Answer: there were few valleys 375 million years ago because during the acadian orogeny, the tectonic plates collided, forming mountains. This habitat was often snowy and cold at the summits of the mountains, and warmer and rocky in the foothills.
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From 1945–1955 the development of penicillin, which is produced by a fungus, along with streptomycin, chloramphenicol, and tetracycline, which are produced by soil bacteria, ushered in the antibiotic age.
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Populations from the Americas started from a founding population with a high frequency of the O allele
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Human blood type is determined by three different codominant alleles: IA, IB, and, which are named A (IA), B (IB), and O (i). Each person has two blood type alleles, i.e., one allele inherited from the mother and one from the father. The frequency of the O blood allele is very high in indigenous populations, and in Central and South American populations this allele may reach a frequency of 1 (100%). In consequence, the predominance of the O blood allele in Native American populations suggests that these populations descended from a founding population that had a high frequency of the O blood allele. A founder effect may even cause the fixation of one allele within a population, and this phenomenon is known to be associated with the loss of genetic variation.
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