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Misconceptions about natural selection and adaptation
Misconceptions about natural selection and adaptation
Natural selection is a powerful process: it produces amazing adaptations (such as the "leaf-disguise" of the katydid shown below) and helps us understand much of what we observe in the natural world — but natural selection is often misunderstood. Frequently, the process is misconstrued as one that simply grants a species any trait that it might need for survival. However, as we will see, natural selection has its limitations, and many characteristics of organisms can be better understood with a more realistic view of the process.
Mimicry of leaves by insects is an adaptation for evading predators. This example is a katydid from Costa Rica.
To be an adaptation:
To be an adaptation:
- Is it heritable?
- Is it functional?
- Does it increase fitness?
- How did it first evolve?
Microevolution is simply a change in gene frequency within a population. Evolution at this scale can be observed over short periods of time — for example, between one generation and the next, the frequency of a gene for pesticide resistance in a population of crop pests increases. Such a change might come about because natural selection favored the gene, because the population received new immigrants carrying the gene, because some nonresistant genes mutated to the resistant version, or because of random genetic drift from one generation to the next.
The role of selective advantage in natural selection
The role of selective advantage in natural selection
Allopatric speciation is just a fancy name for speciation by geographic isolation, discussed earlier. In this mode of speciation, something extrinsic to the organisms prevents two or more groups from mating with each other regularly, eventually causing that lineage to speciate. Isolation might occur because of great distance or a physical barrier, such as a desert or river, as shown below.
Check for Understanding.
1. How could you determine if the mechanism of the evolution of a species is natural selection?
2. Explain why natural selection acts on a species and not individuals?
3. Why is diversity within a species essential for the process of natural selection?
Practice answering the following STAAR questions
Practice answering the following STAAR questions
Answers: A, C, B, A, D, H
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