The Evolution of the First Tetrapods

Its one of the iconic images of evolution: 400 or so million years ago, way back in the prehistoric mists of geologic time, a brave fish crawls laboriously out of the water and onto land, representing the first wave of a vertebrate invasion that leads to dinosaurs, mammals, and human beings. Logically speaking, of course, we dont owe any more thanks to the first tetrapod (Greek for four feet) than we do to the first bacterium or the first sponge, but something about this plucky critter still tugs at our heartstrings. As is so often the case, this romantic image doesnt quite match up with evolutionary reality. Between 350 and 400 million years ago, various prehistoric fish crawled out of the water at various times, making it nearly impossible to identify the direct ancestor of modern vertebrates. In fact, many of the most celebrated early tetrapods had seven or eight digits at the end of each limb and, because modern animals adhere strictly to the five-toed body plan, that means these tetrapods represented an evolutionary dead end from the perspective of the prehistoric amphibians that followed them. Origins The earliest tetrapods evolved from lobe-finned fishes, which differed in important ways from ray-finned fishes. While ray-finned fishes are the most common type of fish in the ocean  today, the only lobe-finned fish on the planet are lungfish and coelacanths, the latter of which were thought to have gone extinct tens of millions of years ago until a live specimen turned up in 1938. The bottom fins of lobe-finned fishes are arranged in pairs and supported by internal bones—the necessary conditions for these fins to evolve into primitive legs. Lobe-finned fishes of the Devonian period were already able to breathe air, when necessary, via spiracles in their skulls. Experts differ about the environmental pressures  that prompted lobe-finned fish to evolve into walking, breathing tetrapods, but one theory is that the shallow lakes and rivers these fish lived in were subject to drought, favoring species that could survive in dry conditions. Another theory has it that the earliest tetrapods were literally chased out of the water by bigger fish—dry land harbored an abundance of insect and plant food, and a marked absence of dangerous predators. Any lobe-finned fish that blundered onto land would have found itself in a veritable paradise. In evolutionary terms, its hard to distinguish between the most advanced lobe-finned fish and the most primitive tetrapods. Three important genera nearer the fish end of the spectrum were Eusthenopteron, Panderichthys, and Osteolopis, which spent all of their time in the water yet had latent tetrapod characteristics. Until recently, these tetrapod ancestors nearly all hailed from fossil deposits in the northern Atlantic, but the discovery of Gogonasus in Australia has put the kibosh on the theory that land-dwelling animals originated in the northern hemisphere. Early Tetrapods and Fishapods Scientists once agreed that the earliest true tetrapods dated from about 385 to 380 million years ago. That has all changed with the recent discovery of tetrapod track marks in Poland that date to 397 million years ago, which would effectively dial back the evolutionary calendar by 12 million years. If confirmed, this discovery will prompt some revision in the evolutionary consensus. As you can see, tetrapod evolution is far from written in stone—tetrapods evolved numerous times, in different places. Still, there are a few early tetrapod species that are regarded as more-or-less definitive by experts. The most important of these is Tiktaalik, which is thought to have been perched midway between the tetrapod-like lobe-finned fishes and the later, true tetrapods. Tiktaalik was blessed with the primitive equivalent of wrists—which may have helped it to prop itself up on its stubby front fins along the edges of shallow lakes—as well as a true neck, providing it with much-needed flexibility and mobility during its quick jaunts onto dry land. Because of its mix of tetrapod and fish characteristics, Tiktaalik is often referred to as a fishapod, a name that is also sometimes applied to advanced lobe-finned fish like Eusthenopteron and Panderichthys. Another important fishapod was Ichthyostega, which lived about five million years after Tiktaalik and achieved similarly respectable sizes—about five feet long and 50 pounds. True Tetrapods Until the recent discovery of Tiktaalik, the most famous of all the early tetrapods was Acanthostega, which dated to about 365 million years ago. This slender creature had relatively well-developed limbs, as well as such fishy features as a lateral sensory line running along the length of its body. Other, similar tetrapods of this general time and place included Hynerpeton, Tulerpeton, and Ventastega. Paleontologists once believed that these late