Analysis of One-step Self-etch Adhesive Systems

Analysis of One-step Self-etch Adhesive Systems Abstract: Purpose: To evaluate the performance of two types of one-step self-etch adhesive systems and one type of two-step etch-and-rinse (as a control) by examining the resin-dentin interface and assessing the nano-leakage. Materials and Methods: Cervical class V cavities were prepared in 30 sound human premolars. Two types of one-step self-etch adhesive, G-Bond (GB) and Adper Prompt L-Pop(APL), and one type of two-step etch-and-rinse adhesive, Excite (Ex), were used to bond the composite restorations. The restored teeth were incubated in water at 37ÂÂ ±1 oC for 24 h. Fifteen were subjected to further immersion in 50% ammoniacal silver nitrate solution for 24 h and soaked in photo-developing solution for 8 h. All teeth were sectioned across the bonding surface in bucco-lingual direction. The cut surfaces were polished, followed by 6N HCL application for 45s. All surfaces were metal coated before conducting the ultra-morphological observation, using the Field Emission Scanning Electron Microscope (FE-SEM), to characterize the hybrid layer and evaluate the nanoleakage. Results: A significant difference in the thickness of the hybrid layer was evident between all adhesive systems (ANOVA, p Conclusion: GB provides a nano-interaction layer at the dentin/adhesive interface that seems to play an important role in minimizing the degree of associated nanoleakage. Keywords:Â  Dentin adhesive, interface characterization, nano-leakag, one-step adhesives Introduction Although gap-free margins at the dentin/restoration interface could be achieved with some adhesive systems utilizing the total-etch technique, Sano et al., have described another pattern of leakage, by observing the penetration of silver nitrate along gap-free margins by the aid of either scanning (SEM) or transmission electron microscopy (TEM). Since leakage was found to occur within the nanometer-sized spaces around the collagen fibrils within the hybrid layer, it has been termed nano-leakage[1-5]. The nano-leakage usually represents permeation laterally through the hybrid layer and could be the result of the incomplete infiltration of adhesive resin into the demineralized dentin[3]. This kind of leakage may also allow the penetration of bacterial products or oral fluids along the interface, which may result in hydrolytic breakdown of either the adhesive resin or collagen within the hybrid layer, thereby compromising the stability of the resin-dentin bond[5]. In spite of the technique-associated difficulties, previous studies indicated the efficiency of 50% silver nitrate solution in detecting nano-leakage within the hybrid layer[3,6,7]. However, the acidity of that solution (pH = 3.4-4.5), during long time immersion could induce demineralization around the edges of the restorations, particularly into the partially-demineralized dentin, leading to false positive results[7-9]. The modified silver-staining technique was recently suggested to overcome the drawback of silver nitrate solution. It utilizes 50 wt% ammoniacal silver nitrate having pH measured at 9.5 aiming to eliminate the possibility of dentin dissolution at the hybrid layer[10]. Although the nano-leakage for various adhesive systems and its influence on bond strength have been evaluated in previous studies[11,12]. As well as the effect of different parameters as thermo-cycling and etching time on nano-leakage, this in vitro study aimed to evaluate the thickness of the interaction layer and nano-leakage of 2 types of one-step adhesive systems and one type of two-step etch-and-rinse (as a control)[8,13]. The null hypothesis tested was that the one-step adhesive system (G-Bond) might offer better adhesion to cavity walls via formation of a nano-interaction zone instead of the traditional hybrid layer. Materials and Methods Thirty sound freshly extracted premolars of patients indicated for orthodontic treatment were collected. The collected teeth were cleaned using the Pro-sonic 300 MTH (Sultan Chemists, Englewood, NJ, USA), and examined to ensure the absence of cracks using a binocular microscope at 20x magnification (Olympus Co., Tokyo, Japan). The selected teeth were stored in deionized water that contained antibacterial agent (0.2% sodium azide) for a maximum of 1 month[14]. Using No. 330 bur (Brasseler USA, Savannah, GA, USA) at high speed with copious air/water spray, standardized 2 mm deep class V cavities were prepared at the buccal surfaces 0.5 mm coronal to the cement-enamel junction of all teeth. The prepared margins were all placed in enamel. A metal, buccal-fitted, index was used to guide the external cavity outlines and a rubber stopper hanged to the burs shank has aided in determining the accurate cavity depth. All the prepared cavities were thoroughly rinsed with water and air-dried before receiving the composite restorations. Table1.shows the description and manufacturers of materials used in this study. Two one-step, self-etch (G-Bond); and (Adper Prompt L-Pop) adhesive systems were used to retain the Tetric Ceram hybrid composite restorations. In addition, 1 two-step, etch-and-rinse (Excite) adhesive system was also selected to serve as control (n= 10 cavities for each). The self-etch adhesive systems were applied to the prepared cavities and left for 10s before air thinning. Curing of both self-etching adhesives was performed by the use of a light-curing device (Hawe-Neos, Gentilino, Switzerland) for 10s. The dentin surfaces of control cavities were etched with 37% phosphoric acid (Ivoclar-Vivadent) for 15s, washed under copious air-water spray, then the excess water was removed by blotting with a tissue paper leaving the dentin visibly moist. The Excite adhesive was then applied using a brush for 10s and light-cured for 20s after air-drying of the excess material. The cavities were then filled with composite, and cured for 40s before finishing using 1000-grit abrasive paper (SAIT AC Abrasive, Torino, Italy) in presence of water-cooling. The restored teeth were incubated in distilled water at 37ÂÂ ±1ÂÂ °C for 24 h before sectioning and testing have taken place. Assessing the dentin/adhesive interface Five premolars from each group were half-sectioned bucco-lingually across the bonding