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Emotion as a Central Role in Moral Actio...

gogol — Fri, 16 Oct 2009 15:24:34 +0200

Although Hume assigns a central role to emotion in moral action, he does not eliminate reason. "A very accurate reason or judgment is often requisite, to give the true determination, amidst such intricate doubts arising from obscure or opposite utilities.Professional Editing services for college and university people by talented editors " The moral person thus must possess a well-developed rational capacity in order to be capable of morally correct action. In regard to the emotions, Hume makes a distinction between calm and violent passions. The calm passions produce little emotion in the mind and are of two kinds: "either certain instincts originally implanted in our natures, such as benevolence and resentment, the love of life, and kindness to children; or the general appetite to good, and aversion to evil." The violent emotions include fear and jealousy. It is the calm passions, not the violent, that are at the heart of moral action. According to Hume, "What we call strength of mind, implies the prevalence of the calm passions above the violent." The Humean moral person would exhibit such strength of mind. What about the Humean woman? I believe it reasonable to suppose that Hume perceived woman's inferior strength of mind as affecting the degree to which she possessed the very qualities needed for moral action: a prevalence of the calm passions over the violent and an accurate judgment. Despite the fact that Hume wrote remarkably little about woman's nature, comments that support this conclusion can be found in Hume's writings. The most telling piece of evidence is Hume's claim that "the fair sex has a great share of the tender and amorous disposition." According to Hume, the amorous passion is not a calm passion, but one of "force and violence.If you need written term paper, order original custom paper writing assistance online! " Having defined the virtuous mind as one which "reduces the affections to a just moderation," Hume offers a number of warnings about the passions of love. Hume admonishes us to base our marriages on friendship rather than love, for "love is a restless and impatient passion, full of caprices and variations arising in a moment from a feature, from an air, from nothing, and suddenly extinguishing after the same manner." Furthermore, he tells us that the amorous passions, although agreeable, can "weaken and enfeeble" the mind. Thus one of the weaknesses of woman's mind, her susceptibility to the passions of love, an inferiority Hume perceives as innate, inhibits her ability to properly judge the utility of actions, and thus to act virtuously.

Hume’s View of Woman

gogol — Fri, 16 Oct 2009 15:21:22 +0200

In the essay, "On the Immortality of the Soul," Hume repeats his contention that woman's mental capacities are inferior to those of men. "The inferiority of women's capacity is easily accounted for. Their domestic life requires no higher faculties either of mind or body." Although this statement leaves one wondering whether Hume viewed women's intellectual and bodily inferiority as inherent or acquired, in others, such as the one cited above, there is no such ambiguity, in that Hume believes the difference to arise from nature. Talented written term paper are always online to assist you with essay writing; custom services! It appears that Hume subscribed to a position similar to that of Aristotle and quite in keeping with the European view of women in the eighteenth century: "civilized" woman is intellectually and physically inferior to "civilized" man, and her inferiority is innate. This interpretation receives further support from Hume discussion of justice in his Enquiry Concerning the Principles of Morals. Hume poses the question of one's obligations "were there a species of creatures intermingled with men, which, though rational, were possessed of such inferior strength, both of body and mind, that they were incapable of all resistance, and could never, upon the highest provocation, make us feel the effects of their resentment." His answer is that such creatures should be treated humanely, but that they possess no rights and our actions would not be governed by what Hume calls "the restraints of justice." He insists that this properly describes the relationship between men and nonhuman animals, but does not apply to the relationship between "civilized Europeans" and "barbarous Indians," nor between "civilized" men and "civilized" women. In the case of "civilized" women, Hume explains that although the male superiority in bodily strength is sufficient to maintain their tyranny over women, "such are the insinuation, address, and charms of their fair companions that women are commonly able to break the confederacy, and share with the other sex in all the rights and privileges of society." "Civilized" women, thus, are to be treated with equal justice, not because they show men the error of being so treated through reasoned arguments, or act to show men this error with such courage and resolution that men are able to feel the effects of women's resentment, but rather because of their charms. In A Treatise of Human Nature, Hume discusses a group of natural abilities--intelligence, good sense, judgment, wit, and eloquence--which he categorizes as virtues. All of these are mental qualities, and all are, on Hume's reckoning, innate. custom research paper - order custom research paper draft from scratch by experienced writers! Since these qualities are perceived as virtues by Hume, they are abilities we would expect to find well developed in the Humean moral person. In fact, Hume had earlier characterized Cleanthes as possessing both wit and knowledge and exhibiting fine judgment in treating all fairly.