Devonian tetrapods spent significant amounts of their time on dry land, but they are now thought to have been primarily or even totally aquatic, only using their legs and primitive breathing apparatuses when absolutely necessary. The most significant finding about these tetrapods was the number of digits on their front and hind limbs: anywhere from 6 to 8, a strong indication that they couldnt have been the ancestors of later five-toed tetrapods and their mammalian, avian, and reptilian descendants. Romers Gap Theres a 20-million-year-long stretch of time in the early Carboniferous period that has yielded very few vertebrate fossils. Known as Romers Gap, this blank period in the fossil record has been used to support Creationist doubt in the theory of evolution, but it is easily explainable by the fact that fossils only form in very special conditions. Romers Gap particularly affects our knowledge of tetrapod evolution because, when we pick up the story 20 million years later (about 340 million years ago), there is a profusion of tetrapod species that can be grouped into different families, some coming very close to being true amphibians. Among the notable post-gap tetrapods are the tiny Casineria, which had five-toed feet; the eel-like Greererpeton, which may already have de-evolved from its more land-oriented tetrapod ancestors; and the salamander-like Eucritta melanolimnetes, otherwise known as the creature from the Black Lagoon, from Scotland. The diversity of later tetrapods is evidence that a lot must have happened, evolution-wise, during Romers Gap. Fortunately, we have been able to fill in some of the blanks of Romers Gap in recent years. The skeleton of Pederpes was discovered in 1971 and, three decades later, further investigation by tetrapod expert Jennifer Clack dated it smack to the middle of Romers Gap. Significantly, Pederpes had forward-facing feet with five toes and a narrow skull, characteristics seen in later amphibians, reptiles, and mammals. A similar species active during Romers Gap was the large-tailed Whatcheeria, which seems to have spent most of its time in the water.

Victim from Birth Deaf Essay - 833 Words

Eng 1a 5-23-13 Essay #1 In the article â€Å"Victims from birth† Wendy McElroy, ifeminists.com, is about Sharon Duchesneau and her deaf son named Gauvin. Duchesneau, being a lesbian, selected a sperm donor(along with her partner Candace McCullough). Duchesneau and McCullough are also deaf. The donor they selected was based on his family history of deafness to insure their son Gauvin would also be deaf. Duchesneau goes on to say that Gauvin â€Å"is not profoundly deaf†¦ but deaf enough† (McElroy 1). Gauvin was born with slight ability hear to. Gauvin would be able to hear well enough to perform normal functions with help from a hearing aid. However, Duchesneau and McCullough made the decision not to supply a hearing aide for their son. McElroy†¦show more content†¦Gauvin’s ability to make friends will be hindered the most. The majority of people do not know sign language and will have a hard time getting to know Gauvin. Being deaf, Gauvin will not go through the normal process of communicating with kids his age. While Gauvin is young, he will be limited in finding friends. Consequently, affecting his social skills. When he can communicate, he will not have the same social skills as hearing children his age. This correlates with finding somebody Gauvin can spend his life with. Being deaf affects Gauvin from being able to communicate with most girls. By the time Gauvin will be interested in a partner his social skills will not be as inept as people his age. Gauvin should have been granted a hearing aid in order to live an easier life. Not having this aid hinders his ability to learn, limiting his education options. Consequently, this will effect Gauvin on his search for a career. Most importantly, being deaf will do the greatest damage to his social life, changing the way he communicates with people. 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Evolution of the Genus Homo Free Essays

Evolution of the genus Homo. Charles Darwin was the first to formulate a scientific argument for the theory of evolution by Natural Selection. The idea of natural selection is basically â€Å"the survival of the fittest. We will write a custom essay sample on Evolution of the Genus Homo or any similar topic only for you Order Now † Evolution is any change in characteristics in biological populations. It gives diversity to life on all known biological organizations such as molecules, organs, organisms, etc. Life is said to be originated from a universal common ancestor, which tells us that all life is related to each other. Life started from simple celled organisms known as prokaryotes, which evolved into eukaryotes after photosynthesizing bacteria evolved forcing oxygen concentration to rise in the atmospheric. This event known as the Great Oxidation Event acted as poison on many bacteria that use carbon dioxide as an energy source. After the evolution of eukaryotes, sexual reproduction appeared and increased the evolution rate tremendously. Complex multi-cellular organisms started to appear soon after, first in oceans and then on land. Over time, life diversified into millions of organisms. The genus Homo first evolved around 2. 