surface with a low-speed diamond saw (model 650, South Bay Technology Inc., CA, USA). The cut surfaces were then lightly finished using a sequence of 600, 800, and 1000-grit abrasive papers (SAITAC Abrasive) in presence of water-cooling followed with light polishing with diamond paste. The samples were then immersed in 6N (mol/L) HCL for 45 seconds then rinsed with distilled water and dried for 24 h at 37ÂÂ °C (Binder Incubator, Type B28, Tuttlingen, Germany). The dried samples were sputter coated with gold-palladium (JEOL, JFC, 1100e, Tokyo, Japan.) The dentin/adhesive interface of each sample was then examined using a field emission scanning electron microscope (FE-SEM) at 30 KV (JEOL, JSM, 5600LV, Tokyo, Japan)[14]. The thickness of interaction layer was measured in micrometer using a standard microscale calibrated FE-SEM Evaluating the nano-leakage The root apices of the remaining five teeth of each group were covered with sticky wax (Dentsply DeTrey, Bois Colombes, France), while their entire surfaces were coated with two layers of nail varnish except for the cervical margin of the restored cavity and 1 mm around. A modified silver staining technique, was used with basic 50wt% ammoniacal silver nitrate (pH=9.5)[15]. The chemical reagents from which the staining solution was prepared are listed in (table 1). The solution was freshly prepared by dissolving 25 g of silver nitrate crystals in 25 ml of distilled water. Concentrated (28%) ammonium hydroxide was used to titrate the black solution until it became clear as ammonium ions complexed the silver into diamine silver ([Ag(NH3)2]+) ions. This solution was diluted to 50 ml with distilled water to achieve a 50wt% solution. The teeth were immediately immersed into the freshly-prepared ammoniacal silver nitrate solution in total darkness for 24 h, followed by thorough rinsing with running distilled water for 5 min. The stained teeth were then placed in a photo developing solution for 8 h under fluorescent light to reduce the diamine silver ions into metallic silver grains within the voids along the bonded interfaces[2,3]. After removal from the developing solution, the teeth were placed under running distilled water for 5 more minutes. The stained teeth were then sectioned and their cut surfaces were finished, polished and acid-treated foll owing the previously mentioned conditions. The measurements of silver penetration were calculated directly on the SEM monitor, using a multi-point measuring device, observing all the internal cavity margin lengths, in steps of approximately 100 ÂÂ µm[6]. The leakage values were expressed as the sum of the cavity margin lengths showing silver deposition. A comparison between these lengths among the three adhesive systems was possible since the dimensions of all cavities were standardized as mentioned before. Statistical analysis The data were statistically analyzed using SPSS statistical package version 10. The data were examined for normal distribution using Kolmogorov-Smirnov test. One way analysis of variance ANOVA was used to compare the values of the three groups. The Tukeys post hoc analysis was used to confirm the significance of differences detected between the test groups and the control. The test was considered significant when p Results SEM images representing the adhesive/dentin (A/D) interfaces (Fig 1-3) revealed a variation in the thickness of the detected interaction layers between the tested adhesive systems. ANOVA indicated significant differences between thickness of interaction layers of tested adhesives (p These differences were confirmed among the mean values of Ex and GB (Tukeys comparison, p Penetration of silver along the cavity walls was observed in all samples. (Fig.4-6). Table 3 summarizes the results of nanoleakage testing. ANOVA indicated significant differences between the mean values of the sum of the cavity margin lengths showing silver deposition in the tested adhesive systems (p Discussion Fear of bacterial ingress at the restoration/tooth interface and the subsequent caries recurrence has pushed the interest of researchers to assess the adaptation and adhesion of restorative materials against tooth cavity walls. Several studies, had the concern to evaluate the source of adhesive-dentin bond through assessing the interface characterization[2,16,17]. In vitro study, it is evident that the G-Bond created a thinner interaction zone in comparison to those formed with other adhesives (Figs1-3). Both the Ex and APL formed traditional hybrid layers as a result of resin infiltration within the demineralized dentin through the collagen fibrils. However, the demineralization in case of Ex seems to be more deep as a result of longer time of acid contact (30s). This assumption could explain the formation of the thicker hybrid layer[17] [17]. The interface formed by GB looks different as the surface of dentin is decalcified only slightly and there is almost no exposure of collagen fibrils. This suggest that functional monomers contained in the bonding material react with hydroxyapatite to form insoluble calcium, forming a thin transitional zone that could be measured in nanometers, so it could be termed a nano-interaction zone with the ability to reduce the risk of bond deterioration[18,19]. Moreover, evaluating the microleakage and recently the nanoleakage represent important means of assessing the defective adaptation of materials[20]. Although the use of silver nitrate dye was effective in detecting the nanoleakage, this in vitro study used the ammoniacal silver nitrate dye because of its efficiency doing the same job and to eliminate the drawback of the regular silver nitrate deminerlizing the dentin[3,4,10,15]. SEM images (Figures 4-6) indicated the presence of nanoleakage in all samples bonded with different systems as manifested by the infiltration of silver ions at the adhesive/dentine interface and in some instances around the collagen fibrils. These findings could be attributed to the effect of resin contraction at the time of its polymerization[21]. In addition, the improper wetting of the resin to dentin and collagen surfaces could exist as a result of the wet nature of dentin tissues and bonding resin viscosity[22]. The previously nominated factors could create nanogaps between the bonding