Cleanthes “Model of Perfect Virtue” and...

gogol — Fri, 16 Oct 2009 15:20:31 +0200

Let us look more closely at Cleanthes, the "model of perfect virtue." We are told that Cleanthes is a man of honor and humanity who treats everyone fairly and with kindness. He is dedicated to his profession, which, in combination with his insight into the nature of people, promises "the greatest honours and advancement.custom written papers of academic quality is rare. Buy custom service, essay and paper writing, here! " He is sociable, witty, well-mannered, gallant, knowledgeable, and cheerful. He "preserves a perpetual serenity on his countenance, and tranquillity in his soul," for despite trials, misfortunes, and dangers, "his greatness of mind, was still superior to all of them." Hume makes the image of Cleanthes clearer by offering a list of vices he does not have: "celibacy, fasting, penance, mortification, self-denial, humility, silence, solitude, and the whole train of monkish virtues." These, Hume claims, serve no purpose, and in fact hinder an individual by stupefying the understanding and hardening the heart. The question before us is whether there is anything in Hume's moral theory which precludes a female Cleanthes. Hume remains relatively silent concerning the subject of women. However, he offers a discourse on the virtue of chastity in women and also offers scattered remarks concerning woman's nature. I will turn to these passages in an attempt to determine whether the Humean moral person is as likely to be a woman as a man. In his essay "On the Rise and Progress of the Arts and Sciences," Hume offers an aside on the topic of gallantry. Having discussed the Roman custom of honoring first the person of the greatest distinction, Hume refers to the modern notion of offering respect and deference to one's inferiors, what he calls "gallantry." Arguing against the Roman custom, Hume argues that modern gallantry is both generous and natural, in that it keeps us from causing injury to others and renders intercourse between people more agreeable. "A polite man," Hume tells us, "learns to behave with deference towards his companions, and to yield the superiority to them in all the common incidents of society." Hume then turns to the relations of the sexes, arguing that in this arena, gallantry is crucial. "As nature has given man the superiority above woman, by endowing him with greater strength both of mind and body, it is his part to alleviate that superiority, as much as possible, by the generosity of his behaviour, and by a studied deference and complaisance for all her inclinations and opinions.It is not difficult to Editing essay with the assistance of experienced paper editors! Make your essay error-free! " He argues that such gallantry is wise as well as generous, for without it women would be little other than the slaves of their husbands. "Barbarous nations display this superiority [i.e., of man over woman], by reducing their females to the most abject slavery." Hume explains that such conditions preclude all possibility of discourse, sympathy, friendship, and gaiety between the sexes. The natural affection between the sexes thus requires the gallantry of men in order to achieve its fullest satisfaction.

