Many important crop plants, such as alfalfa, cotton, potato, and wheat polyploids. Based on fossil records, 70% of angiosperms were estimated to have had a polyploidization event in their species’ history. Many polyploids are more vigorous than their diploid progenitors and both autoand allo-polyploids have built in mechanisms for maintaining high levels of heterozygosity. Thus polyploids may exhibit a phenomenon similar to hy_____ vigor, or heterosis. Polyploids also are known to exhibit new ph______ variation that can arise shortly after polyploid formation. Hybrid vigor, also known as het_____, is an agriculturally important phenomenon describing the observation that the hybrid offspring of two inbred genetically different varieties produces higher y_____ than either one of the two parental lines. Evolution P.21 G) Concept Map: Evolution and the proposed mechanisms of Evolution Key words : changes, generations, genotypes, gradual process, successive, population of organisms, Evolution is a in which undergo in over Reference reading I: Lamarck's theory of Evolution Lamarck published his theory of evolution in1809. His theory is developed from a series of postulates. The formation of a new organ in the body, is the result of a new need which has arisen and continues to be felt by the animal. The extent of development of organs and their power of action is proportional to their use. All changes in or acquisition to the bodily organization of an individual during its life are transmitted to its descendants by the process of reproduction. There is no evidence of inheritance of characters acquired during the life of an individual. The theory of Lamarck fails to give an adequate explanation of evolution because the postulates on which it is based cannot be accepted in the light of present knowledge. Evolution P.22 Reference reading II: Darwin, Wallace and the theory of Natural Selection A) Darwin, Wallace & Natural Selection Charles Darwin was born in 1809, the son of a doctor, and like many great people he had an undistinguished academic career. In 1831 he accepted an unpaid post as naturalist on the survey ship H.M.S. Beagle, which spent the next 5 years at sea along Coasts of S. America. The Beagle returned to Falmouth in October 1836 via the coast of Chile, the Galapagos Islands, Tahiti, New Zealand, Tasmania and South Africa. For most of this time Darwin was concerned with studying geology, but during a five-week stay on the Galapagos Islands he was struck by the similarities shown by the flora and fauna of the islands and mainland. In particular he was intrigued by the characteristic distributions of species of tortoises and finches. He collected a great deal of biological data concerned with variation between organisms which convinced him that species were not immutable. On his return home his work on the selective breeding of pigeons and other domestic animals gave him a clue to the concept of artificial selection. An earlier Essay on the Principles of population by the Reverend Thomas Malthus, published in 1778, had highlighted the consequences of the reproductive potential of Man. Darwin applied this to other organisms and saw that despite this the numbers within populations remained relatively constant. Having collated a vast amount of information he began to realise that under the intense competition of numbers in a population, any variations which favoured survival in a particular environment would increase that individual's ability to reproduce and leave fertile offspring. Less favourable variations would be at a disadvantage and organisms possessing them would therefore have their chances of successful reproduction decreased. These data provided Darwin with the framework to formulate, by 1839, a theory of evolution by natural selection, but he did not Publish his findings at that time. Indeed Darwin's greatest contribution to science was not so much to show that evolution occurs but how it might occur. In the meantime, Alfred Wallace, who had travelled widely in S. America, Malaya and the archipelago, , had come to the same conclusions as Darwin regarding natural selection. In 1858, Wallace wrote a 20-page essay outlining his theory and sent it to Darwin. This stimulated and encouraged Darwin and in July 1858, Darwin and Wallace presented papers on their ideas at a meeting of the Linnean Society in London. Over a year later, in November 1859, Darwin published On the Origin of species by Means of Natural Selection . All 1250 printed copies were sold on the day of publication and it is said that this book has been second only to the Bible in its impact on Man's thinking. During his voyages on the Beagle, Darwin visited the Galapagos Islands which are about 1000 km off the northwest coas t of South America. Darwin realised that the birds on the Galapagos Islands were different from those of the mainland. He counted 13 species of finch, and noticed that each had a slightly different shaped beak . Evolution P.23 a. In figure above, which beak is adapted to which food? b. Natural selection only partly explains why this adaptive radiation took place in the finches of the Galapagos. The geographical isolation mechanisms operating in the islands also played an important part in the evolution of the finch species. What main factors have contributed to the evolution of so many finch species in the Galapagos? c. The following statements relate to the diagrams in figure below. Write out the statements in the correct order