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| If natural selection, if "survival of the fittest," is the case, why aren’t all creatures as fast as a cheetah, as large as an elephant, and as strong as a bear? Ans: Natural selection works on selecting advantageous traits when there is (1) variation in a population and (2) competition for strategic resources. Natural selection only works to produce a species that is adapted for its environment, NOT the "ultimate" species. For example, a giraffe's long neck makes it ideal for the savannah where trees are scare and leaves are high off the ground, but giraffes would not do well in a tundra environment where all food is near the ground. Likewise, a cheetah is well adapted to an environment where large game is plentiful if it can be caught in large open areas, but this investment in lean, fast muscle-mass would be a waste if food was more readily available from catching fish in water, as some bears do. How does creationism explain how there are some species alive today that do not appear deep in the fossil record, whereas there are some species in the fossil record, such as dinosaurs, that are not alive today? Ans: Creationism uses catastrophism to explain the discrepancy. That is, creationists rely on Biblical accounts of destruction, such as the flood, and of creation. The evolutionary approach is to consider that the processes of natural selection and mutation are going on today just as they have in the past and that life is constantly changing. When and how do new species form? Ans: New species form when a population becomes isolated and undergoes genetic change through mutation or genetic drift; eventually enough changes have accumulated so that the new species is no longer sexually compatible with the old species. Speciation is prevented if gene flow continues between populations. Why do some characteristics such as eye color vary from parent to child, if children inherit their genes from their parents? Ans: Gregor Mendel discovered that dominant and recessive genes control some traits. The dominant forms never go away, but the recessive forms can also be present genetically in the genotype, though they may not express themselves physically in the phenotype. Additionally, Mendel discovered that traits are controlled by at least two alleles, and through the law of Independent Assortment and Recombination he showed that a child only receives one, not both, of the alleles from each parent. How can sickle-cell anemia, a fatal childhood genetic disease, continue to be prevalent if natural selection is operating? Ans: The allele for sickle cell anemia, HbS, is a recessive gene. If an individual is homozygous for the allele, it is probably fatal. But if an individual is heterozygous, that person has some immunity from malaria. Because malaria is so prevalent and destructive in parts of Africa, India, and the Mediterranean, the gene has been maintained there through natural selection despite the problems in the homozygous form. |