Figure 1. A Cat's Pupil. Depending on the relative light present, the shape of a domestic cat's pupil changes from a vertical slit, to an almond shape, to almost fully round. Photo by wapiko available at: https://farm8.staticflickr.com/7170/6485554303_293163fb27_o_d.jpg under CC BY 2.0 license.
The panselectionist viewpoint is the theory that natural selection acting on genetic variation is virtually the only acceptable mechanism of evolutionary change. Darwin did not support panselectionism. Though he considered natural selection to be the most important mechanism of evolution, he held a pluralistic viewpoint in which he insisted his theory did not rely on natural selection alone. In contrast, Wallace did ascribe to panselectionism, believing that all variation must be in some way adaptive. The authors of the article The Spandrels of San Marco and the Panglossian Paradigm hold Darwin’s view that, though natural selection is perhaps the most important instrument of evolution, it is certainly not the only one. One alternative mechanism the authors mention is selection without adaptation. They offer a hypothetical example in which a mutation that significantly increases the fertility of individuals occurs. It would proliferate quickly within a population, but unless it also caused a change in efficiency of resource utilization, the individuals will just lay twice as many eggs, with the excess dying because of limited resources. If a predator that eats eggs is led to switch to the species now that the eggs are more plentiful, the population size may actually decrease as a consequence, yet natural selection at all times will favor individuals with higher fecundity, despite the organism not being any better adapted. Another example is genetic drift. Due to limitation on population size, the groups that form the first step in the speciation process are often founded by only a small number of individuals. As a result, frequencies of alleles change by random genetic drift, and populations will become genetically differentiated despite the absence of any selective force.
The article “A Complete Skull from Dmanisi, Georgia, and the Evolution of Early Homo” describes archaeological finds from a site in central Asia and their relevance to early hominin evolution and migration. Excavation began on the Dmanisi site in 1999, with researchers first finding assorted fauna fossils, then stone tools, and finally hominid remains. These hominid fossils have been linked to H. habilis and H. erectus in Africa and H. erectus in East Asia. The hominid remains in Dmanisi are especially important because they have been dated to 1.8 million years ago, and thus represent the earliest hominid finds outside of Africa, casting doubt on previous assumptions as to when human ancestors first travelled to other continents. One of the main focuses of the article is a particular fossil known as skull 5, which is the first and only completely preserved adult hominid skull found from the early Pleistocene. This fossil is important because it provides evidence of the orientation of the face relative to the brain case, and serves as an intact sample of fully developed adult cranial morphology, which was previously unavailable due to earlier finds being either incomplete, damaged, or juvenile skulls. Skull 5 is described as having small brain case, a large, prognathic face, and very robust features. Skull 5 in the context of the 4 other sets of remains, also shows distinct morphologic variations, despite almost certainly being of the same species, since they were all found in the same general location and dated to approximately the same time. The notable anatomical differences in the shape of the skulls led researchers to measure the morphological variation between the Dmanisi finds and compare it to the variation found in extant ape species, like chimpanzees and bonobos. This analysis led them to conclude that the variation in the Dmanisi fossils is well within the range of normal variation within a species population. The article went on to say that such a conclusion raises questions about whether previous finds from elsewhere in Asia and Africa, which were categorized as separate and distinct species, are in fact merely part of a single widespread Homo lineage.
Fierce Green Fire: The Battle for a Living Planet is a documentary made by Mark Kitchell and inspired by the book of the same name by Philip Shabecoff. Shabecoff named the book after the phrase used by a forest ranger to describe the look in the eyes of a wolf he had killed, which awakened the ranger’s understanding of his role in the “web of life” and the consequences of chipping away at that web. The film chronicles the environmental movement of the last half century, told through five acts, each with a central story and character. These acts include David Brower and the Sierra Club’s battle to halt dams in the Grand Canyon, Lois Gibbs and Love Canal residents’ struggle against 20,000 tons of toxic chemicals, Paul Watson and Greenpeace’s campaigns to save whales and baby harp seals, Chico Mendes and Brazilian rubber tappers’ fight to save the Amazon rainforest, and Bill McKibben and his 25-year effort to address climate change. Woven throughout these main stories are shared themes like environmental justice, valuing the land simply for the land’s sake, and humanity’s place as simply one strand in the web of life. Vivid archival footage offers viewers first hand insights into the stories and informative interviews shed light on the events in larger context. The film offers a deeper view of environmentalism as civilizational change, bringing our industrial society into sustainable balance with nature.