Humean Moral Person

gogol — Fri, 16 Oct 2009 15:19:38 +0200

Although retaining a division between reason and emotion, Hume reverses the Cartesian privileging of reason over emotion. "Reason is, and ought only to be the slave of the passions, and can never pretend to any other office than to serve and obey them.It is easy to Edit my essay with the advices of educated essay editors! Make your essay error-free! " The Humean moral person is the opposite of the Kantian dispassionate, disinterested, autonomous individual. Given his emphasis on emotion over reason, his attention to the moral importance of relationships between people, and the types of traits ascribed to the moral individual, I believe it fair to conclude that Humean moral theory is feminine, or perhaps more fairly that it is androgynous, with an emphasis on the feminine. In this sense, Hume's moral theory can be seen as more balanced than that of Kant. Whereas Kant excludes emotions from the moral realm, Hume recognizes the importance of a balance of reason and emotion. Whereas the characteristics of a Kantian moral individual are male, the Humean moral person blends female and male traits: is sympathetic but, fair, passionate yet reasonable. It would, however, be premature to conclude from this that the Humean moral person is not "gendered," that is, that Hume perceived women as just as capable of moral goodness as men. As we have seen, women have often been seen as incapable or as less capable than men of reason. Therefore, since Hume's moral individual must be capable of reason as well as emotion, it is not obvious that women will be viewed as possessing an identical capacity for moral development. However, the reverse is not the case for men. Men have not been viewed as incapable of emotion. Emotion, often perceived as an inferior faculty of the mind, has been traditionally credited to women and men alike. But reason, seen as a more developed faculty of the mind, has been attributed only to those individuals seen as most evolved or "civilized"--typically upper-class, European males. Thus the question remains, Is the Humean moral person "gendered"? If we look at Hume's discussion of the moral person, it is clear that he was envisioning a man. He tells us, for example, that "when we enumerate the good qualities of any person, we always mention those parts of his character, which render him a safe companion, an easy friend, a gentle master, an agreeable husband, or an indulgent father.If you seek custom written papers, order original custom paper writing help online! " Similarly, at the end of the Enquiry, Hume presents us with a man, Cleanthes, as his model of the moral individual. It is thus important to determine if his description of the moral individual as male is simply a symptom of the sex bias of Hume's culture which he unwittingly inscribed on his moral theory, or if there is an aspect of his moral theory which necessitates the exclusion of women from the moral realm. It is to this question I now turn.

External Anatomy

gogol — Tue, 05 Aug 2008 14:49:44 +0200

A typical organizational plan that integrates functions and their underlying structures is bilateral symmetry and cephalization. Bilateral symmetry refers to a body that can be divided through only one plane into mirror halves. Cephalization refers to the tendency to collect specific structures toward one end of an animal body, which structures, collectively, are called a head. These include various sense organs--eyes, ears, nose, or another olfactory organ--and the mouth. Let us now look at how both bilateral symmetry and cephalization are adapted to the life a consumer, and especially, a predator, leads.

A head is selectively advantageous for an organism that first searches out its food and then eats it. In most animals, it is that part of the body that first encounters the environment; thus, the head contains sense organs to inform the body where it is going and where the food is. Such organs are coordinated with the organs of locomotion through the nervous system. And obviously, for the above reasons, it will also include the organ of ingestion, the mouth and its associated parts. A head is adaptive over the range of habits shown by consumers, from herbivores to active carnivorous predators.

Bilateral symmetry makes adaptive good sense in much the same way. A freely moving consumer that knows up from down and right from left has an advantage in being oriented to its environment. The location of prey, orientation towards it, and controlled approach or pursuit is enhanced by bilateral symmetry. Appendages are seen as a further refinement of such a body. They add to the maneuverability and the feeding capabilities of the animal.

The Metazoa: Invertebrate Animals

gogol — Tue, 05 Aug 2008 14:49:04 +0200

Invertebrate animals range in size from microscopic worms, free-living and symbiotic, to huge forms such as huge giant squids, which, including their longest tentacles, can be as much as 20 m in length. Within this size range, the variety of forms derives from a combination of various appendages attached to bodies that may or may not be segmented, but that are usually bilaterally symmetrical. Colors range throughout the possible spectrum and are combined in sometimes extraordinary ways. The invertebrates include insects and snails, star-fish and corals, and worms of all kinds--in all, about a million different species. And all of them are consumers.