resin and dentin surfaces. Confirming the same assumption, other researchers have related the occurrence of nanolekage to the presence of areas of imperfect resin infiltration, retained water or other solvent, poor polymerization, or phase separation[22,23]. On the other hand, various degrees of silver penetration and brightness were evident between samples of different groups indicating different degrees of nanoleakage. This result could be related to the chemical nature of the adhesive systems themselves that is reflected on the expected degree of polymerization shrinkage and the degree of water sorption (dye solution). The recently-marketed adhesive system, G-Bond, includes water and organic solvents in its chemical formula to improve resin infiltration within the wet dentin substrate, as well as nanofiller particles to reduce the extent of polymerization contraction[24]. A study by Pashley EL et al., stated that when HEMA is included as a polymerizable solvent for resin monomers, residual water may persist during evaporation as a result of lowering the vapor pressure of water by HEMA[25]. In previously published TEM observations, pure polymerized HEMA permitted extensive silver impregnation. The authors stated that when HEMA is copolymerized with other resin monomers in the presence of water, it could form hydrogel in the hybrid layer, resulting in additional silver filled patterns in the interfacial layer. In the present study, both APL and Ex. contain HEMA and water which could be the reason of the higher degree of nanoleakage. However the presence of alcohol solvent in the Ex formulation could improve the resin infiltration and accordingly reduces the degree of nanoleakage in comparison to the solvent-free adhesive APL[22,26]. Conclusion Within the limitation of this study, the hypothesis that G-Bond adhesive system can offer better adhesion to cavity walls is acceptable. The formation of a nano-interaction layer seems to play an important role in minimizing the degree of nanoleakage at the bonding interface Clinical relevance: Using the G-Bond adhesive system for bonding composite restorations can minimize the expected degree of nanoleakage and accordingly could reduce the possibility of the future caries recurrence. Figures: Fig (1): SEM image of the interface bonded with G-Bond. The area shown by arrows, between the cured adhesive layer (A) and the dentin (D), is the very thin interaction (hybrid) layer. The electron density in this area is higher than that found with other adhesives. C= composite resin, A= adhesive; D= dentin Fig (2): SEM image of the interface bonded with Adper Prompt L-Pop. The area shown by arrows, between the cured adhesive layer (A) and the dentin (D), is distinct (hybrid) layer with a uniform thickness than that with G-Bond. The funnel shaped configuration of the resin tags is visible, which is resulted by removal of the highly mineralized peri-tubular dentin. C= composite resin, A= adhesive; D= dentin Fig (3) SEM image of the interface bonded with Excite. The area shown by arrows, between the cured adhesive layer (A) and the dentin (D), is distinct (hybrid) layer with a uniform thickness than that with G-Bond. The funnel shaped configuration of the resin tags is visible, which is resulted by removal of the highly mineralized peri-tubular dentin. C= composite resin, A= adhesive; D= dentin Fig (4): SEM image of the interface bonded with G-Bond showing minimal silver deposition in the form of a small distinct localized area (arrows) C= composite resin, A= adhesive; D= dentin Fig (5): SEM image of the interface bonded with Adper Prompt L-Pop showing greater and more intense silver deposition in the form of a small distinct localized area (arrows) when compared to G-Bond ( Fig 4) and Excite (Fig 6) C= composite resin, A= adhesive; D= dentin Fig (6) SEM image of the interface bonded with Excite. The silver deposition presented a less intense pattern when compared to Adper Prompt L-Pop (Fig 5). It was less continuing in the form of a dashed line(arrows) . The silver deposits were mostly located at the base of hybrid layer, but were sometimes also observed at the top. C= composite resin, A= adhesive; D= dentin Tables: Table (1): Materials used in the study:- Categories Materials Description Composition Manufacturer I- Adhesive systems 1. G-Bond (GB) Self-etch one step no mix adhesive Phosphoric acid ester monomer, UDMA, 4-MET, TEGDMA, Acetone, Water, initiators. GC America, St.Alxip. IL, USA. 2. Adper Prompt L-Pop (APL) Self-etch one step no mix adhesive Compartment 1: Methacrylated phosphoric acid esters, photo-initiator, Stabilizers Compartment 2: Water, HEMA, Polyalkenoic acid, Stabilizers 3M ESPE Dental Products, St. Paul, MN, USA. 3. Excite (Ex) Etch and rinse adhesive HEMA,DMA,Phosphoric acid acrylate, highly dispersed silicon dioxide,initiators and Stabilizers in alcohol solution. Ivoclar Vivadent Schaan, Liechtenstien. II- Restorative Materials 1. Tetric Ceram Light curing, fine particle hybrid resin composite BisGMA, UDMA, TEGDMA, Ytterbium trifluoride, Barium glass pigments and initiators. Ivoclar Vivadent III- Chemical reagents 1. Silver nitrate crystals Sigma Chemical Co.St. Louis. MO. USA 28% Ammonium hydroxide solution Table 2: Means and standard deviations of thickness of the interaction layer (ÂÂ µm) in tested adhesive systems Adhesive system Means SD 95% confidence intervals ANOVA P-Value Turkeys P-Value G-Bond (GB) 0.75 ÂÂ ± 0.16 0.49 1.00 Ë‚ 0.000 P1 Ë‚ 0.001 APL 1.65 ÂÂ ± 0.23 1.56 1.95 Ë‚ 0.000 P2 Ë‚ 0.05 Ex (control) 2.22 ÂÂ ± 0.23 1.53 2.50 Ë‚ 0.000 P1 Ë‚ 0.000 P1 : Turkeys comparison among the means of GB and APL. P2 : Turkeys comparison among the means of APL and Ex. P3 : Turkeys comparison among the means of GB and Ex. Table 3: Means and standard deviations of the sum of cavity margin lengths (ÂÂ µm) showing silver deposition in tested adhesive systems Adhesive system Means SD 95% confidence intervals ANOVA P-Value Turkeys P-Value G-Bond (GB) 12.70 ÂÂ ± 3.27 8.76 16.64 Ë‚ 0.001 P1 Ë‚ 0.002 APL 37.34 ÂÂ ± 6.56 28.83 45.85 Ë‚ 0.001 P2 Ë‚ 0.05 Ex (control) 20.74 ÂÂ ± 5.09 14.49 26.99 Ë‚ 0.001 P1 ˃ 0.05 P1 : Turkeys comparison among the means of GB and APL. P2 : Turkeys comparison among the means of APL and Ex. P3 : Turkeys comparison among the means of GB and Ex.

