An exercise in applied sensibility
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Evolution

Posted on Aug 10 2012

The theory of evolution maintains that the process or event responsible for initiating life on our planet occurred some 4 billion years ago in the waters (“The primordial soup”) of a very primitive earth, wherein inanimate molecules and unknown chemical processes combined to form biological entities. In the beginning, uni-cellular organisms divide and multiplied, then later combined to form multi-cellular creatures, gradually giving rise to the great diversity of plant and animal species and microscopic organism that constitutes life as we know it. Planet Earth in many ways is considered to be a living organism; the relationship between the many forms of life, and the various ways individual life forms interrelate with its environment, yields the ongoing process that continues to shape earth’s existence as we know it.

Over 90% of the great diversity of species that have ever existed on earth in its 4.6 billion year history is now extinct. Events causing extinctions are somewhat frequent throughout the history of our planet and are considered a fundamental consequence of the natural world. Extinction may afflict any species in a manner that is indifferent to the nature of its existence. Large and small-scale events causing extinction and their subsequent aftermath, in part, conduct the history of life on earth. Most noted is a cataclysmic event 65 million years bp (years before our present time). The most recent of 5 major mass extinctions marked the end of the Mesozoic era with the destruction of much of the existing life and saw the extinction of the dinosaurs. The reign of large land animals, also known as The Age of Reptiles, lasted for more than 150 million years. This extinction event also marks the beginning of our present era (the Cenozoic) wherein a variety of animals, plants, and insects survived to repopulate the planet.

Earth as we know it began to acquire its present form in and around the time dinosaurs became extinct. The resulting consequences of this particular mass extinction created the necessary conditions that, among other things, allowed for a greater diversification of primitive mammals (tiny mouse or shrew-like creatures) into various species, ultimately giving rise to a distinct population of primates from which humans would eventually evolve some 50 million years later. No complete scientific evidence or concinnity exists that maps man’s evolution from primitive mammals in clearly defined stages. What’s known is generated from biochemical (DNA) research on the lineage of earth’s primates; together with archeological evidence, research, and much debate, scholars are able to deduce the history of human evolution from their meticulous examination of fossils and artifacts of pre-history human and Hominid populations.

Ongoing inquiries estimate over 15 separate species of Hominids (human-like apes, and ape-like humans) make up our human family branch on the tree of life. The absence of conclusive evidence makes it difficult to pinpoint what actually sparked man’s evolutionary split from Tertiary primates; most researchers credit the separation to geologic events that accrued in East Africa’s Great Rift Valley, and the environmental pressures that ensued. Modern apes and humans have in common a group of ancestors who lived in Africa sometime between 5 million and 15 million years bp. That fact results in a mere 1.3% difference in the genetic makeup of humans, and that of modern day chimpanzees. Skeletal remains belonging to the earliest variety of hominids with prominent ape-like features are to be found exclusively in Africa, establishing the continent as the womb of early human development. Members of a much later variety of hominids eventually spread throughout Africa, and parts of the Eurasian continent around 2 million years bp, giving rise to various species of the genus Homo (Latin for man) that were distinguished mainly by an increase in brain capacity and a more human-like physique (shorter arms, fully opposable thumbs, reduced canine and molars, etc).

From Proconsul to Homo Sapiens Sapiens, the journey from primitive primates to modern humans is the subject of intense research. Up until the mid 1970’s, researchers assumed that the gradual development of a larger and more complex brain marked the transition from ape to man; today, new discoveries continue to reshape the specifics of human evolution. Studies in paleoanthropology suggest that among the few features identifying man with its pre-homo ancestors, while distinguishing hominids from other primates, is the ability to habitually walk upright on two legs. Bipedalism gradually became common practice for the earliest variety of hominids negotiating the open savannahs east of The Great Rift Valley, aiding the physical evolution of the human animal. Necessitated by the struggle to survive and adapt to the dwindling forest areas of the east African landscape, walking upright enabled a group of primitive primates to evolve a more successful terrestrial physique, with hands that are instrumental in gathering food, carrying loads more efficiently over longer distances. And to further aid their chances of survival, hominids acquired the capacity to fashion and utilize simple stone tools by around 2.5 million years bp; tools that are now used by anthropologists to help define the various stages of past stone age cultures. Other important physical changes theoretically credited to an upright posture, is the gradual repositioning of the spine, neck, head, larynx, etc. allowing for the ability to formulate the complex vocal sounds that would eventually compose human speech and language.

Though some of the early human species thrived for many thousands of years, what lead to their eventual extinction is unclear. Observations and ideas suggest that the inability of some specialized groups of hominids to adapt to sudden environmental changes might be among the primary causes.  Cannibalistic behavior; fierce competition for territory, food and other finite resources; the spread of diseases and epidemics, all are postulated as possible scenarios. Modern humans (Homo Sapiens Sapiens) represent the only extant species evolving from the population of hominids that inhabited earth for more than 5 million years. In the midst of our most recent ice age, about 100,000 years bp, environmental changes forced a substantial reduction in the human population that lasted some 10,000 years. By around 50,000 years bp, the human population was reduced to three distinct species:

Anatomically modern humans

Homo sapiens (a.k.a. Cro-Magnon man, Grimaldi man, etc. – evolved in Africa some time between 1 million years ago, and 200,000 years ago, eventually spreading throughout Eurasia and much of the world by 35,000 years bp),

Archaic Humans

Homo Neanderthalensis (survived over 200,000 years of evolution mainly in Europe, to a smaller degree in parts of Asia and the Middle East. Neanderthal’s ancestors migrated out of Africa circa 1.7 million years bp.)

Homo Erectus (whose species survived over 1.8 million years of evolution, is a widely traveled hominid, second only to modern humans. Erectus existed mainly in Africa; Small populations settled in parts of Asia and parts of Europe –closely related to, or possibly the forbearers of Homo sapiens – Ongoing debates seek to determine if Homo erectus is the common ancestor of modern humans and other Homo species).

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