Retrace the history of primate evolution from early primates to monkeys, apes an

Question

Retrace the history of primate evolution from early primates to monkeys, apes and hominins. When did some ofthe significant divergences occur (such as between the prosimians and the monkeys or between the chimps and hominins)? What was happening with the continents and the major climatic conditions during these times?What are the major species (including the extinct species) along the human lineage after the split with the chimps and bonobos? Where did many of these events occur on the globe and when?

Explanation / Answer

Transitional primate-like creatures were evolving by the end of the Mesozoic Era (ca. 65.5 million years ago). At that time, the world was very different from today. The continents were in other locations and they had somewhat different shapes. North America was still connected to Europe but not to South America. India was not yet part of Asia but heading towards it at a surprisingly rapid rate of nearly 8 inches (20 cm.) per year. Australia was close to Antarctica. Most land masses had warm tropical or subtropical climates. The flora and fauna the end of the Mesozoic Era would have seemed alien since most of the plants and animals that are familiar to us had not yet evolved. Large reptiles were beginning to be replaced by mammals as the dominant large land animals. Among the mammals, there were a few archaic egg-layers (monotremes) like the ancestors of the platypus and echidna. There were larger numbers of pouched opossum-like mammals (marsupials). The few placental mammals that existed at that time mainly consisted of the Insectivore ancestors of primates. Most of the mammal species were small, ranging from about the size of a mouse up to a medium size domesticated dog. The large grass-eating placental mammals, such as cattle and wildebeest, were absent as were the vast grasslands that would later develop. Rodents and seed-eating birds were also absent. The great proliferation of flowering plants had not taken place yet. However, forests of broad-leafed trees were developing over much of the earth.

There are about 400 species of this, which include prosimians (lemuars, bushbabies monkeys and apes). They all share a number of general features that distinguish them from other mammals. Including nails rather than claws and eyes on front of the face instead of the side allowing stereoscopic (three dimensional vision). Most of these also have some form of opposable thumb (a thumb that can touch the fingertips of the same hand; contrast the motion of your thumb with that of your no opposable big toe. As recently as 30 years ago, the canopy of the tropical forest was regarded as an easy place for apes, monkeys and prosimians to find food. Extending an arm, it seemed, was virtually all our primate relatives had to do to acquire a ready supply of edibles in the form of leaves, flowers, fruits, and other components of trees and vines. Since then, efforts to understand the reality of life for tree dwellers have helped overturn that misconception. Selective pressures also favored considerable enhancement of the visual apparatus (including depth perception, sharpened acuity and color vision), thereby helping primates travel rapidly through the three-dimensional space of the forest canopy and easily discern the presence of ripe fruits or tiny, young leaves. And such pressures favored increased behavioral flexibility as well as the ability to learn and remember the identity and locations of edible plant parts. Foraging benefits conferred by the enhancement of visual and cognitive skills, in turn, promoted development of an unusually large brain, a characteristic of primates since their inception.

The period of human evolution has coincided with environmental change, including cooling, drying, and wider climate fluctuations over time. How did environmental change shape the evolution of new adaptations, the origin and extinction of early hominin species, and the emergence of our species, Homo sapiens (‘Hominin’ refers to any bipedal species closely related to humans – that is, on the human divide of the evolutionary tree since human and chimpanzee ancestors branched off from a common ancestor sometime between 6 and 8 million years ago.) One important line of evidence is the record of oxygen isotopes through time. This record of 18O, or oxygen stable isotopes, comes from measuring oxygen in the microscopic skeletons of foraminifera (forams, for short) that lived on the sea floor. This measure can be used as an indicator of changing temperature and glacial ice over time. There are two main trends: an overall decrease in temperature and a larger degree of climate fluctuation over time. The amount of variability in environmental conditions was greater in the later stages of human evolution than in the earlier stages. Overall, the hominin fossil record and the environmental record show that hominins evolved during an environmentally variable time. Higher variability occurred as changes in seasonality produced large-scale environmental fluctuations over periods that often lasted tens of thousands of years. The variability selection hypothesis implies that human traits evolved over time because they enabled human ancestors to adjust to environmental uncertainty and change. The hypothesis addresses the matter of how, exactly, adaptability can evolve over time. Ancient hominin remains have been found in a variety of different habitats. While some hominins, such as Orrorin tugenensis and Ardipithecus ramidus have been found in wooded habitats, others such as Sahelanthropus tchadensis were found associated with diverse types of vegetation within a small geographic area. Reconstructions of the ancient habitat of Ardipithecus ramidus at two different Ethiopian sites suggest that this species occupied both wooded areas (the Aramis site) and wooded grasslands in which grazing animals predominated (the Gona site). Australopithecus anamensis has been found at Kanapoi and Allia Bay, Kenya, in association with another type of mosaic – an open savanna with low trees and shrubs, but with both grasslands and gallery forests nearby.

It was unclear, however, which of the hundreds of extinct ape species found during the nineteenth and twentieth centuries in Africa, Europe and Asia, dating from the period 10 million to 35 million years old, gave rise to the human lineage. These fossils together constrain the age of the gorilla versus chimpanzee-human split to between 8 and 10 million years ago, well within the range of estimates from molecular clocks. Alternatively, if the detractors are correct, and Sahelanthropus, Orrorin and Ardipithecus turn out not be human, then there’s a huge chunk of time, 4-6 million to be precise, for these events to occur, and an even bigger gap in knowledge of our past. Scientists estimate that our planet, Earth, formed around 4600 million years ago. The oldest rocks dated so far are from the Acasta Gneiss Complex near Great Slave Lake, Canada with an age of about 4030 million years. The Isua Supracrustal rocks in West Greenland are dated at about 3700 to 3800 million years old. The best age estimate for the Earth's final formation is about 4540 million years ago, based on data from the Canyon Diablo meteorite. In addition, mineral grains called zircon from sedimentary rocks from west-central Australia have recently been reported with an age of about 4400 million years. This was the so-called "Hadean Period" from 4600 - 3800 million years ago. During this period the heavier molten iron sank to the middle of the newly forming Earth, to become the core. The lighter material rose to the surface, the lightest of all becoming the crust on the surface. There was also an outgassing of volatile molecules such as water, methane, ammonia, hydrogen, nitrogen, and carbon dioxide, which formed the early atmosphere of the Earth. The initial steam atmosphere was made of water from comets and hydrated minerals from volcanic eruptions. Rain fell into proto-ocean about 4300 to 4400 million years ago. All terrestrial planets are thought to have had a similar process in their early histories.

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