This is an open access article distributed under the Creative Commons Attribution License , which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Abstract Horizontal gene transfer has proved to be relevant in eukaryotic evolution, as it has been found more often than expected and related to adaptation to certain niches. A relatively large list of laterally transferred genes has been proposed and evaluated for the parasite Entamoeba histolytica. The goals of this work were to elucidate the importance of lateral gene transfer along the evolutionary history of some members of the genus Entamoeba, through identifying donor groups and estimating the divergence time of some of these events. In order to estimate the divergence time of some of the horizontal gene transfer events, the dating of some Entamoeba species was necessary, following an indirect dating strategy based on the fossil record of plausible hosts. The divergence between E. We estimated times for 22 transferences; the most recent occurred Indeed, the acquisition of genes through lateral transfer may have triggered a period of adaptive radiation, thus playing a major role in the evolution of the Entamoeba genus. Introduction Entamoeba genus is formed by morphologically similar amoebas; most of them are intestinal parasites that can infect several hosts [ 1 ]. Entamoeba histolytica is one of the most important intestinal protozoan parasites in humans causing amoebic colitis; they can also invade the liver causing amoebic liver abscess.
Rocks, Fossils and Time – PowerPoint PPT Presentation
The older, Late Proterozoic sedimentary sequence is comprised of the Grand Canyon Supergroup which consists of the Chaur Group, the Nankoweap Formation, the Unkar Group, and the Sixtymile Formation, and is only found in isolated patches along the main Colorado River corridor and some of its major tributaries Figure 2. Beginning about 1, million years ago and lasting about million years during the Late Proterozoic Era , approximately 13, feet of sediments and lava were deposited in coastal and shallow marine environments.
Basin-and-Range style crustal deformation beginning about million years ago lifted and tilted these rocks. Subsequent erosion removed these tilted layers from much of the Grand Canyon region leaving only wedge-shaped remnants preserved in large graben structures Figure 2 , mainly observed in the eastern parts of the canyon.
These mudstones, sandstones, and limestones are widely distributed in the canyon, but total a mere 2, and 5, feet thick by comparison with Proterozoic rocks.
In order to estimate the divergence time of some of the horizontal gene transfer events, the dating of some Entamoeba species was necessary, following an indirect dating strategy based on the fossil record of plausible hosts.
One of the Olduvai hominins, OH 24, seems anatomically similar to Australopithecus in having prominent cheekbones and a flat nasal region. Such hollowing of the face is characteristic of some South African australopiths but is not seen in later Homo. The facial skeleton of ER is large relative to the braincase, and it shows flattening below the nose —Australopithecus-like features.
The walls of the nasal opening, however, are slightly everted, and there is at least an indication that the nose stands out in more relief than would be expected in australopiths. The face of ER is even more modern. The front teeth of H. The jaw itself may be quite heavily constructed like that of gracile australopiths. This is the case for OH 7 and also for at least one specimen from Koobi Fora.
Other jaws are smaller but still robust in the sense of being thick relative to height. For example, the mandible of OH 13 is similar in many respects to that of H. Only a few other skeletal parts have been discovered. Some limb bones from Olduvai and Koobi Fora have been grouped tentatively with H. These fossils, however, are not associated with any teeth or skulls, and it is probably not appropriate to use them as the basis for describing early Homo. One individual for which body parts are more fully represented is OH
Dating Fossils – How Are Fossils Dated?
A Fossils are the remaining parts and hints of old life forms. A bunch of fossil ammonites, a wiped out cephalopod. While there is no characterized date, ordinarily something must be more established than 10, years to be viewed as a fossil.
FOSSILS AND FOSSILIZATION Introduction This week you will begin working on the fossil notebook. It will be due in 4 weeks and is worth 25% of your grade. This is an Trace fossils – Any indirect evidence of an organism. Records behavior of organism. ex: tracks, trails, burrows, coprolites (fossilized feces), gastroliths (gizzard stones), may.
Fossil and fossilization Photo by: Bastos A fossil is the remains or traces of a once-living plant or animal that was preserved in rock or other material before the beginning of recorded history. The term also is used to describe the fossil fuels oil, coal, petroleum, and natural gas that have been formed from the remains of ancient plants and animals. It is unusual for complete organisms to be preserved.
Fossils usually represent the hard parts, such as bones or shells of animals and leaves, seeds, or woody parts of plants. Fossils occur on every continent and on the ocean floor. Through paleontology the scientific study of fossils , it is possible to reconstruct ancient communities of living organisms and to trace the evolution of species. Fossils of single-celled organisms have been recovered from rocks as old as 3.
Animal fossils first appear in rocks dating back about 1 billion years.
Oldest Homo sapiens fossils discovered in Morocco
January 7, ] volution is the cornerstone of modern biology. It unites all the fields of biology under one theoretical umbrella. It is not a difficult concept, but very few people — the majority of biologists included — have a satisfactory grasp of it. One common mistake is believing that species can be arranged on an evolutionary ladder from bacteria through “lower” animals, to “higher” animals and, finally, up to man.
Mistakes permeate popular science expositions of evolutionary biology.
The Guadalupian-Lopingian Boundary (GLB) is defined by the first occurrence of the conodont species Clarkina postbitteri postbitteri and currently interpreted to be ± Ma .
Fossil record The fossil record is the record of life on Earth as it is preserved in rock as fossils. The fossil record provides evidence of when and how life began on the planet, what types of organisms existed and how long they persisted, how they lived, died, and evolved, and what the climate was and how it changed. The fossil record also has allowed scientists to correlate rocks on a worldwide basis and to determine the relative ages of rock formations.