A wetland is a distinct ecosystem that is inundated by water, either permanently or seasonally. The primary factor that distinguishes wetlands from other landforms or water bodies is the characteristic vegetation of aquatic plants, adapted to the unique hydric soil. A hydric soil is defined by federal law to mean "soil that, in its undrained condition, is saturated, flooded, or ponded long enough during a growing season to develop an anaerobic condition that supports the growth and regeneration of hydrophytic vegetation.” Wetlands are considered the most biologically diverse of all ecosystems, and are home to many species of migratory and resident birds, reptiles and amphibians, fish, insects, and plants. In addition, they benefit us by storing floodwaters, filtering pollutants, and serving as a carbon sink. The southeastern region of the United States specifically was once home to expansive wetlands, but the Mississippi River Delta and coastal Louisiana have been disappearing at an astonishing rate. Since the 1930s, Louisiana alone has lost over 2,000 square miles of land, an area roughly the size of Delaware. Many factors have contributed to this collapse, including the construction of levees, dams, oil and gas infrastructure, shipping channels and canals, as well as the addition of invasive species. Furthermore, many researchers cite climate change and the resulting rise in sea levels and worsening storms as major contributors.
The Socioecological Model is a method of categorizing female social relationships through agonism. This is further examined along three social dimensions. The first dimension seeks to establish whether or not a dominance hierarchy is present in the given group being analyzed. A group which lacks a strict hierarchy is defined as egalitarian, in which there are undetectable or poorly defined dominance relationships, or in which the dominance hierarchy is not clear or nonlinear. In these groups, food is often dispersed in a way such that patches cannot be defended, resulting in scramble competition in which the first female to arrive at a food resource may get a larger share of the food simply because she got there first. This means there is nothing to gain from contesting the resource, and thus typically produces weak social relationships in females, with no need for post conflict resolution like grooming. In contrast, a group which exhibits a strict hierarchy is known as despotic, in which there are clearly established, formalized dominance relationships that are usually linear. When there is competition over essential resources, aggressive interactions maintain dominance hierarchy and contest competition is high. High rank can provide priority of access to resources, and potentially higher reproductive success, and may may also result in alliances or affiliative behaviors like grooming. The second dimension aims, once a hierarchy has been observed, to further classify the type of hierarchy present. There may be a nepotistic hierarchy, in which female relatives rank close together due to coalitions and often don’t disperse, or individualistic hierarchies, in which the rank of female relatives are independent of each other, and females do disperse. The third and final dimension seeks to assign the degree of tolerance within the group structure, and generally assumes that as tolerance increases, the severity of aggression decreases while threats toward dominant individuals increases.
