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Currently Homo Sapiens are the only surviving species of the genus Homo. There are two main models that explain how humans evolved. There is the, "out of Africa" model and the, "multi-regional" model. Both of those will be further explained.
Currently, the out of Africa model is the most widely accepted model of evolution. The out of Africa model proposes that humans evolved in Africa before migrating. The multi-regional model presents the idea that the evolution of Homo Sapiens took place in multiple locations over a long period of time.
The Out Of Africa Model proposes that humans evolved out of Africa before migrating. Genetic studies tend to support the Out of Africa Model. The highest levels of genetic variation in humans are found in Africa. The origin of modern DNA in the mitochondria has been tracked back to a single African woman who lived between 50,000 and 500,000 years ago, she is known as Mitochondrial Eve. Mitochondrial Eve was not the first woman on Earth at that time; she was simply the point from which all modern generations of humans appear to have grown.
The Multi-Regional model proposes that the evolution of humans took place in a number of locations over a long period of time. The Multi-Regional Model predicts that regional morphological patterns are stable; which reflects the absence of geological isolation. In order to test these assumptions, the incidence and distribution of the regional features proposed to characterize the evolution of Chinese and Javanese Homo Erectus into modern Chinese and Australian aborigines respectively were examined. The material that was studied were five recent populations and a fossil sample of anatomically modern Homo Sapiens from the site Afalou and Taforalt. These analyses showed first, that although the majority of the features studied present a regional pattern, this pattern does not always correspond to that proposed by the model; and second, that some of these features occur in other populations with a higher frequency. the lack of special resemblance between the North African fossils and recent Africans suggest high levels of population differentiation. These results indicate that these features do not support a multi-regional origin.
Around ten to twelve million years ago, the ancestor primate lineage split through speciation from one common ancestor into two major groups. The two lineages evolved separately into a variety of species we see today. Members of one of the groups were the early version of what we know today as the great apes. Modern great apes evolved from this lineage. The other group evolved differently. The other group became terrestrial, meaning they lived on land not trees.
From being quadrupeds this group evolved into bipeds. The size of their brain also increased. This group is the group that gave rise to modern humans. In Ethiopia, in the site Hadar which holds many fossils. Among the fossils was Australopithecus afarensis. In 1974, paleontologists found an almost complete skeleton of one specimen and named it Lucy, after the song by The Beatles, "Lucy in the Sky with Diamonds". This small female lived about 3.2 million years ago. An analysis of her femur bones showed that she used terrestrial locomotion. The famous paleoanthropologist Louis Leakey discovered Homo habilis (meaning handy man in Latin) in 1964. Homo habilis was the most ancient species of Homo ever found. Homo habilis appeared in Tanzania over 2.8 million years ago. They were estimated to be about 4.5 feet tall and 1.5 million years ago they became they extinct. They're different from Australopithecus because of the skull. The shape was round like the skull of a modern human.
Charles Darwin developed the theory of Natural Selection. In 1859, he brought the idea of natural selection to the attention of the world in his best-selling book, On the Origin of Species. Natural selection is the process through which populations of living organisms adapt and change. Individuals in a population are naturally variable, that means that they are all different in some ways. This variability means that some individuals have traits better suited to the environment than others. Individuals with adaptable traits are more likely to survive and reproduce. Through the process of natural selection, favorable traits are transmitted through generations.
Natural selection can lead to speciation. Speciation is a process by which one or more populations of a species become genetically different enough to form a new species. It is one of the processes that drives evolution, and it helps to explain the diversity of the Earth. Darwin chose the name natural selection to contrast with “artificial selection". Artificial selection is selective breeding that is controlled by humans. Darwin and other scientists of his day argued that a process much like artificial selection happened in nature, without any human intervention. He argued that natural selection explained how a wide variety of life forms developed over time from a single common ancestor.
Mutations are changed in the structures of DNA. If the environment changes rapidly, some species are not able to adapt fast enough through natural selection. Like breeders choose which of their animals will reproduce and thereby create the various breeds of domesticated dogs, pigeons, and cattle, nature effectively “selects” which animals will breed and creates evolutionary change just as breeders do. Much like breeders choose which of their animals will reproduce and create the various breeds of domesticated animals nature effectively “selects” which animals will breed and creates evolutionary change just as breeders do. Such natural selection, occurs as a result of the struggle for existence and the struggle for mating opportunities.
Whether natural selection has been operating and still operates in modern humans has been the subject of debate for a long time. Until recently, it was often said that human evolution has come to an end about 40,000-50,000 years ago. However new evidence that has been accumulated over the past decade suggests that natural selection has been operating in humans over the past few thousand years and a number of adaptations have also occurred recently. It has also been shown that height and BMI have been under selection in Europeans. Now with the availability of better healthcare, food, heating, and hygiene the number of selection pressures have greatly decreased. Selection pressures put pressure on us to adapt in order to survive in our environment. Selection pressure drives natural selection or survival of the fittest. Selection pressure is how we evolved into the species we are today. The present question is, now that we have fewer selection pressures with more help in forms of science and medicine, will evolution for humans stop completely? Genetic studies shown that humans are still evolving. To investigate which genes may be undergoing natural selection, researchers looked into the data produced by the International HapMap Project and the 1000 Genomes Project.