Human Evolution Essay

There is a theory that humans descended from an earlier, lower form of life. There is an assortment of evidence that shows that all living creatures on Earth descended from a common ancestry. Evolution doesnt discriminate against humans. It is believed that we too are a product of an earlier predecessor. The similarities in all life are evident if you consider that every form of life builds from the same building blocks–20 essential amino acids, four nitrogen bases, and simple sugars. Each of Earths past and present forms of life are, or were composed of a combination of those building blocks called RNA or DNA. In the very beginning of life on Earth, the genetic structure was very simple, but as time has gone by, the best combinations in the genetic sequence were individuals that reproduced. Over the approximated 3.5 billion years that life has been in existence on Earth, there have been many mutations in the genetic codes of different forms of life. Only very few of the genetic mutations are indeed beneficial to the function of the species. Negative mutations give the life form a disadvantage for survival, thus reducing its chances for reproduction, but a positive mutation gives the species an advantage to survive and produce offspring. The offspring have a copy of the positive mutation now in their genetics to eventually pass down to their young and so on. Now you can see how the positive mutations have a way of piling up into different piles, which is why our result is a widely diverse life, which exists on Earth today. This theory of how evolution came to be is known as natural selection. It states that a weaker individual has a lesser chance for survival and reproduction than that of a stronger. Its natures way of weeding out the bad and seeding the good. In the study of evolution, evolutionary scientists try to find the ancestry and genetic relations between organisms. They try to map out the path of the ancestry between organisms over the existence of the Earths history. Another essential part of the study of evolution is actually making educated predictions of the history of a species. The history of a species includes the geographical distributions and the species population over time. All of the information that follows is valid in that it has genetic and fossilized evidence to prove its merit. Some of the most important aspects  that make a human different from its ancestors are the development of communication, brain function, and the ability to walk upright, which frees up the hands to embark on other tasks. Language is considered by many to be the most unique of all the human attributes. As strange as it may sound, genetically we are the most similar to that of primates as any other known living creature on Earth. The primate family includes chimpanzees, orangutans, gorillas and even humans. Other than genetic similarities, we can show other likenesses in the tissue physiology and also by comparing brains circuits in a brain analysis. Humans are a prime example of natural selection. The domination of the world by the superior present day human is what ended all similar species. The species that we dominated were our greatest competition for food, intelligence, and essentially our very existence on this planet. When we beat our predecessor, we did it in a fight for our lives, not so much as an act of violence. In many cases, Humans may have killed our ancestors in a misunderstanding, not knowing why a similar being was so much more savage and violent. We may have protected our families by attacking these beastlike creatures. The first things that we need to know are, Who were our first ancestors? Why did they evolve? What did they look like? And how did they live? Without this information, we will not know what we have arisen from. The most likely place to look for our fossilized lineage is in the environment of our closest living relatives–Africa. This is the reason that most of our archeological digs have been occurring on this continent. Of the fossils found, the skulls have been the most important because by knowing the structure of the skull, we can see how distant their relations are to us. Since one of the most significant changes is brain size and function, the brain and brain cavities provide a lot of evidence for evolutionary change. We know about brain function from fossils because sometimes, even the brain is preserved inside the fossilized skulls. Our most distant known lineage into the human path is very much similar to that of a chimpanzee. This creature was known as Australopithecus afarensis and can be dated back to 3.2 million years ago. A. afarensis was still very similar to a chimp. The brain size was no larger than ours. The finger bones were still curved, showing that it was still quite comfortable in the trees. Even though it was slightly similar, it was still very different. A. afarensis had smaller canines than a chimpanzees. The face structure was more vertical with less snout. The spinal column was more upright than that of a chimp. The hip bones also showed something unusual–this animal walked upright. This was the first step in our direction from that of our most distant living relative. The famous Lucy fossil was the remains of an A. afarensis. This fossil showed that the A. afarensis, although different than chimps, still had a small rib cage and a large gut that was fit for digesting the large amount of vegetation that made up their diet. From the large gut, we can speculate that the diet of A. afarensis consisted of still mainly vegetation, and not yet much protein. While the Australopithecus afarensis existed, there was a great climate change in Africa. The once tropical African continent warmed and the main portion of the continent closest to the equator turned to dry grassland. The food that A. afarensis was accustomed to eating, had disappeared. Many of the chimps, like other animals, migrated south to the bottom tip of Africa. There in the forest, this upright primate had a disadvantage to the chimps, so it quickly died off in the forests. The Australopithecus that stayed had to adapt to survive. There was very limited food that these creatures could digest; they could not process the fibrous grasses that covered the plains. The Australopithecus split into two different forms of the species–a robust more animal-like version and a graceful more human-like model. The robust version adapted to eat the roots of plants. The tough root and difficult dig to obtain the meal resulted in a large-jawed, thick-skulled, digging creature. The smaller, more graceful was the one humans are in closest relation to. We find it evident in the size and shape of the brain found in fossils. These are the first of our ancestors that used stone tools. These  stone tools were the adaptation that fueled their kind. The stone tools at the time and great intelligence were what allowed them to obtain food. When scavenging for food, they would take a completely cleaned animal carcass and using their simple stone sledges, smash open bones and eat the protein rich marrow from within. They would also use their hammers to crack open the skull to obtain the brain, which was also rich in protein. The advantage here is that they had no competition for their newly found food because no other creature could access these meat reserves. The protein they were ingesting was food that was high in energy and much easier to digest than plant material. After generations went by, the large digestive track was slowly shortened because it was no longer needed. As the size of the animal lessened, the ratio between weight and energy rose. This gave room for the brain of these graced Australopithecus to adapt to the environment, and since intelligence is what kept this branch alive, their intellect developed more. The individuals who where the most intelligent made the best tools, and thus had a better chance for survival and reproduction. Tools, meat, and larger brains were the reasons that this species strived, but if you take out any of these vital parts, the others couldnt develop. Homo erectus is the next known ancestor down the branch to humanity. He dates back to 1.8 million years. H. erectus looked much like human, but still had a mind no more complex than a chimps. The brain of H. erectus was still 30% smaller than our own. Homo heidelbergensis shows much more human-like characteristics than its predecessor, Homo erectus. The first evidence of H. heidelbergensis in Europe dates back to .5 million years ago. There have been 5 tons of remains found in circle patterns in a small