5 Ma from Australopithecine genus (now extinct). The first homo species believed to evolve were called Homo Habilis. They lived side by side with another homo species called Homo erectus until at least 1. 44 Ma. H. Habilis were also the first species to make tools out of stone. H. Erectus resembled modern humans and colonized in Africa. They had a brain size 74% that of modern humans and had ways of making better tools and also hunted bigger animals. Another species, Homo Antecessors were common ancestors of humans and H. Neanderthals. Modern humans shared 99% of their DNA with Neanderthals and Neanderthals also had a similar gene linked to speech. Another species, Homo Heidelbergensis may be an ancestor of Neanderthals and modern humans. Finally, modern humans or Homo Sapiens are said to first appeared around 200 Ka around Oma river, Ethiopia. There are two famous models that explain where the modern day humans originated from. Both models are supported by evidence and therefore are accept by different scientists. The Replacement model says that modern humans originated in Africa and replaced all other archaic humans beginning 60,000 years ago. The regional continuity model argues that all modern human evolved more or less simultaneously in all major parts of old world from local archaic humans. It is believed that environmental variables, along with natural adaption, such as pathogens, diet, survival needs, climate, etc. caused the different phenotypic diversity among human populations thus complicating the puzzle of modern human evolution. How to cite Evolution of the Genus Homo, Essay examples

Issues in Accounting Theory

Question: Discuss about the Issues in Accounting Theory ? Answer : Introduction The recent assignment intends to offer a detailed description of the selected articleHalf a Defence of Positive Accounting Research. The article centres on the positive accounting in the great sense of the research program, which aims to develop casual human behaviour descriptions within the accounting structure devoid of profit after tax within accounting. Moreover, the huge positivist research initiative has lot of deficiencies in reality. Several complexities those are inherent encompass the casual generation of the speculative models for being weathered, increased reliance on the hypothesis testing and decreased attention on the parameters numerical values. Summary of the Article Within this article, the researcher has intended to explore the positive approach related with the accounting research. Dorminey et al. (2016, pp. 20-55) stated that the accounting research of the positive approach is associated with wider intellectual project of scientific study that intends to evaluate the cause-impact association. Such deficiencies within positive research study are explained through choosing several sample papers that majorly consisted of auditing literature researches. It was gathered that positive research is recently used in counting and it is several loopholes in attaining the scientific objectives after selecting the sample researches for adjust with the objectives of the research. Moreover, the elaboration of Kuhn associated with normal science associates well with the accountings positive research. The prospects are described in details for Kuhnian crisis and revolution that can attain constructive accounting to attain its potential. The researcher elaborated Poppers criterion in order to demonstrate that induction is not adequate for gauging the correctness of a specific theory. Additionally, the article provided with a brief review on the theories of positive accounting misrepresentation. For elaborating the same, four classes of elaborations has been presented that encompass internal impacts, error measurements, relativity theory inefficiency and external effects (Ballwieser et al. 2012). For this reason, the researcher has observed that a particular theory cannot remain anecdotal by observations, however, it might select between more than two theories. Moreover, the decisive observations are deemed to falsify improper theories and it is only present in situation of support of a particular opposing theory. The article has also explained a detailed weakness and logic dissection is linked withstatistical testing of hypothesis. Moreover, it is revealed that it is deemed extremely dilute version of the Propper logic. This is because the test out of 20 might be rejected incorrectly at the 5% significance