The term predator is usually reserved for animals that hunt their prey. A lion preys on zebras and antelopes, an octopus often preys on crabs, many spiders prey on insects, and so on. We do not think of zebras or antelopes as preying on grass; nor do crabs that browse on algae or butterflies that obtain nectar from flowers strike us as predators. Nonetheless, in all these cases, a similar function is carried out; this includes locating, and orienting to food, attaining it by capture or simply moving up to it (to graze, for example), and then ingesting it. Predators are simply the most dramatic example of this set of common coordinated behaviors. And underlying these behaviors is a set of common structural features. Notably, there is a nervous system for sensing and coordinating; a muscular systemfor moving, which also demands some sort of skeleton for muscle attachment and for transforming muscular action into mechanical action. And these are all integrated with a functional mouth for ingestion.

Fungal Phylogeny

gogol — Tue, 05 Aug 2008 14:48:47 +0200

The fungi still present many unsolved phylogenetic problems. There is wide agreement that they are polyphyletic; that is, that there are as many plesiomorphs as there are independently originated groups of fungi. It also means that the evolutionary trends within this kingdom are complex. Polyphylesis of the fungi. In a phenetic approach, thefungi were classified into four divisions, i.e., Phycomycetes, Ascomycetes, Basidiomycetes, and Fungi Imperfecti. These divisions largely depended on reproductive structures, with the last being a catch-all for forms whose reproductive structures (and, therefore, life cycles) were unknown. This approach did not satisfy those who felt that classification should be more than just a way to store and retrieve information, i.e., that it should also reflect evolutionary history.

We see here that the Phycomycetes are missing, and in their place are three other divisions. These are thought to be close to monophyletic groupings. The Fungi Imperfecti, now designated Deutoromycota, are accepted as probably having no sexual reproduction; they reproduce asexually by spore-formation and elongation of hyphae. Then three unusual groups are placed here, but there is no real conviction that they are genuine fungi. The first of these are the lichens. There are 15,000 to 20,000 species of these organisms, which represent symbiotic relation between a fungus and an alga and show identifying features from the blue-green and green algae and from the Basidiomycota, Ascomycota, and Deuteromycota. Obviously, classification and evolutionary relations are difficult beyond the recognition that their status is special and that they are arbitrarily put in with the fungi. The other two groups are the cellular slime molds and the plasmodial slime molds, which seem to have independent origins. Both have a sporeforming stage that is fungal in appearance, which is now believed to represent convergent evolution. Both have an ameboid stage in their fife cycle, during which feeding is by phagocytosis. In this stage their character is clearly that ofunicellular ingestor or animal, which strongly indicates a protozoan nature. In fact, many schemes of protozoan classification include the slime molds. They are included here only because they are commonly classified among the fungi; it is an Adansonian solution to their taxonomic status, not an evolutionary one.

There remains the two major divisions of the Ascomycota and Basidiomycota. These, plus the former Phycomycophyta, are often combined into one division as the Eumycophyta or true fungi. It is within this grouping that phylogenetic trends, if they can be studied anywhere in the fungi, are most apparent.

Fungal Diversity

gogol — Tue, 05 Aug 2008 14:48:27 +0200

The second major group of multicellular organisms, the kingdom Fungi, is usefully discussed now, since it too arose in all probability from the protistan protophyta. But whereas the Metaphyta arose from photosynthetic forms, the Fungi arose from non-synthetic ancestors. The Fungi are eukaryotic and predominantly multicellular decomposers, with diverse types of organization.