area. The circle patterns are evidence that they were living in round, maybe hut-like enclosures. When you consider the small area in which they were found, you can see that possibly they lived in a small community. Now living in Europe, having shelter was essential because Europe was a great deal cooler than their arid grasslands in Africa. Shelter is probably what allowed them to venture out of Africa for the first time, because without that support, they would surely freeze in the cold season. In a cave in Italy, scientists have found the skeletal  remains of one of these male creatures and the skeleton was preserved quite well. Deep in this cave, it has been partially covered by crystals that the cave has formed. By measuring the size of these bones, we know the size of this creatures male gender. This Creature used stone tools, but they used better stone like flint. Their tools were much sharper and lighter. They have found that they chipped hand axes out of flint that are much more complex than that of the previous. They also showed that they had many of the flint remains in one area, signifying that they used mass production to obtain their tools. They used theses sharp tools to butcher animals, meaning they had made the kill and no longer were only scavenging meat. At this time in history, animals, such as rhinoceros, elephants, lions and the largely extinct cave bear existed in Europe. H. heidelbergensis had a brain size very close to the size of a present day human. They used different tools when disassembling these large animals. They used large rocks for smashing bones, which enabled them to retrieve marrow from their thick bones. They harvested some of the bones from these creatures for tools in various activities. Their sharp flint tools were used to remove the meat from the bone. They also used antlers to dig and punch an initial hole in the carcass before butchering it. There is evidence that .5 million years ago when we know they had inhabited Europe, they not only were living there, but were also flourishing. This shows that they may have been there for many years prior. It isnt fully understood about why they migrated out of Africa and into Europe. In the new cooler climate, their edible vegetation was scarce; therefore there were less food options. The only two options were to scavenge or adapt. Our ancestors, like before, rose to the occasion and adapted to become hunters. They became hunters to eliminate scavenging against the ravage carnivores of their day. In Europe H. heidelbergensis was more advanced than the H. heidelbergensis of other areas. The advancements in the H. heidelbergensis of this area are evident in their tools. It is believed that the Europeans used language. This is proven by their methods of passing down knowledge. This much larger axe head was too large  for actual function. It was probably used as a model to show the detail of the axe head. Their scale model was proof that they must be teaching the art of tool making and in the process, using complex communication. This language was likely to be very simple to the language we know today, but it allowed them reflect on the past and to teach more efficiently. Even though their tools couldnt take down some of the larger prey, their intelligence proved itself again. They used swamps as traps, and would drive a large animal into a corner, where it would then have to retreat into the swamps. Once they entered, they couldnt escape the quicksand-like substrate. There is also evidence of the use wooden tools. Archeologists have found perfectly preserved wooden spears in the prehistoric swamps. When they examined the spears, they found that the tip was on the toughest part of the wood–the base. These spears were also found to be perfectly balanced, so they could be used as javelins. This was another step into humanity. They now had more food for themselves, their mate and their offspring. Neanderthals had a very robust build; they were short and very strong unlike anyone today. It is known from fossil records that Neanderthals disappeared at almost the exact time that that humans arrived. It has been widely believed for years that Neanderthals were our predecessors, but today we can tell that Neanderthals were a completely different, but almost parallel evolutionary relative. This is known by genetics. The last known Neanderthal fossil dates back to 28 thousand years ago. Before the humans invaded the land, the territory belonged to the Neanderthals. Their brains had completely different evolutionary paths than us; they may have appeared very similar to us, but were, in actuality, quite different. The brain of the Neanderthal evolved differently and not as drastically as that of the human brain. The evolution of the Neanderthals mind hit a plateau, and it is seen in the fossil records that the tools of the Neanderthals remained unchanged for a quarter million years before their extinction. Other than human competition, the main reason for the disappearance of the Neanderthals was a change in climate and landscape. They couldnt survive in an area with a disappearing habitat. They were so dependent on what they were accustomed to, that the transition couldnt be made and the result was an eventual  extinction of their species. In the rapidly cooling European areas, humans used their intelligence to adapt, but Neanderthals were isolated to pockets of still wooded areas. One by one, the Neanderthals died off. Homo sapiens date back to over 100,000 years ago, as the skull fossils found in Africa show. These humans were still quite primitive, but the bone structure was that of a present day human. Now that Neanderthals had disappeared, this meant less competition for our human ancestors. This is a perfect example of Charles Darwins theory of survival of the fittest. They couldnt adapt and died, and could no longer pass on their genes. We survived and we continue to procreate. Using decorative beads is one of the first examples of art in our species. One of the beads found was made of shell. The strange thing about this shell bead was that it was found hundreds of miles away from where it first lied. This is evidence that humans may have been trading with neighboring tribes. Another possibility is that they traveled the distance to retrieve the shell, but this proves that they were traveling into a much cooler climate. If they were able to survive in this cooler area, then they must have also been wearing warm clothing and building sturdy shelters. We have found decorative beads with the remains of Neanderthal bones. Not many of the recorded Neanderthals, in fact, used beads. Some consider that to show they used art also, but others believe it was simply them mimicking what they had seen their human counter parts doing. The Neanderthals beads were much more primitive, but that may be partially due to them being unable to grasp the function of the decoration as a form of self expression. This is a prime example of the similarities and differences in the minds of the two creatures. There is a theory that the last few Neanderthals had to interact with humans. In this theory, there is a possibility that some Neanderthals breed in hybridization between the two. If this were the case, then most of us would have traces of Neanderthal genes hidden in our genetic sequences. Humans used beads as barter and it aided in the process of large alliances and community. In their trades, they thought it was necessary for them to be civilized, which would also help shape, what we have become today. After they had migrated out of Africa, it was first believed that humans quickly inhabited Europe. Now, contrary to that belief, there is evidence that we slowly moved into Europe and had inhabited the new continent for quite some time. Humans were the most dominate of the two, taking over the food and habitat of the last living Neanderthals. Humans are the present day victors. We have shown our capabilities and superiority and only time will tell where we evolve from here. Anthony M AikinWork CitedDoolittle, Russell. â€Å"Evolution.† McGraw-Hill (2000): 4. Futuyma, Douglas. â€Å"Organic evolution.† McGraw-Hill (2004): 11. Rightmire, G. Philip. â€Å"Human evolution in Eurasia.† McGraw-Hill (2004): 4. Wilson, Edward. From So Simple A Beginning. New York City: W. W. Norton & Company Inc., 2006. Dawn of man Vol. 1. Dir. John Lynch. Videocassette. British Broadcasting Corporation, 2000. Dawn of man Vol. 2. Dir. John Lynch. Videocassette. British Broadcasting Corporation, 2000. Dawn of man Vol. 3. Dir. John Lynch. Videocassette. British Broadcasting Corporation, 2000.