and, beside each, put the letter of the diagram which corresponds to it. Corresponding diagram Event The finches increased in numbers and, under the influence of natural selection, gradually became adapted to the local environment. Some finches from the second island managed to fly back to the first island, but reproductive isolation had occurred between them and the existing population. Originally, there were no finches on the islands. Some finches from the mainland managed to fly across to them. Some of the finches managed to fly to a second island where the environment was different. This process was repeated over and over again as the finches colonised more and more of the islands. Adaptation to the conditions on the second island gradually took place. Correct order Reference reading III: A) Misconceptions about Darwin’s theory of Evolution 1. Darwin was the first to propose that Evolution occurred The idea of evolution can be traced to a thousand years before Darwin back to that of Aristotle time. The important contribution of Darwin is to propose a mechanism that explain how evolution might take place---namely by natural selection. 2. Darwin tried to explain how life originated on Earth. Darwin made no attempt to describe how life originated on Earth: his concern was how new species might arise from pre-existing species. 3. According to Darwin: “Man is descended from apes”. The statement implies the idea of ‘a linear progression of evolutionary event leading from apes to human being’ which is simply wrong. The correct interpretation of the evolutionary relationship between Man and apes is that man and apes probably have a common ancestry, just as we say we Chinese all originated from some common ancestry around the Huang river a very long time ago. Evolution P.24 B) Arguments against the theory of Natural Selection Opponents of the theory of evolution by natural selection (though not of the fact of evolution) make a number of criticisms: 1. Mutations are usually harmful, so it is impossible to conceive that random mutations could accumulate to the benefit of a species. 2. Whilst complex organs, such as the eye, function effectively, it is difficult to imagine how a halfevolved eye would be useful. (The theory of natural selection demands that each 'stage' in the evolution ofan organ must be beneficial in itself, without the need to propose a directive force which 'works towards' a distant end.) 3. The theory does not account for the evolution of the higher taxonomic categories (genus, family, order, class, phylum). These criticisms can be met as follows: 1. Since mutation is a rare event, organisms are heterozygous for a mutant gene when it first appears. Harmful effects can be suppressed if they are recessive, and natural selection therefore favours those organisms in which the mutant gene's phenotypic effects are minimal, until total recessiveness is achieved. All organisms carry a reservoir of potentially harmful mutant genes whose expression is limited or suppressed. The majority of these genes will have minor effects, since those with profoundly harmful attributes are likely to kill the organism before natural selection has the opportunity to modify their effects. Polygenic inheritance is particularly suited to subtle evolutionary change. Since a particular character is under the control of many genes, none of which has a very great effect, one mutation will not cause much phenotypic change. More likely, that character will merely appear a shade more extreme so that a gradual shift occurs as mutations accumulate. Such a process is much less likely to cause dramatic, harmful effects than the mutation of a 'major', non-polygenic gene. Suppressed mutant genes which are kept 'in reserve' may have effects which are beneficial under changed environmental circumstances. The genes conferring lead-tolerance to Agrostis tenuis appeared to 'served no useful purpose' until the grass encountered lead in its surroundings. 2. Complex organs develop their attributes gradually. A simple light-dark detector performs less well than a vertebrate compound eye, yet its possessor may survive better than a competitor without it. Improvements can be added gradually. The eye did not appear suddenly in the offspring of an eyeless creature; it is the result of an evolutionary development that took many millions of years. Amphioxus, a primitive fish-like form which has no eyes but light-sensitive pigment cells in the brain may have been the starting point. From this rudimentary beginning the eye has passed through innumberable stages, each slight change useful to its possessor, and therefore adjusted to the demands of the environment by natural selection. 3. The evolution of the higher taxonomic categories appears to require a different process from that of speciation. The discontinuities between the groups is wide; there are no organisms half-way between ferns and conifers or between butterflies and beetles. The problem lessens when we realise that existing plants and animals are a mere fraction of those types which have existed. The extinction of a group's relatives leaves it distinct and becoming more distinctive as it diversifies and specialises. Fossils fill some gaps, although even these represent a biased sample of past life. Most organisms were not suitable for fossilisation and the earliest ones have been destroyed by crushing and heat in the rocks. If every organism that has lived could be resurrected, the collection would be much more of a continuum than a collection of all living species. Life has evolved over the last several million years. In such a time-span, events become inevitable which would be highly improbable in the short-term. Evolutionists believe that evolution is a creative response of the living matter to the challenges of the environment. The role of the environment is to provide opportunities for the biological inventions. Evolution is due neither to chance nor to design; its is due to a natural creative process.’ Reference : http://www.talkorigins.org/origins/faqs-evolution.html http://evolution.berkeley.edu/evosite/misconceps/index.shtml Evolution P.25 C) Can Evolution be controlled by man The answer is 'Yes’ in certain circumstances.' The achievements of such control are most obvious in those species, such as cultivated c___ and dom_______ animals, which man has directly utilized for his own benefit and convenience; the possibilities are present in many other species; while the attempts are most uncertain and most controversial in man himself: Artificial Selection--Plant and animal breeding Man has been practising domestication of animals and plants since early human civilisation. The basis of artificial selection is the isolation of natural populations and the selective b_______ of organisms showing characteristics or traits which have some usefulness to Man. The selective forces operating might have been uncon____ effects such as protection offered by man from natural predators which will have relaxed selection pressures towards evasion mechanisms; or con_____ selection will have occurred towards such aims as increased grain yield in wheat or faster hunters among dogs. Over thousands of years these processes have produced large changes from the original forms and enormous div_____ among contemporary forms, as can be readily seen among dogs. In artificial selection Man is exerting a dir______ selection pressure which leads to changes in allele and genotype frequencies within the population. This is an evolutionary mechanism which gives rise to new breeds, strains, varieties, races and subspecies. There are two forms of artificial selection called inbreeding and outbreeding. 1) Inbreeding This involves selective reproduction between cl____ related organisms, for example between offspring produced by the same parents, in order to propagate particularly des_____ characteristics. The extreme form of inbreeding is s___-fertilization. Inbreeding is a particularly common practice in the breeding of 'show' animals such as cats and dogs. It was used by livestock breeders to produce cattle, pigs, poultry and sheep with high yields of milk, meat, eggs and wool respectively, but for reasons stated below inbreeding is not now widely practised . Prolonged inbreeding lead to a reduction in fert____ -- a particular problem in the breeding of livestock. Intensive inbreeding reduces the vari______ of the genome (the sum of all the alleles of the species) by increasing the number of homo______ genotypes at the expense of heterozygosity Implication of inbreeding in evolution Meiosis is ineffectual in generating variability Recombination is meaningless in an individual which is completely homozygous. The progeny are genetically un_____ and identical to the parent from which they derive. Variability is exposed Since there are no heterzygotes in the population, recessive alleles cannot be hid___ in the heterzygous form; They are exposed as homozygotes and acted upon by n______ selection immediately. Unfavourable ones are rem____ from the population. There is immediate fitness of the at the expense of flexibility, i.e it does not allow variation. All the inbreeding pure lines breed true and each produces progeny which are identical to one another and to their parents. If the parents are well adapted to their environment then all of the progeny are also well adapted and there is im______ fitness. There is no wastage due to variable genotypes which are not well adapted. In the short term, inbreeding may be adv_________, particularly where conditions are of an extreme kind. The disadvantage of inbreeding is that it lacks long term flex______ and makes no provision for the fut____. When the environment changes there is only a limited pool of var________ from which to draw, and if none of lines are viable in the new environment then they will all die. Without the regular release of variation in each generation, inbreeders have no capacity to adapt, and in evolutionary terms they have no future. Evolution P.26 2) Outbreeding i) Hybrid vigour resulting from outbreeding It involves crossing individuals from genetically distinct populations. Outbreeding usually takes place between members of different varieties or strains, and in certain plants between closely related species. The progeny are known as hy____, and have phenotypes showing characteristics which are sup to either of the parental stocks. This phenomenon is known as hybrid vi or heterosis. Hybrids produced from crossing homozygous parental stocks from different populations are called F1 hybrids and show advantages such as increased fr___ size and s___ number, increased re________ to disease and earlier maturity. Increased vigour results from the increased hetero -- which arises from gene mixing. e.g, whilst each homozygous parent may possess some, but not all, of the dominant alleles for vigorous growth, the heterozygote produced will carry all the dominant allele. Increased vigour can