level (Bromwich 2016, p. 219). Moreover, the technical concern associated with testing of hypothesis in test statistic distribution considered within null hypothesis. Moreover, even if the technical issue cannot be resolved, there can be increased probability that the hypothesis testing might fail. This is present at the time only a particular alternative hypothesis is considered devoid of careful specification. Research Hypothesis/Question The mentioned research hypothesis has been developed for investigating the validity of positive accounting research: H0: The universe exists and this is beyond an individuals level of imagination. H1: Every event in the world have many reasons that develops a part of the universe itself H2: The individuals those are normal might gain highly reliable information regarding the international events with the support of cautious observation H3: The objective of the intellectual property is to employ observations in order to gain an international knowledge of the universe, particularly causation For testing the first hypothesis, several examples of the positive research in the accounting has been presented. As per Bromwich and Scapens (2016, pp. 1-9) the conduction of rational self-interest among ample parties those communicated with express or implied contracts. This has resulted in theorising the accounting procedures. For testing the third hypothesis, the researcher has considered explaining scientific ontology along with epistemology that signifies that the positive accounting research is not identical with accounting research. In contrast,Chatfield and Vangermeersch (2014) stated that events do not take place as the output of intervention or randomly from the outer universe. For evaluating the third hypothesis, the researcher has explained misrepresentation and hypothesis testing for validity determination. For this reason, as per the provided theory careful observation is needed by means of which preliminary ideas can be generated. As per the formal theory can be gener ated with testable anticipations, that is aligned with the remaining dependent and important empirical evidence. The anticipations of the new theory can be tested in accordance to the fresh observations in certain situations within which the fresh and the old theories make severalanticipations. In order to test the final hypothesis, several models must be tested with particular focus on dimension. Considering the same,Colasse and Durand (2014, p. 41) indicated that the mental models might be employed to develop the casual procedures taking place in the universe. For this reason, the researcher has prepared the above hypothesis that inadequately flowed in the literature review section. Theoretical Framework The below mentioned theoretical structures have been employed within this article in order to address the objectives of the research. Examples of positive research within accounting: The operation of the self-interest balance among the parties serves as the outcome by means of expressed or implied contracts in several types of organizations. This signifies the accounting selections impact on organizations managers, price and exposure decisions taken by the auditors, the regulators decisions with reference to standard setting and the academics professional devices. It is deemed important that in order to determine the information types that the investor employs for investment decisions (Henderson et al. 2015). This indicates that human beings nature is rational. Moreover, after the investigating of numerous accounting researchers, the accounting settings is analyzed devoid of coherent behavior such as the method by which audit professionals make several judgments and the manner in which managers employ discretion within performance evaluation systems (Crawfordand Lepine2013, pp. 32-48). Considering the same, the ins tances intend to identify that the positive research is higher than positive accounting theory. Scientific ontology and epistemology: According to Dyckman and Zeff (2015, pp. 511-524) epistemology, serves as scientific field that intends to explain several approaches assessable to obtain an understanding of the world. On the other hand, ontology intends to discover the activities and their link with answering the question. The human agency along with socially prepared roles, associations and practices, which signifies that social universe, acts as an objective sustenance devoid of the activities that does not need presenting ample rational reasons. Moreover, the universe might not be observed other than the human beings experiences and the participants explanations. For this reason, because of the epistemological and ontological difficulties, the objective is to attain a great knowledge of the causes of the accounting technique serves as futile exercise. Requirements of an efficient positive research program: From the selected article, it was gathered that a continuous testing of complex models those require careful analysis of variable measurements. Moreover, analytical modeling is deemed important for formulating and testing theoretical models. In order to employ the analytical modeling in the positive accounting techniques, previous occupation is necessary for transforming from traceability to plausibility (Peirson et al. 2015).The researcher has made sure that increased focus on measurement is needed, devoid of just testing. It is observed that a bias is associated with the accounting hat has a strong publication against dimension other than considering that the same is related with theory. Relevance and Drawbacks of the Article After the analysis of the mentioned article, it has been gathered that the study has signified a wide gap between the recent practices on the positive accounting and should consider making important contributions to the wider intellectual program (Guthrie and Parker 2016, pp. 2-10). In certain circumstances, there is lack of system optimization that is vital to be modified for correcting a particular mistake. Moreover, the article offers a rational approach of the scientific research that is validated through participating within accounting groups. With the support of the current research, it has been gathered that there is a requirement for effective theoretical models those are extremely dependable in nature. Moreover, such article has explained that positive accounting research is an implication of the quantitative models those are decreased to the statements of the anticipated trends between both the variables (Deegan2016). In contrast to that, a vital drawback that is revealed from the article is that such research might not result in human behavior awareness within the accounting context. This is for the reason that it is devoid of gathering of real life information collected from several sources. This particular drawback is being acknowledged in this article (Gaffikin and Aitken 2014). Conversely, the absence of the gathering of primary and secondary data has affected the research quality. In addition, the researcher conducted ample inferences based on several authors statements explaining positive research accounting. Finally, the quantitative elements are not offered superior importance that is vital in the recent years for anticipating the upcoming growth pg the company in the extended term. Conclusion The recent assignment intended to analyze the epistemology and ontology of the affirmative accounting research in order to ascertain its loopholes along with the techniques by means of which these loopholes can be addressed. It was gathered that the quantitative segments of accounting must be prioritized in order to determine the upcoming organizational performance. For this reason, it might be inferred that very less modifications within the program of positive accounting is needed to decrease the errors from companies in consideration to accounting. Reference List Ballwieser, W., Bamberg, G., Beckmann, M. J., Bester, H., Blickle, M., Ewert, R. and Gaynor, M., 2012.Agency theory, information, and incentives. Springer Science Business Media. Bromwich, M. 2016. The contributions of AC Littleton to accounting thought and practice.Memorial Articles for 20th Century American Accounting Leaders,49, p. 219. Bromwich, M. and Scapens, R. W., 2016. Management Accounting Research: 25 years on.Management Accounting Research,31, pp. 1-9. Chatfield, M. and Vangermeersch, R., 2014.The History of Accounting (RLE Accounting): An International Encylopedia. Routledge. Colasse, B. and Durand, R., 2014. 3 French accounting theorists of the twentieth century.Twentieth Century Accounting Thinkers (RLE Accounting), p. 41. Crawford, E. R. and Lepine, J. A., 2013. A configural theory of team processes: Accounting for the structure of taskwork and teamwork.Academy of Management Review,38(1), pp. 32-48. Deegan, C., 2016. Twenty five years of social and environmental accounting research within Critical Perspectives of Accounting: Hits, misses and ways forward.Critical Perspectives on Accounting. Dorminey, J. W., Hassell, J. M. and Rebele, J. E., 2016. Accounting education literature review (2015).Journal of Accounting Education,35, pp. 20-55. Dyckman, T. R. and Zeff, S. A., 2015. Accounting Research: Past, Present, and Future.Abacus,51(4), pp. 511-524. Gaffikin, M. and Aitken, M., 2014.The Development of Accounting Theory (RLE Accounting): Significant Contributors to Accounting Thought in the 20th Century. Routledge. Guthrie, J. and Parker, L. D., 2016. Whither the accounting profession, accountants and accounting researchers? Commentary and projections.Accounting, Auditing Accountability Journal,29(1), pp. 2-10. Peirson, G., Herbohn, K. and Howieson, B., 2015.Issues in financial accounting. Pearson Higher Education AU.