Affirmative Action Debate and Economics

Yuching Lin ECON 395 The Affirmative Action Debate Affirmative Action has recently become the center of a major public debate in the United States, which has led to the emergence of numerous studies on its efficiency, costs, and benefits. The Civil Rights Act of 1964 and Equal Employment Opportunity Commission ended wage and employment discrimination based on gender and race, significantly decreasing the gap between minorities and non-minorities. Minorities made major progress from the 1960s up through the early 1970s due to Affirmative Action (Jones, Jr. 1985). However, for the past few decades, the progress that minorities have made in terms of income, employment and education has largely stagnated. California, Michigan, Nebraska, and Washington State have recently banned racial advantage in employment and college admissions, and Proposition 209 of California has disallowed the preferential treatment of minorities, with opponents of Affirmative Action lobbying for more widespread b ans on similar policies while supporters argue fiercely against the removal of Affirmative Action policies.As can be seen, Affirmative Action’s status in the United States now is very dynamic due to shifting court decisions and policy plans. Additionally, returns to education have been increasing in recent decades, and as a result, income inequality has also increased – the growing demand for highly skilled workers (workers with high levels of post-secondary education) and the stagnancy of American education (with the added fact that high quality colleges have become even higher quality and even more selective while lower tier colleges have decreased in quality) has led to ever-increasing wages for the highly skilled.This â€Å"Skill Biased Technological Change† has led to a widening income gap between the rich and the poor. Naturally, this considerably affects black and Hispanic minorities, who are more likely than non-minorities to be part of the working class or below the poverty line, which raises the stakes in the debate on Affirmative Action. Today, both sides on the debate can bolster their arguments with evidence provided by economic and social research on the policies. But there are additional questions to be answered – is Affirmative Action justified on moral grounds? Can we balance economic efficiency with equity?Is Affirmative Action the best policy for addressing racial inequalities? Do policies that increase diversity result in positive externalities such as reduced prejudice and indirect benefits beyond education and career success? One will discover that, after thorough analysis of research concerning Affirmative Action, it is still difficult to form a definitive conclusion on the results of the policies. Nevertheless, there is much to learn from the research that has been conducted as of present, and one can now better steer research in a direction that will uncover the real benefits and shortcomings of Affirmative Action.To begin with, the debate on the efficiency of Affirmative Action policies is still very much unsettled. Opponents claim that they actually result in several negative effects on the minorities the policies are intended to benefit, arguing that minority students admitted into overly competitive programs are more likely to drop out than mismatched non-minority students due to the increased competition, which would actually worsen the income gap since black income has been shown to decrease even more than white income after dropping out of college (Loury, 1995).A proposed â€Å"stigma hypothesis† suggests that â€Å"preferential treatment perpetuates the impression of inferiority† while simultaneously lowering incentives for high academic effort from minorities (Murray, 1994). And yet another underperformance hypothesis by Steele (1990) suggests that blacks’ academic performance suffers when they are aware that normal standards are lowered in order to accomm odate them.However, there exists no research with strong, conclusive results that support these claims – in contrast, the â€Å"race difference in graduation rates is no larger at the most selective institutions,† and blacks have been shown to benefit from the increased admission to selective universities (Holzer and Neumark, 2000). A study by Cortes (2010) on the Texas Top 10% Plan claims that the banning of Affirmative Action actually increases college dropout rates for minorities and finds that the mismatch hypothesis is inaccurate.Because quantifying the economic benefits of Affirmative Action is exceedingly complicated, comparing the total costs and benefits of the policy becomes exceptionally difficult for policy-makers. Holzer and Neumark (2000) note that university admissions policies are not necessarily economically efficient to begin with, which further complicates matters since researchers do not have a definitive point of efficiency to which they can compar e the results of Affirmative Action.Administrative costs and externalities must also be factored into the models, when economists have not yet even managed to create a viable model for the effects of Affirmative Action policies. For example, minority students in medical school are less likely to reach as high a level of expertise as non-minorities, but they are more likely to treat minority patients, generating a positive externality (Holzer and Neumark, 2000). Another point made in the debate on Affirmative Action is that diversity may improve the educational quality of a university.Many educators believe that diversity in colleges is inherently beneficial – students can learn from other students whose experiences and backgrounds give them a whole different set of views and capabilities. Several studies have actually correlated increased diversity in student bodies with improvements in issues such as racial prejudice and bias, although results vary depending on study design, extent and type of diversity, and the issue of interest (Bowman, 2010).Even so, other researchers are likely to reject such evidence since variables such as attitudes, inter-racial relations, and even school quality (as a result of increased diversity) are difficult to define and accurately quantify (Holzer and Neumark, 2000). Research has often demonstrated very unclear results, usually only weakly suggesting a few conclusions while also providing sometimes conflicting conclusions; one study on the effects of diverse student bodies found that there was no effect on post-college earnings, an increase in satisfaction with college experiences, and a decrease in community service (Hinrichs, 2011).Interestingly, a recent study in college admissions based on merit, race, and legacy suggests that the removal of race-preferential treatment may actually decrease the ability of the student body since colleges may be inclined to increase legacy-based admissions due to the current economic cl imate (Li and Weisman, 2011). However, they do also propose that there is a possibility that colleges would need to eliminate all preferences barring merit in order to produce the most-able student body.Overall, it is generally agreed that more accurate methods for measuring school quality and the quality of school inputs are necessary if more conclusive results on education differentials’ effects on unobserved skills, attitudes, and racial income inequality are to be found. While it is without a doubt that Affirmative Action increases admission and employment rates for minorities, there is much speculation as to whether it is the most effective policy. Researchers are not confident yet of how different variables interact to affect income, employment rates, and other indicators of success.As a result, one will often find seemingly conflicting data as exemplified by Card and Krueger’s (1992) findings that â€Å"5-20% of the post 1960 black gains were due to improved sc hool quality† while Smith and Welch (1989) claimed that 20-25% of black gains were a result of improved school