The bodies of these organisms are sometimes unicellular, but more often organized into filaments. Each filament is called a hypha; collectively, they make up a mycelium. The mycelium, which may be highly branching, extends into the environment that nourishes the fungus. Typically, as decomposers, the fungi live in moist areas where there is an abundance of organic material. Hence their occurrence in dead wood or the litter on forest floors. But they also invade animal tissues--athlete's foot is caused by a fungus. They are severe problems in terms of food spoilage, since they cause molding of breads and vegetables, but they are also helpful in food production, especially in beer brewing and wine making, which depend on the fermentation of yeasts, and in certain cheeses. The colored patches in blue cheese are the result of fungal growth. In brief, fungi grow just about anywhere there is organic material that can be decomposed. Decomposition occurs through the release of enzymes that degrade substrates in the immediate vicinity of the hypha. These substrates are macromolecular constituents produced by other organisms because such molecules contain necessary building blocks for further growth of the fungi. Proteins supply amino acids, nucleic acids nucleotides, and carbohydrates and lipids sugars and other carbon compounds. These smaller molecules are assimilated into the fungal cells and used there for vegetative growth.

Reproductive functions involve sexual reproduction as well as asexual spore-formation. Although the reproductive structures of the familiar puffballs, mushrooms, toadstools, and brackets of shelf fungi are rather complex structures, they constitute the lesser part of fungal growth. The usually invisible mycelium comprises the mass of the organism and is quite simply organized. Only in the reproductive structures does complexity approach that seen in the thalli of the red or the brown algae, for example.

The Origin of Mosses and Liverworts

gogol — Tue, 05 Aug 2008 14:46:48 +0200

Phylogenetically, these known nonvascular plants are off on an evolutionary side branch, quite distinct from the other metaphytan species. The reasons for this are their lack of vascular tissue and the dependence of their sporophyte generation on their gametophytic one. Thus, although there are useful homologies between the green algae and these bryophytes as regards pigments, photosynthetic products, and cell walls, the course of evolution from the ancestral algae was probably independent of that taken by Rhynia and other vascular plants. This could even mean--and it is not unlikely--that land habitats were successfully invaded at least twice by descendents of the green algae. And these two invasions were based on two different kinds of adaptations, notably descendents with and without vascular tissues and their associated patterns of alternation of generations. But again there is a gap. The transitional forms between the green algae and ancestral mosses and liverworts are not in evidence today any more than are those forms between the green algae and vascular plants.

It may be that these gaps can be narrowed, if not closed, by demonstrating conservative or plesiosemic molecular characters. Molecular evolution might reveal changes that indicate important homologies between multicellular green algae and plesiomorphic vascular and nonvascular plants. Of course, a fossil plant like Rhynia will have few proteins in which amino acids can be sequenced, but the lycopods may turn out to be quite informative.

Why and How Would a Welladapted Aquatic...

gogol — Tue, 05 Aug 2008 14:46:29 +0200

The answer seems to lie in the realization that for freshwater algae--the green algae are the most common freshwater forms--their habitat, when it consists of shallow ponds or streams, often, and even annually, dries out. Adaptations for surviving desiccation would be advantageous, and such adaptations would be preadaptations for living on land. When we consider the evolution of green algae in such terms, it is not improbable that terrestrial forms evolved. But we have no fossil evidence or other data to document that evolutionary breakthrough. There is a gap. It could well be another case of tachytelic evolution, wherein a form adapted to one adaptive zone invades a new zone, evolutionary changes are rapid, and no fossils are found. Furthermore the intermediates are not really successful aquatic plants nor are they successful land plants. They lose out in competition to both. Hence, no intermediates survive. But we cannot, from present information, document Lignier's hypothesis.

This again illustrates the frustrations of phylogenetic research: the concept of evolution encourages us to look for phyletic series, but the action of natural selection tells us we must both expect and accept gaps. Perhaps the most disconcerting aspect of such a gap is our lack of insight into how the primitive transport tissue--the stele--of Rhynia arose. It is disconcerting for two reasons. First, despite the relative simplicity of the rhyniophyte stele (it is a thin strand of long, slender cells in the middle of the stem), it makes a rather sud-den or genuinely neosemic appearance. It cannot be homologized with any green algae cells. Such apparently sudden and discontinuous changes, as we have emphasized, are inconsistent with the known process of evolutionary change. We can only hope that new data from living or fossil plants that represent a useful missing fink here will become available. The second reason is the origin of the nonvascular plants.

