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All of the changes, diversifications, and extinctions that happened over the course of life's history are the patterns of overall evolution. Evolution of life has been taking place for about 3.8 billion years of time. When we view macroevolution - the large-scale evolutionary history of life, it encompasses the grandest trends and transformations in evolution, such as the origin of mammals and the radiation of flowering plants.
Is the evolution of species a higher progression, improvement to more complex, more intelligent life as is often thought?
From a biological point of view the word 'progression' is better suited than progress. We need to remember certain things. Firstly, there are multiple branches possible at each and every stage of evolution. Speciation does not intend to convey the dieing out of one inferior species giving way to superior ones. Species adapt to the conditions available in their environment. Some older and simple species live on quite effectively. The scorpion, is one of the more primitive invertebrate which has lived successfully for millions of years, it can withstand heat and nuclear radiation levels that would easily kill man!
Secondly, at the macroevolution level the same evolutionary process of mutation, gene flow, genetic drift and natural selection are the causes for evolution. The evolutionary process of nature has resulted in every organism reaching a stage of evolution by a natural and coercive process. The same process has brought man to the stage of a human being and considers him a specific kind of species as distinct from other species. In actual fact, there is no real 'progress' in the idea of evolution. It simply implies the generation and shaping of diverse life forms by environmental selection. The only progressive trend in evolution seems to be that more and more complex body designs have emerged over time.
Human evolution concerns itself with the emergence of humans as a distinct species. Undoubtedly, there are special features possessed by 'Homo sapiens' considered to be at the top of the evolutionary ladder but science has become fully committed to finding purely biological explanations for the origin of these features.
The term "human", in the context of human evolution, refers to the genus Homo, but studies of human evolution usually include other hominins, from whom apes and homsapiens speciated but are now extinct. Homo sapiens ("sapiens" means wise or intelligent) have lived from about 250,000 years ago to the present. Homo sapiens showed a distinct cranial expansion from the earlier species it speciated from, the Homo erectus. Ther is now direct evidence that all homosapeans originated in Africa and migrated all over world (there is little evidence that this speciation occurred elsewhere). While some groups stayed in Africa, others spread from Africa to West Asia, then to Central Asia, Eurasia, South Asia, East Asia. They ventured down the islands of Indonesia and the Philippines and crossed over to Australia. They finally crossed the Bering land bridge to the Americas.
There is a great diversity in human types, with varied forms and features across the planet. We see brown, white, black, skin types, tall Americans and Europeans, smaller Asians, and pigmies, Nordic, Afro, Asian, Mongoloid, features. Are we all one species or have these groups developed separately? The genome project, a genetic study into the origin of different human races has shown that human beings are one big family! They are highly genetically homogenous, meaning that the DNA of individual Homo sapiens is more alike than usual for most species.
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