Historically, there have been two competing taxonomic systems used to classify the suborders of primates. Tarsiers were initially categorized alongside lemurs and lorises, and apart from humans, apes, and monkeys. This original taxonomic system, known as the gradistic division, held that the two suborders of primates were Prosimii and Anthropoidea. Prosimians, which means “before apes”, were comprised of lemurs, lorises, and tarsiers, due to the perception that they represented grades of evolution. They were seen to possess many of the same traits, such as similar teeth, skull, and limb anatomy to early, now extinct, primates. These “primitive” features being shared amongst the three extant groups were believed to be evidence of close relation, and were thought to set them apart from the “more evolved” characteristics of anthropoids. The more recent categorization, known as the phyletic division, posits that tarsiers should actually be grouped alongside monkeys, apes, and humans, and apart from lemurs and lorises. In this taxonomic system, the two suborders of primates are instead Strepsirhini and Haplorhini. The reasoning behind grouping tarsiers with the formerly named anthropoids as a new group called haplorhines is that humans, apes, monkeys, and tarsiers all have shared derived features that indicate closer relation amongst them than with the lemurs and lorises which comprise strepsirrhines. Strepsirrhines are defined by features such as wet rhinarium, the presences of a tooth comb, a laterally flaring talus, and a grooming claw on the second digit of the foot. Tarsiers are distinct from the strepsirrhines in that they have a dry rhinarium, lack a tooth comb, as well as having certain skeletal and physiological traits that are more similar to the other haplorrhines. Furthermore, the extant haplorhines share a number of derived cranial features, including postorbital closure, a retinal fovea in their eyes, a reduced number of nasal conchae, a short, vertical nasolacrimal duct and the lack of a moist rhinarium, giving them the dry nose and continuous upper lip from which the name haplorhine derives. They also all have a hemochorial placenta and an inability to synthesize vitamin D. The tarsiers’ similarities to other prosimians are primitive features, like an unfused mandibular symphysis, molar teeth with high cusps, grooming claws on their second toes, multiple nipples, and a bicornuate uterus. In contrast, their similarities to anthropoid primates seem to be derived specializations indicative of a more recent common ancestor, a hypothesis that has been supported by genomic analysis. The taxonomic system with greater evidentiary support is, therefore, the phyletic division of haplorhines and strepsirrhines.
Tarsiers were initially categorized alongside lemurs and lorises, and apart from humans, apes, and monkeys. This original taxonomic system, known as the gradistic division, held that the two suborders of primates were Prosimii and Anthropoidea. Prosimians, which means “before apes”, were comprised of lemurs, lorises, and tarsiers, due to the perception that they represented grades of evolution. They were seen to possess many of the same traits, such as similar teeth, skull, and limb anatomy, to early, now extinct primates. These “primitive” features being shared amongst the three extant groups were believed to be evidence of close relation, and were thought to set them apart from the “more evolved” characteristics of anthropoids. The more recent categorization, known as the phyletic division, posits that tarsiers should actually be grouped alongside monkeys, apes, and humans, and apart from lemurs and lorises. In this taxonomic system, the two suborders of primates are instead Strepsirhini and Haplorhini. The reasoning behind grouping tarsiers with the formerly named anthropoids as a new group called haplorhines is that humans, apes, monkeys, and tarsiers all have shared derived features that indicates closer relation amongst them than with the lemurs and lorises which comprise strepsirrhines. Strepsirrhines are defined by features such as wet rhinarium, the presences of a tooth comb, a laterally flaring talus, and a grooming claw on the second digit of the foot. Tarsiers are distinct from the strepsirrhines in that they have a dry rhinarium, lack a tooth comb, as well as having certain skeletal and physiological traits that are more similar to the other haplorrhines. The superior taxonomic system is likely the phyletic division of haplorhines and strepsirrhines. The extant haplorhines share a number of derived cranial features, including postorbital closure to some extent, a retinal fovea in their eyes, a reduced number of nasal conchae, a short, vertical nasolacrimal duct and the lack of a moist rhinarium, giving them the dry nose and continuous upper lip from which haplorhine derives. In addition, haplorhines all have a hemochorial placenta and an inability to synthesize vitamin D. The tarsiers’ similarities to other prosimians are primitive features, like an unfused mandibular symphysis, molar teeth with high cusps, grooming claws on their second toes, multiple nipples, and a bicornuate uterus. In contrast, their similarities to anthropoid primates seem to be derived specializations indicative of a more recent common ancestor, a hypothesis that has been supported by genomic analysis.
The protein presenilin 1 is one subunit of a complex known as gamma-secretase. Presenilin 1 carries out the major function of the complex, which is to perform proteolysis on other proteins. The γ-secretase complex is best known for its role in processing amyloid precursor protein (APP), which is made in the brain and other tissues. Gamma-secretase cuts APP into smaller peptides, including soluble amyloid precursor protein (sAPP) and several versions of amyloid-beta peptide. Evidence suggests that sAPP has growth-promoting properties and may play a role in the formation of nerve cells in the brain both before and after birth. Alzheimer's disease patients with an inherited form of the disease have been found to carry mutations in the presenilin proteins or in the APP.
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