The Flowering Plants

gogol — Tue, 05 Aug 2008 14:46:08 +0200

The emergence of the flowering plants is still something of a mystery. Darwin, in 1879, wrote his botanist friend Hooker that "the rapid development so far as we can judge of all the higher plants within recent geological time is an abominable mystery. I would like to see the whole problem solved." Seeds emerged as a further development of sporangia, for example, appearing within the cones of the conifers. Then seeds appeared within the flower. But where did the flowers come from? A possible candidate for the plesiomorph of flowering plants is a magnolia such as Magnolia soulangeana. As with all plesiomorphs, it shows a series of characters that are conservative and therefore representative of the ancestral condition, although a magnolia plant as a whole is not consistently a conservative plant. The actual ancestor of the flowering plant has not been found in the fossil record, and efforts are still being made to reconstruct it. In terms of the flower, which is the critical feature here, we see a structure still bearing parts highly suggestive of evolution from a twig.

A long fascinating story can be summarized by looking at some of the trends in floral evolution. This story tells us that flowers underwent an adaptive radiation and in some cases, reverted to pollination by wind, which probably occurred in the ancestral plants from which they somehow evolved. We say somehow because Darwin's "abominable mystery" is still with us. Statistical analyses, such as that by Kenneth Spome, of the University of Cambridge, England, can tellus that a plausible ancestor for the flowering plants is the curious group of plants known as the cycads. They are not conifers, but members of a group that seems to have had a parallel, but somewhat independent evolution. But that still begs the question of how they arose. That must be answered in selectionist terms. Something about the flowering plants gave them a survival advantage over other plants. A recent approach to this question is that of Philip Regal, of the University of Minnesota. He starts at an obvious point, i.e., the flower. This feature of these plants is obviously unique and neosernic, and it would not exist unless it had a selective advantage. Other angiosperm features can be found to one degree or another in other seed plants. These include broad leaves, substances that repel predators, and vessels instead of theA recent approach to this question is that of Philip Regal, of the University of Minnesota. He starts at an obvious point, i.e., the flower. This feature of these plants is obviously unique and neosernic, and it would not exist unless it had a selective advantage. Other angiosperm features can be found to one degree or another in other seed plants. These include broad leaves, substances that repel predators, and vessels instead of theregarding the evolution of the vascular plants. Quite clearly, Lignier is looking for aposemic changes connecting an aquatic green alga to a plant that is adaptive to the land.

Asteroxylon

gogol — Tue, 05 Aug 2008 14:45:41 +0200

Asteroxylon shows stem-like structures that clearly look as if they extended into the soil. In the club mosses we see genuine roots. They have the specialized structures and associated functions characteristic of roots. Some place in the line of evolution between Asteroxylon and Lycopodium, real root structures evolved. This appears neosemic because we look at the ends of the series, i.e., forms without true roots and then forms with roots.

The tracheids of the vascular tissue were evolving throughout this sequence, going from annular through helical and scalariform to ones with bordered pits and, eventually, to vessels. Rhynia has annular tracheids. Asteroxylon has helical ones; the lycopods and some ferns have scalariform ones; bordered pits are frequent in seed plants; and vessels characterize flowering plants. Furthermore, it is important to know that in the embryonic development of plants, annular, helical, and scalariform tracheids can all appear, and in that order. It is clearly a case of an evolutionary history persisting in the development of an individual. In the nineteenth century, Ernst Haeckel pronounced this to be the Biogenetic Law. As we said earlier, further work has shown many exceptions to this "law," but here, in tracheid development, is one of its more obvious manifestations.

Also regarding vascular tissues, there is convincing aposemic evidence in the changes shown by the organization of the xylem and phloem, the significance of pith, etc. These details cannot be covered, here, but are amply documented in texts that cover plant anatomy and its evolution. (See references at the end of this chapter.) Finally, it can be noted that certain flowering plants, such as certain cacti, entirely lack vessels. This is another case of simplification through reduction and loss.