The International HapMap Project and the 1000 Genomes Project are both aimed to catalog genetic variation in DNA samples from individuals across the world. The majority of the cataloged human variation is characterized by single base changes. Also refered to as single nucleotide polymorphisms (SNPs). The location and frequency of these changes allows us to provide a list of regions in the human genome where genetic variation is most common. Patterns of reduced variations help scientists identify genes that may have recently been positively selected by natural selection. Genetic variations can be found by comparing the genomes of different people and looking to see where there are differences in the DNA sequence and where the genes are located in their genomes. When genetic variations presents a particular advantage and improve our fitness, the variation is more likely to survive and be passed on to future generations. Then becoming more common amongst the population. When this occurs a pattern can be found in the genomes of the population.
Our first ancestor, is a mere single-cell creature, our microbial Eve. We know that all extant living creatures derive from a single common ancestor, named LUCA. The Last Universal Common Ancestor. All living creatures are linked to a single-cell creature. The root to the complex branching tree of life. There were very possibly other life forms before LUCA. Scientists don't know what LUCA was, or when it thrived. Paleo-biologists have succeeded in mapping life's evolution from the bottom up. Instead of looking for bones and imprints in rocks to find LUCA; they looked at DNA. They are able to trace LUCA to a simple prokaryotic creature.
Evolution involves the gradual changes from simple to more complex forms. The evolution of modern humans from our ancestor is commonly considered to have four major steps: evolving terrestriality, bipedalism, encephalization (a large brain), and civilization. Stage one- between 4.-7 million years ago: Sahelanthropus, Orrorin and Ardipithecus all appeared in this time period. They are known as proto-hominins since it is debated whether they are our ancestors or not. Stage two- around 4 million years ago: the genus Australopithecus, our ancestors who are also bipedal appeared then. Stage three-around 2.7 million years ago: this is marked by the appearance of species classified under Paranthropus. However it is unsure whether this classifies as a separate genus. Stage four- between 2.5-1.8 million years ago: this stage consists of of species that all fall under the genus Homo, which consists of us and our immediate ancestors. Homo Habilis, the oldest is characterized by the usage of stone tools and a chimpanzee sized brain. Homo erectus and Homo egaster, the following members had double the brain size and were able to control fire. Then came along Homo heidelbergensis about 800,000 years ago and finally Homo sapiens appeared approximately 200,000 years ago.
There is another angle of approaching which is looking at four important steps or four important traits that were involved in human evolution. The first stage of human evolution-Terrestriality. Terrestriality refers to the adaptation of living on land. The next stage is bipedalism. Bipedalism is the ability to walk on two feet. This helped tremendously as free hands could now be used for labor. Long distance traveling became easier. It also resulted in changes to body parts and changes in bodily processes. The third stage is encephalization. An evolutionary adaptation involving an increase in brain size and complexity. It increased the possibility for social learning and learning of languages. The fourth and final stage is civilization. A society that is characterized by advanced culture and social development, and the making of tools is one example that is regarded as indicative of evolution.
I had three research questions. Where was the biggest change in humans through evolution? Are apes and humans related? Why are skulls so important to evolution?
Becoming bipedal led to creating selection pressure for a more elaborate brain to control more motor function and, process more incoming sensory information. Australopithecus afarensis was the first bipedal human.
The genomes of humans and apes differ by a little more than 1%. However this means that there are over 30 million point mutations. Some gene developments may lead to extinction, whilst others can cause innovation. This is enhanced by gene duplication. Simultaneously, the human/ape divergence will also be enhanced by cultural and learning effects. The two are heavily inter-related. Much of what makes us human is cultural, passed from generation to generation by learning. What makes humans different to apes is based on an evolutionary circle - genomes build bodies and brains, which create culture, which alters genomes. Humans and apes diverged from a common ancestor. Over time this evolutionary circle has increased the divergence, resulting in human uniqueness.
Brain growth encourages evolution. If human skulls never changed we wouldn't have been able to evolve. The strong jaw muscles of primates restricted the growth of skulls. This restriction disappeared about 2.5 million years ago with Homo habilis. Rapidly increasing brain size was a key feature that set humans apart from walking apes that lived 2.5 million years ago.
There are many theories in human evolution. There have been many steps through out human evolution. There are many complicated parts of evolution. Scientists still aren't 100% sure about how evolution really happened, but they have a good idea about it. Scientists have been studying evolution for many decades. Evolution is only a theory it is not a scientific law or fact.
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