Fossils record life by preserving remains of organisms. A fossil is a rare thing. Most organisms decay and disappear quickly after dying. Of the tiny minority of organisms that do become preserved as fossils, an even smaller fraction survives the geologic cycle to become exposed and visible. As a result the fossil record is incomplete; there is no record of most organisms that probably lived and died.
The oldest Homo sapiens bones known date to about , years ago, but the new analysis shows these bones are surprisingly old: Workers discovered the bone site in the s. The doctor turned the skull over to scientists. It was a puzzling bone. Complicating matters still, the quarry miners took few detailed records of where they found the bones.
Indirect dating is the age of an object in comparison to another, not an exact age, while direct dating is a technique used to date materials such as rocks or carbon, also known as radioactive dating.
See Article History Australopithecus, Latin: The various species of Australopithecus lived during the Pliocene 5. As characterized by the fossil evidence, they bore a combination of human- and apelike traits. Like humans, they were bipedal that is, they walked on two legs , but, like apes, they had small brains. Their canine teeth were small like those of humans, but their cheek teeth were large. Artist’s rendering of Australopithecus afarensis, which lived from 3. Other australopiths include Sahelanthropus tchadensis 7—6 mya , Orrorin tugenensis 6 mya , Ardipithecus kadabba and Ardipithecus ramidus 5.
Remains older than 6 million years are widely regarded as those of fossil apes.
What is a Fossil:
Genetics[ edit ] One of the strongest evidences for common descent comes from gene sequences. Comparative sequence analysis examines the relationship between the DNA sequences of different species,  producing several lines of evidence that confirm Darwin’s original hypothesis of common descent. If the hypothesis of common descent is true, then species that share a common ancestor inherited that ancestor’s DNA sequence, as well as mutations unique to that ancestor.
More closely related species have a greater fraction of identical sequence and shared substitutions compared to more distantly related species. While on board HMS Beagle , Charles Darwin collected numerous specimens, many new to science, which supported his later theory of evolution by natural selection. The simplest and most powerful evidence is provided by phylogenetic reconstruction.
fossil d is an original fossil in which the animal has been preserved by falling in a tar pit. (a) Explain some differences in the way fossils j and d were formed.
Early history[ edit ] In Ancient Greece , Aristotle BCE observed that fossils of seashells in rocks resembled those found on beaches — he inferred that the fossils in rocks were formed by living animals, and he reasoned that the positions of land and sea had changed over long periods of time. Leonardo da Vinci — concurred with Aristotle’s interpretation that fossils represented the remains of ancient life.
Steno argued that rock layers or strata were laid down in succession, and that each represents a “slice” of time. He also formulated the law of superposition, which states that any given stratum is probably older than those above it and younger than those below it. While Steno’s principles were simple, applying them proved challenging. Over the course of the 18th century geologists realized that: Sequences of strata often become eroded, distorted, tilted, or even inverted after deposition Strata laid down at the same time in different areas could have entirely different appearances The strata of any given area represented only part of Earth’s long history The Neptunist theories popular at this time expounded by Abraham Werner — in the late 18th century proposed that all rocks had precipitated out of a single enormous flood.
It has been said[ by whom? This theory, known as ” Plutonism", stood in contrast to the"Neptunist” flood-oriented theory. Formulation of geologic time scale[ edit ] The first serious attempts to formulate a geologic time scale that could be applied anywhere on Earth were made in the late 18th century.
Briggs–Rauscher oscillating reaction
Before Darwin[ ed[ edit ] word homo, the name of the biological genus to which humans belong, is Latin for “human”. It was chosen originally by Carl Linnaeus in his classification system. The word “human” is from the Latin humanus, the adjectival form of homo. Darwin[ ed[ edit ] possibility of linking humans with earlier apes by descent became clear only after with the publication of Charles Darwin ‘s On the Origin of Species , in which he argued for the idea of the evolution of new species from earlier ones.
Darwin’s book did not address the question of human evolution, saying only that “Light will be thrown on the origin of man and his history.
Sep 25, · All fossil dating is very indirect, but the Bible account is direct, and the genealogies are there to guide us. Click to expand The years may be true but the hypothesis that Earth is billions of years old may also be true from astronomical observations and computer simulations (no radio-carbon dating involved!).
Radioactive dating is not important in providing evidence for evolution. Radioactive dating can only provide indirect evidence for evolution. Radioactive dating can provide supporting evidence for evolution. The easiest form of radioactive dating to understand is Carbon Carbon 14 with a half life of 5, years can only be used to date the most recent fossils. Also any erosional loss of material or slight contamination would throw off any values. Fossils often have no carbon in them at all.
What is the difference between direct dating and indirect dating in archaeology?
Due to experimental difficulty, it attracted little attention and was unsuitable as a demonstration. Belousov in the Soviet Union discovered the Belousov—Zhabotinsky reaction, but it met with skepticism, because such oscillatory behaviour was unheard of up to that time. It was verified by A. Zhabotinsky, also in the USSR, who in published his research.
Scientists use two kinds of dating techniques to work out the age of rocks and fossils. The first method is called relative dating. This considers the positions of the different rocks in sequence (in relation to each other) and the different types of fossil that are found in them.
Homologous organs are those, which have the same basic structure, but different functions. For example, an examination of the forelimb skeleton in different groups of land vertebrates reveals that the number and arrangement of bones remains the same. However, the forelimbs are used for diverse functions in different groups. In frogs, forelimbs are not generally used for locomotion or swimming. In a lizard, forelimbs are as prominently used for locomotion as the hind limbs.
In birds, they are modified into wings. In mammals, they show further diversity. A bat’s patagium, a man’s arm, a horse’s fore leg and a whale’s flippers serve totally different functions, but possess the same basic structure. Such a structural homology indicates a probable common ancestry for the different groups.