quantity, which they asserted should be the focus of educational policies. Moreover, it is well known that employers often discriminate based on race, whether purposefully or unconsciously, and that this significantly impacts labor market outcomes.Affirmative Action can only do so much to address employment discrimination – in some models, the issue of negative racial stereotypes can be exacerbated by the application of such policies (Holzer and Neumark, 2000). In addition, some suggest targeting education inequalities in primary and secondary education as opposed to implementing race-preferential treatment in post-secondary education as a more efficient and equitable policy, although efforts such as NCLB have only slightly improved primary and secondary education inequalities.The primary and secondary education quality in the United States is in dire need of i mprovement already; high school graduation rates have stagnated, and school quality is falling behind when compared to the educational systems of other developed countries. There also exist other complicated variables that need to be addressed in order to close the income gaps between minorities and non-minorities such as the inheritance of learning abilities/behavior, ghetto culture, and the underclass (Jencks, 1993). As one can expect, research concerning controversial issues often suffers from researcher bias.Economic research typically entails numerous variables and methods in order to reach conclusions, and more often than not, results are varied and ambiguous, especially in this particular branch concerning Affirmative Action. It is a simple matter to selectively exclude certain results in order to make it appear as if a research study conclusively supports or rejects Affirmative Action as a beneficial policy, should one wish to do so. Literature searches can quickly turn up v ery obviously biased articles with weak evidence and unreasonable claims.Furthermore, past research has indicated that the types of models used in studies can have a significant impact on the results, further obfuscating the conclusions on the effectiveness of the policies. In fact, as of present, research on the policies has resulted in mostly ambiguous conclusions, although it is of my opinion that studies in general very slightly lean toward suggesting that Affirmative Action is beneficial as a whole – research studies that conclusively reject Affirmative Action as a viable policy are few and far between, and it is even difficult to find studies that demonstrate significant negative effects.In order to obtain more accurate data, researchers would optimally be able to create experimental studies with control and treatment groups, but this is very unlikely to occur due to the unethical properties of such studies. Clearly, it has become even more imperative that researchers i mprove models on the efficiency of Affirmative Action policies in order to obtain more reliable data to demonstrate with greater confidence the effects of the policy. Of course, these topics only cover the economic justifications for Affirmative Action, which is clearly also a matter of social justice.There is an endless cycle of philosophy-based debates on the policy – should we as a society aim for equity or efficiency? If we are willing to sacrifice some efficiency for equity, how much is optimal? There is also the question of whether society has a responsibility to â€Å"[remedy] the present effects of past discrimination,† which begins another entire debate about the responsibility of people today for wrongs committed by ancestors (Jones Jr. , 1985).Some also believe that Affirmative Action devalues the achievements of minorities since credit may be given to race-preferential treatment instead of to the individuals who accomplish those feats; this can lead to furt her racial prejudice and bias, possibly encouraging the continuation of racial discrimination in job employment. There are also suggestions that perhaps policies ought to focus on helping the part of the minority population with low socioeconomic status so as to avoid situations in which wealthy black students may be given preferential treatment over more qualified white students living below the poverty line.The debate over Affirmative Action for women is also just as controversial, for women also suffer from income inequality, but they still receive the same advantages that their male siblings receive. Therefore, one can argue that women are not put at a disadvantage early on in life and that they should not require preferential treatment in admissions or employment. In fact, women who benefit from Affirmative Action are much less likely than racial minorities to be lower-qualified and less-skilled, suggesting that implementing a preferential treatment policy may be inequitable in this case.Even more abstract of an argument is the claim that men and women will never reach perfect equality since they inherently desire different careers and hold differing aspirations for lifetime achievements. As can be seen, there is literally a myriad of issues that factor into the debate on Affirmative Action. The field of research concerning the topic is beset by the typical problems plaguing education and economics research – education quality and educational inputs to schools are difficult to measure, as are the effects on income, employment rates, job characteristics, etc. The lack of experimental data lends no help.The effects of nationally implemented legislation are difficult to track and quantify because of differences over time and across states (Altonji and Blank, 1999). Compiling data at a national level is also vastly time-consuming and challenging. Though neither side has conclusive evidence that supports their argument, studies that reveal tentative con clusions on the effects of Affirmative Action policies are emerging, and models are slowly approaching real-world utility. As research continues, hopefully the accumulation of data and models will allow researchers to uncover the true effects of Affirmative Action.References Altonji, Joseph G. and Rebecca M. Blank. 1999. â€Å"Race and Gender in the Labor Market. † In Handbook of Labor Economics, edited by Orley Ashenfelter and David E. Card, 3143- 3259. San Diego: Elsevier B. V. Bowman, Nicholas A. 2010. â€Å"College Diversity Experiences and Cognitive Development: A Meta Analysis. † Review of Educational Research 80(1):4-33. Card, David and Alan B. Krueger. 1992. â€Å"School quality and black-white relative earnings: a direct assessment. † Quarterly Journal of Economics 107:151-200. Cortes, Kalena E. 2010. â€Å"Do Bans on Affirmative Action Hurt Minority Students?Evidence from the Texas Top 10% Plan. † Economics of Education Review 29(6):1110-1124. D ong, Li and Dennis L. Weisman. â€Å"Why Preferences in College Admissions May Yield a More- Able Student Body. † Economics of Education Review 30(4):724-728. Hinrichs, Peter. 2011. â€Å"The Effects of Attending a Diverse College. † Economics of Education Review 30(2):332-241. Holzer, Harry and David Neumark. 2000. â€Å"Assessing Affirmative Action,† Journal of Economic Literature 38:483-568. Jencks, C. 1993. Rethinking Social Policy: Race, Poverty, and the Underclass. New York: HarperPerennial. Jones Jr. , James E. 1985. The Genesis and Present Status of Affirmative Action in Employment: Economic, Legal, and Political Realities. † Iowa Law Review 70:901-923. Loury, Linda D. and David Garman. 1995. â€Å"College Selectivity and Earnings. † Journal of Labor Economics 13:289-208. Murray, Charles. 1994. â€Å"Affirmative Racism,† In Debating Affirmative Action: Race, Gender, Ethnicity, and the Politics of Inclusion, edited by Nicolaus Mills. 1 91-208. New York: Delta. Steele, Shelby. 1990. The Content of Our Character. New York: St. Martin’s Press. Smith, James P. and Finish Welch. 1989. â€Å"Black Economic Progress after Myrdal. † Journal of Economic Literature 27:519-564.

Examine the Themes of Innocence and Experience in To Kill...