Last, we consider the evolution of gametophyte and sporo-phyte stages. In the sporangia of the lycopods there is a gametophyte stage, but whether gametophytes occur in Asteroxylon, Sawdonia, and Rhynia is still conjectural. That is, although there is every reason to believe they occurred in those plants, they have not as yet been identified. A different problem is the two different patterns of occurrence of gametophytes and sporophytes in the ferns and club mosses. In the ferns, there is a separate plant for each stage; in the club mosses, the gametophyte develops within the sporophyte, as it does in the seed plants. In ferns the situation appears to be a dead end--it has gone no further than what we see. The ferns are an example of homosporous plants, i.e., plants that produce only one type of spore. This spore germinates into a gametophyte with male gametes in its antheridia and female gametes in its archegonia.

Rhynia and the Subsequent Evolution of V...

gogol — Tue, 05 Aug 2008 14:45:25 +0200

Ideally, in a careful phylogenetic analysis, we want to find the actual plants that serve as intermediates between Rhynia and present-day vascular plants. This would fulfill the serial relationship and indirectly establish homologies between Rhynia and such plants as the ferns, conifers, and flowering plants described above. More specifically, we need to show the evolutionary development of roots and leaves. These would be neosemic traits, since both are absent in Rhynia. When both arise, they would then develop aposemically to reach the stages seen in the ferns and the seed plants. Since a stem with a stele is already present in Rhynia, we must look for its aposemic development into forms with more complex tracheids and leaf traces before we reach the level of organization manifested by ferns and seed plants. Similarly, we want to see how sporophytes and gametophytes evolved, aposemically.

Starting with roots and leaves, we find a truly useful series of forms intermediate to Rhynia and other vascular plants. In this series, it should be emphasized, we are in all probability not looking at a series of direct descendants of one plant from the other, but at plants specialized in their own right and representing side branches from some main line of evolution that produced today's vascular plants. These intermediates mark the general direction of evolutionary change, rather than being actual forms that arose sequentially one from the other. Admittedly, though, fossil forms are the most likely place to find them. This series going from Rhynia through Sawdonia, Asteroxylon, to the club mosses or lycopods, is a remarkably complete documentation of neosemic innovation and aposemic changes subsequent to it.

In terms of leaves, Sawdonia has pointed extrusions on its stem, but they are not connected to vascular tissues; hence, they are not true leaves. In Asteroxylon, the lateral extensions of the vascular strands look like leaf traces. They extend from the central stele toward the leaflike scales. And then, in present-day club mosses of the genus Lycopodium, we see true vascularization of the scale-like growths on the stem; they are leaves.

Roots emerged gradually from prostrate stems into struc-tures adapted to root functions, i.e., uptake of water and nutrients, and anchoring of plants. Though we referred to the root as a neosemic structure--it is absent in Rhynia and present in all seed plants--it apparently emerged by the gradual transformation of stem-like parts.

It is worth noting that no structure or function emerges suddenly. Evolution proceeds by the slow accumulation of advantageous mutational changes. Complex structures and their functions are the result of many such changes (thousands or more) and to expect that they would occur simultaneously andproduce a new functional part of an organism that is adaptively significant, is so improbable as to be dismissed. Rather, a slow accumulation of changes, each one beneficial in terms of survival, is the tactic used by evolution. Sometimes complex structures having one function can change their function, and thus selection for one function becomes a preadaptation for another.

Metaphytan Algal

gogol — Tue, 05 Aug 2008 14:45:04 +0200

The two metaphytan algal phyla have separate origins. What about the rest of the Metaphyta, the multicellular terrestrial plants? Again, from information given earlier, we see good evidence for homologies in the pigments, photosynthetic products, and cell walls of these plants and the green algae (Chlorophycophyta). The problem now comes down to locating a plesiomorph for the land plants and then seeing if it can be homologized to any of the multicellular, aquatic green algae.

