kja@cbnewsd.att.com (krista.j.anderson) (06/30/90)
<> <> From: gary@cgdkarnak.cgd.ucar.edu (Gary Strand) > Of course, the damage that's been done this century, even with all the > earth-raping machines that there are, is minor compared to the changes First of all, I really hate it when people use the word "rape" to mean "take the goods and leave it ruined". "Exploit" might be more appropriate. > wrought by the natives of this continent between 50000 BCE (or whenever > they came over from Siberia) and the arrival of the Europeans. Hint: what > happened to the horses, the mammoth, and all the other megabeasts? Or the > forest that we now call the Great Plains? > > Sorry to tell ya, but humans have always engaged in massive environmental > modification. Sorry to tell ya, but the Great Plains were never a forest. When the earth was warmer and there was more liquid water, the Great Plains were an inland sea. Then the earth got colder with the ice ages. When the glaciers were covering half the Great Plains, down to latitudes of about 40 degrees, it was too cold for trees there and in the latitudes immediately south. After the most recent glacier began to recede in about 10,000 BC, it was still cool and trees began to grow in areas warm enough and moist enough for them. From about 5000 BC to about 2500 BC the climate became warm, in fact, hot, and grasses grew in the Great Plains. On the western Great Plains, it is too dry for forests because of the way the rain falls on the west side of the Rockies, since the winds move east there. The western Great Plains are a steppes region of short grasses that attracted the American bison. The eastern Plains get more rainfall and are the site of the genuine prairie, which is similar to a savannah. There the grasses were as tall as 7 feet high. The Plains bison did not venture into the tall grasses, but deer and other animals did. East of the Mississippi River are the Eastern Woodlands where there is plenty of rainfall for lush forests. An exception is the state of Illinois, where I now live. Here, strips of forest alternate with prairie. Illinois has important waterways and was densely inhabited by prehistoric peoples who practiced agriculture. It is possible that they cleared enough forests that prairie took over after farmlands were abandoned, but this is not known for sure. In the east, forests were able to replace agricultural fields, but not before the Forest bison had become extinct due to human intervention. As for the extinction of ice age mammals, please note that this was a world wide phenomenon, not just an American one. Was there a Pleistocene overkill done by humans? (actually by men, since males were the traditional hunters) We will never know for sure. We know that hunting by fire and cliff drives are age-old techniques that could have resulted in waste. But techniques of drying meat are also age-old, and in many cases the excess meat may have been preserved, making the hunt necessary less often. Another note is about the animals that became extinct as the Pleistocene came to an end, marked by the recession of the final glacier. I think it's possible that some of the animals had trouble adapting to the warming climate. Think of a mammoth. It is very shaggy and, well, ice-age looking. So is the American bison, but I can't think of many other very shaggy animals that have survived beyond the Pleistocene. (Well, the camel.) There was no similar extinction in South America, which did not undergo the same kind of climatic change. There were similar extinctions in northern Europe, which did, but not in southern Europe nor Africa, which didn't. On size, note Bergmann's rule that within species of warm-blooded animals, those that are larger will have less body surface per body mass, enabling the animals to better retain heat. Warm-blooded animals that are smaller will be better able to dissipate heat. (I read this in an archaeology book published in 1966, so if there is newer information, please let me know.) I don't know if Bergmann's rule applies across species, as there are many large animals in the tropics and small ones in cold places; it probably depends on the shape of the animals and on fat content. But it seems that several of the ice-age animals were quite large. Perhaps what was an advantage during the ice ages became a disadvantage toward the end of the Pleistocene. By the way, Bergmann's rule does apply to humans, and those whose ancestors were from equatorial climates tend to be shorter than those closer to the poles. Among Native Americans, studies of skeletons confirm that successive generations became taller in colder climates and shorter in warmer ones. (For example, a tall person in a hot climate might succumb more easily to a fever.) When I first read about Bergmann's rule, I wondered to myself, then why do I feel the heat more than my male friends seem to, even though I'm shorter, and why am I more comfortable in the cold? Well, it's because I have an extra layer of fat, as do most females. Ah, hah! That's when it hit me that I'd finally come upon a hypothesis to explain why female humans tend to be shorter than males. There is a social explanation that men were the traditional defenders and competed for women and were bred by mating patterns to be larger. But I think it has to do more with the fat issue, if not entirely the fat issue. More fat would give a person more volume per surface area, compensating for being shorter. So, are women shorter because they have more fat, or do they have more fat because they're shorter? Well, female athletes who are so active that they cannot store the normal amount of fat tend to stop menstruating, presumably because they have stopped ovulating. Maybe the extra energy needed for growing a fetus is taken from stored fat. Maybe the ripening of an ovum also requires some extra fat, so that a dearth of fat prevents ovulation which couldn't result in a success anyway, making it all work nicely together. So I think women need the extra fat for reproductive purposes and that being shorter gives them a proportion of body surface per volume that is comparable to the men in their family group. This would have been important in the tropical areas where humanoids first evolved. I would think it would be volume rather than mass that is an operant variable here. Fat weighs lighter than muscle. Men have more weight for their size to carry around, and perhaps this helps explain why women often have a lengthier endurance. As for why women tend to have less muscle mass, well, perhaps it is to keep the body volume down and still allow for the extra fat. Otherwise we would feel the heat too much. But to explain why women tend to be shorter in proportion to men, it must be noted that several human characteristics are adaptations to the cold. Homo erectus was unable to journey beyond the coastal regions of Africa, Europe and Asia. They tamed fire for us, made shelters and fashioned clothes, but could not produce the superior tools needed to venture north into the ice age cold. Not all Homo sapiens could survive the cold, either, but individuals with traits that were advantageous in cold weather survived to pass on their particular characteristics to the overall species. Homo sapiens became progressively taller, but females did not become proportionately taller (compared to men) because even the shorter females could survive better in the cold due to their extra fat. So, my hypothesis is that women must be shorter in order to cope with the heat, and men must be taller in order to cope with the cold and the fact that humans have coped with both heat and cold has emphasized sexual dimorphism. -- Krista A. HONOR Our Neighbors' Origins and Rights!