Examine the Themes of Innocence and Experience in To Kill a Mockingbird Innocence is a time when a person has never done something; it is the first step of the journey from innocence to experience. The second step in this movement is experience and this is what is achieved after a person has done something they have never done before or learns something they have never known before. This theme of growth from innocence to experience occurs many times in To Kill a Mockingbird and is one of the central themes in the first part of the novel, because it shows how Jem and Scout change and mature over a small period of time. Jem, Scout and Dill find ways to use their boundaries, in conjunction with their imaginations to amuse†¦show more content†¦When Walter returns with the Finches for lunch, Scout comments on Walter’s table manners and I once again scolded but this time by Calpurnia. This is another example of innocence as Scout finds the way Walter eats unusual and was only curious. Prior to these events happening, Scout had never known that it was improper to make fun of or judge a guest of the house. In her innocence, she had never before realized this behavior was inappropriate. However, become experiences as Scout learns never to repeat these actions. In Chaper 5, Scout starts to feel excluded by Jem and Dill. This may be because she is younger or because she is female, but she substitutes their company with Miss Maudie’s. On one occasion, it seems she does not fully understand the implications of her conversations with Miss Maudie. She thinks that Miss Maudie has accused Atticus of drinking. Scout also misunderstands Miss Maudie’s conversation with Miss Stephanie. As well as showing Scout’s innocence, these two instances become opportunities for humour. Another example of innocence and experience in the novel is in chapter 6, on the last night of the summer holidays, the children approach the Radley house to look through the window, during one of their games. As Jem advances to the steps a shadow crosses him and the children run away. Jem catches his trousers on the fence andShow MoreRelatedHow Does Harper Lee Portray the Themes of Innocence, Maturity and Growing Up in to Kill a Mockingbird ?1053 Words   |  5 PagesIn ‘To Kill a Mockingbird’ written by Harper Lee, the author has used numerous different methods to portray the themes of innocence, maturity and growing up. These themes were put in so that the audience could become more empathetic towards the characters, especially the protagonists. She depicts these themes through characters, events, using symbolism, imagery and contrast located throughout the book. Firstly, Harper Lee shows the themes of innocence, maturity and growing up through the mainRead MoreWhat Makes Lees To Kill A Mockingbird a Literary Classic1008 Words   |  4 PagesTo Kill A Mockingbird is a prime example classic modern literature, having won the Pulitzer Prize. Elements that have helped deem worthy of such classification, consists of its exploration of universal themes, the memorable and relatable characters who help define the story, and its addressing of issues that even now are common in today’s society, being able to evoke thoughts and emotional responses from its audience, helping them to define the world around them. It truly is a masterpiece. To beginRead MoreTo Kill A Mockingbird Essay1505 Words   |  7 PagesRaising children in the era of Jim Crow laws provided a unique teaching experience for Atticus to provide to Scout and Jem. These laws followed the Southern societal ideas of the separation between races, but also demonstrated a division between a community where individuals held different moral ideas. To Kill a Mockingbird explores human morality from the perception of a six year old child, providing a different perspective on important issues of this time period. Scout’s understanding of moralityRead More Mythology and Archetypes in Harper Lees To Kill a Mockingbird2536 Words   |  11 PagesMythology and Archetypes in Harper Lees To Kill a Mockingbird      Ã‚  Ã‚   Of all the various approaches to criticism, the Mythological/Archetypal achieves the greatest impact over the entire literary scope, because the themes and patterns unearthed apply universally to all works, yielding results that can be applied to a great many texts. This is because the very nature of the Mythological/Archetypal approach is the exploration of the canon for widespread and pervading symbols, plots, andRead MoreComparing Themes of To Kill a Mockingbird and A Raisin in the Sun1962 Words   |  8 PagesTo Kill a Mockingbird and A Raisin in the Sun are books both written during a time of racial tension and inequality. Harper Lee and Lorraine Hansberry lived through the civil rights movement and saw the physical and verbal harassment against African Americans. This experience is evident in both works as the theme of fighting prejudice shines through. The goal of this paper is to compare and contrast the theme in both books and how it affected both of the families. Also, throughout the paper I willRead MoreReading Notes On Kill A Mockingbird3311 Words   |  14 PagesMarcus Djuhadi Mrs. Dunn P.D. American Literature, Period 6 To Kill A Mockingbird - Reading Notes Summary // Style Language // Response // Other PART ONE Chapters 1-3 Main character introduced: Jean Louise Finch (â€Å"Scout†) Her older brother: Jeremy Finch (â€Å"Jem†) Father: Atticus Finch, works as a lawyer Mother died when Scout was 2, Jem remember her but Scout does not Jean Louise explains her ancestral roots; her family seems financially secure Maycomb, Alabama is the exposition - fictional, butRead MoreA Mockingbird, By Harper Lee5251 Words   |  22 PagesZwierschke 1 Alicia Zwierschke Mrs. Reade ENG2D4 19 May 2015 Man’s Inhumanity to Man in â€Å"To Kill a Mockingbird† A mockingbird is a harmless bird that makes the world a more pleasant place. In â€Å"To Kill a Mockingbird†, by Harper Lee, the mockingbird symbolizes Boo Radley and Tom Robinson/ They were both more than peaceful people who never did harm, until a man’s inhumanity hurt them or ruined their life. This novel exposes the inhumanity through various scenario’s throughout the telling of Scout’sRead MoreHow To Write Literary Analysis4174 Words   |  17 Pagesin the world. When you read a work of literature in an English class, however, you’re being asked to read in a special way: You’re being asked to perform literary analysis. To analyze something means to break it down into smaller parts and then examine how those parts work, both individually and together. Literary analysis involves examining all the parts of a novel, play, short story, or poem—elements such as character, setting, tone, and imagery—and thinking about how the author uses thoseRead MoreLiterary Criticism : The Free Encyclopedia 7351 Words   |  30 Pagescinematic form, the coming-of-age film. Plot outline[edit] A Bildungsroman relates the growing up or coming of age of a sensitive person who goes in search of answers to life s questions with the expectation that these will result from gaining experience of the world. The genre evolved from folklore tales of a dunce or youngest son going out in the world to seek his fortune. Usually in the beginning of the story there is an emotional loss which makes the protagonist leave on his journey. In a BildungsromanRead MoreNoughts and Crosses14387 Words   |  58 Pagessuch book to repeat the experience, again and again. Fortunately, contemporary writers of fiction for young adults continue to offer us fresh opportunities to enjoy literature with our students. Oxford Rollercoasters is a series that offers teachers the opportunity of studying first-class novels – recently written for teenagers – as whole-class readers with Year 7, 8 and 9 students. Focus on assessment of reading Oxford Rollercoasters includes titles with varied themes, challenging subject matter