One outstanding candidate for the plesiomorph of the vascular land plants is Rhynia gywnne-vaughani. This is a fossil plant of the Silurian and Devonian periods of the Paleozoic (about 400 × 106 years ago). This plant is described by paleobotanists as a leafless, rootless, branching stem. Part of the stem was prostrate on the ground and from it there extended tufts of slender filaments--not roots--into the ground. Presumably they took up water and minerals. The aerial part of the plant had only one specialized structure at the end of some of the stems, interpreted as sporangia, for the formation of spores. Within the sporangia are the expected tetrads of cells, a characteristic of spores. These structures identify the plant as a sporophyte. Stomata are seen on the stems and this suggests that the stems were photosynthetic. Furthermore, the fossils are so well preserved that a very simple vascular bundle, or stele, can be identified in the center of the stem. Tracheids of the stele are even identifiable as annular. They make up the xylem, and surrounding it is the recognizable phloem.

Except for such plants as the duckweed Lemna, no other vascular plant is as simply organized as Rhynia. In the case of Lemna, there is every reason to think of its simplicity as being due to a reduction of parts from much more complex plants.

Now Rhynia as a plesiomorph poses at least three problems: (1) How did more complex vascular plants, with roots and leaves and gametophyte as well as sporophyte stages, arise from it? (2) What was ancestral to Rhynia? (3) Rhynia maywell be the plesiomorph for the vascular plants, but what about a plesiomorph for the nonvascular mosses and liverworts?

Metaphytan Plesiomorphs

gogol — Tue, 05 Aug 2008 14:44:47 +0200

The ancestor of the metaphytans must have been eukaryotic, multicellular, photosynthetic, and aquatic. The first three characters are the most conservative or plesiosemic ones we can find in this kingdom. And the last character, though aposemic, since the metaphytans occur in marine and freshwaters as well as on land, is plesiosemic among those forms arguably close to ancestral forms. The multicellular algae are the plants that come most quickly to mind in response to these four requirements for metaphytan ancestry. What can we say about the red, the brown, and certain green algae in this regard?

The algae are not especially closely related. First, regarding the red algae, their lack of any motile cells and unique photosynthetic pigments place them closer to the prokaryotic blue-green algae than to the eukaryotes. It is thought that the red algae arose from the bluegreen algae; either through endosymbiosis or through transformation of a prokaryotic alga into a eukaryotic red algae. The problem here is much the same as for the origin of the protistans, in particular, the origin of the green algae. The plesiomorph of the red algae would have a relatively simple thallus and a simple fife cycle. A possible candidate might be Porphyra perforator. It must be emphasized, however, that there is a large gap--the gap separating prokaryotes and eukaryotes--between this red alga and the blue-green algae.

Turning next to the brown algae, we have a very difficult problem. These organisms suggest some similarity to the protistan golden algae (Chrysophycophyta). But there is no series of homologous semes that allows a convincing ancestor-descendant relationship to be established between the brown and the golden algae. There is a gap here; not as large as that between prokaryotes and eukaryotes, but nonetheless large. The first aspect of the problem is that there is no good candidate for a plesiomorph for the brown algae. All the brown algae are multicellular and have fairly complex to very complex life cycles. It is as if all the simpler ones have lost out by competition to the highly evolved ones. The result is that forms suggestive of the ancestral form are missing. The second problem is that we do not find any multicellular protists in the golden or other algaethat show convincing homologies with the brown algae. The photosynthetic pigments of the Phaeophycophyta, Chrysophycophyta, and Pyrrophycophyta are somewhat alike, but only in a general way. Photosynthetic products, cell wall chemistry, occurrence of flagella, and patterns of multicellular organization are not arguably homologous. We do not really know yet what to say about the ancestor and origin of the brown algae except that the origin was probably from the Protista and that the ancestor and its related forms are extinct.