also result from new phen______ particular combinations of alleles in the heterozygote. due to interaction between ii) Implication of outbreeding for evolution Maintain heterozygosity and variabilty In natural populations of outbred species, there is a wide range of variations present among the individuals. Only some of them are well adapted to the prevailing environmental conditions. If there is a change in the environment, some of the variants may be better suited to the altered conditions. Future adaptability and long term flexibility Genetic systems based on outbreeding are therefore more flexible than those based on inbreeding, and make more provision for the future. Outbreeders are more adaptable and their capacity for change also means that they are able to survive under a greater variety of conditions iii) Example of animal breeding : Artificial insemination In farm animals, it is frequently used as a rapid means of spreading the beneficial characteristics of a particular male throughout the stock. It involves the collection of semen, its dilution and, if required, storage ror long period at very low temperatures. When required the Semen can then be injected into fenales to cause pregnancy. Using this technique, one male can be used to fertilize many more females than would be possible using natural mating; the semen can be stored even after the animal has died; and it can be sent over long distances so that the genetic material can be used as widely as possible. Artificial insemination is most widely used with cattle, particularly cows for milk production, but the technique is now becoming more common in pig breeding and can be used with almost any mammal. Q. the semen from a single bull can be used to sire as many as 90 000 cattle a year. With so large a number, why do you think it is extremely important for farmers to maintain accurate breeding records? iv) Reference Reading : Artificial selection in Human? Could the kind of artificial selection we have been discussing be imposed on humans? To most people this idea seems repugnant, conjuring up visions of selective breeding and compulsory birth control and eugenics. In fact it already happens to a slight degree as when, for example, a couple with a history of abnormality in their children or close relatives decide, perhaps on the basis of information given them by a genetic counsellor, not to have any more children. Recently, though, advances in molecular genetics, it is already possible to detect carriers for a recessive allele. Further, if in vitro fertilisation is accompanied by suitable biochemical tests carried out at the 8-16 cell stage, doctors may be able to determine whether the embryo will develop into a healthy baby or show any genetic abnormalities. This information could then be made available to the woman before a decision has to be taken as to whether or not to implant the embryo into her womb. To what extent genetic testing, particularly prenatal testing, be available to parents? Evolution P.27 VI) Evolution : A mixed-up A He believed species changed by the use or disuse of parts of the body. B this can be caused by mutation, meiosis or environmental influences. C Evolution, from a primitive type of organism to several divergent forms adapted to distinct modes of life. D The type of bird Darwin found many species of. E Selective breeding by man. A demonstration of evolution under the direction of human influence. F Geographical barrier to interbreeding. G The oldest fossils of vertebrates are these. H The birds on the island Darwin made famous showed many different varieties of this body part. I This prevents varieties of the same species breeding because they are in season at different times. J Factors preventing interbreeding. K A lizard-like fossil which has feathers. L A famous variety of moth which changed from pale to dark when their trees got covered in soot. M Grouping of different organisms. N The islands which Darwin made famous. O A famous naturalist spent five years on this boat. P These survive. Q Organisms' remains that are found in certain types of rock. R The type of rock in which ancient organisms can be found preserved. S When populations become this it can be because they feed and lay their eggs on different plants or breed at different times of year. T A group of organisms which can interbreed successfully. U The change in a population of a species over a large no. of generations. V The limbs of vertebrates have 5 fingers in common. W Can be caused by ultraviolet light or X-rays. X The process the moths (Clue L) went through when they changed colour. Y Adult vertebrae might be different but these remain similar in all vertebrates. Z Survival tests set by the environment. a Parts with the same purpose but different fundamendal structure. Organisms possession of these structures do not imply a close evolutionary relationship. It merely indicates adaptations to similar conditions. b Birds evolved from these animals. c Man who believed species changed genetically. d They believe in the origin of the species as described in the book of Genesis. ADAPTIVE RADIATION ANALOGOUS ARTIFICIAL SELECTION BEAGLE BEAK ARCHAEOPTERYX PEPPERED MOTH BREEDING BARRIERS CLASSIFICATION EMBRYOS EVOLUTION FINCHES FISH FITTEST FOSSILS FUNDAMENTALIS TS GALAPAGOS REPROODUCTIVEL Y ISOLATED LAMARCK MUTATION INDUSTRIAL MELANISM CHARLES DARWIN NATURAL SELECTION PENTADACTYL REPTILE SEDIMENTARY SPATIALLY ISOLATED SPECIES ECOLOGICAL BARRIER VARIATIONS The end !