I would choose the mesolithic era is most important because Mesolithic means "Middle Stone Age. However, the prefix "meso-" in the word can mean "between," and this has been taken some scientists to refer to cultures in between a hunter-gathering mode and an agricultural mode. The Mesolithic era begins at the end of the Pleistocene epoch and the start of the Holocene, the most recent geologic epoch. Prior to the Mesolithic era, mile-thick continental glaciers covered most of Eurasia and North America. Any terrain north of 50 °N was essentially uninhabitable, until the ice melted around 11,000 years ago. Global temperatures increased, making life easier for humans worldwide. By the Mesolithic, humans had already spread across the entire world, except for Antarctica and a few remote islands. The Americas and Australia were fully colonized. The Mesolithic era was an unusual transition time between the Paleolithic and the Neolithic. Because the period was relatively short, Mesolithic artifacts are relatively hard to come by, consisting mainly of middens, or scrap-heaps. In coastal areas around the world, there are large shell middens dating to the Mesolithic era. In British Columbia, there is a midden several meters in depth which has been around for at least 10,000 years. Mesolithic cultures were about as advanced as you could get before establishing agriculture and cities. They hunted animals with a variety of bows and spears, and drove most of the world's megafauna to extinction. Like civilizations before them, they survived through a mix of hunting and gathering, although may have begun to intentionally plant the seeds of edible plants in fertile soils, pulling out the weeds.
Thursday, April 15, 2010
Blog 9 What geologic era do you think was the most important why?
I would choose the mesolithic era is most important because Mesolithic means "Middle Stone Age. However, the prefix "meso-" in the word can mean "between," and this has been taken some scientists to refer to cultures in between a hunter-gathering mode and an agricultural mode. The Mesolithic era begins at the end of the Pleistocene epoch and the start of the Holocene, the most recent geologic epoch. Prior to the Mesolithic era, mile-thick continental glaciers covered most of Eurasia and North America. Any terrain north of 50 °N was essentially uninhabitable, until the ice melted around 11,000 years ago. Global temperatures increased, making life easier for humans worldwide. By the Mesolithic, humans had already spread across the entire world, except for Antarctica and a few remote islands. The Americas and Australia were fully colonized. The Mesolithic era was an unusual transition time between the Paleolithic and the Neolithic. Because the period was relatively short, Mesolithic artifacts are relatively hard to come by, consisting mainly of middens, or scrap-heaps. In coastal areas around the world, there are large shell middens dating to the Mesolithic era. In British Columbia, there is a midden several meters in depth which has been around for at least 10,000 years. Mesolithic cultures were about as advanced as you could get before establishing agriculture and cities. They hunted animals with a variety of bows and spears, and drove most of the world's megafauna to extinction. Like civilizations before them, they survived through a mix of hunting and gathering, although may have begun to intentionally plant the seeds of edible plants in fertile soils, pulling out the weeds.
Blog 8 Give examples of the different types of natural selection. Give an example for each
The different types of natural selection are directional selection, disruptive selection, and Stabilizing selection. In directional selection, one extreme of the trait distribution experiences selection against it. The result is that the population's trait distribution shifts toward the other extreme. In the case of such selection, the mean of the population graph shifts. Using the familiar example of giraffe necks, there was a selection pressure against short necks, since individuals with short necks could not reach as many leaves on which to feed. As a result, the distribution of neck length shifted to favor individuals with long necks.In disruptive selection, selection pressures act against individuals in the middle of the trait distribution. The result is a bimodal, or two-peaked, curve in which the two extremes of the curve create their own smaller curves. For example, imagine a plant of extremely variable height that is pollinated by three different pollinators, one that was attracted to short plants, another that preferred plants of medium height and a third that visited only the tallest plants. If the pollinator that preferred plants of medium height disappeared from an area, medium height plants would be selected against and the population would tend toward both short and tall, but not medium height plants. Stabilizing selection is when natural selection works against the two extremes of a trait to make the population more uniform. For example, stabilizing selection might work on the birth weight of human babies to keep them at an intermediate weight, because babies that are too big or too small have less chance of being born healthy.