The everyday meaning of "adaptation" refers to a change that occurs in a single individual's lifetime, while the evolutionary meaning refers to a trait that has developed via natural selection over many generations. An evolutionary adaptation is also defined strictly in terms of relative reproductive fitness, while the everyday meaning can refer to changes that do not necessarily affect reproduction.
a. The four postulates are, briefly: variation exists, the variation is heritable, survival & reproduction are not equal, and survival and reproduction are not random. In the snapdragon experiment, if there had been no variation, all flowers would have been the same color. If variation had not been heritable, the colors of the best-reproducing plants would not have been passed to their offspring. If there had not been unequal survival and reproduction, all plants would have attracted equal numbers of bees, and produced equal numbers of seeds. If survival and reproduction had been random, some plants would have had more bee visits and produced more seeds than other plants, but the difference would not be related to plant color. In any of these four cases, the snapdragon population would not have evolved. b. If the four postulates are true, a population is virtually certain to evolve, unless selection is extremely weak and genetic drift is very strong. Since the four postulates are almost always true, virtually all populations are probably evolving today, at least some genetic loci.
a. If bill depth was not variable, Figure 3.9 would show one skinny, high bar - all finches would have had exactly the same bill depth. b. If bill depth was not heritable, the two graphs in Figure 3.13 would look the same. The1978 post-drought birds would still have the same average bill depth as the 1976 birds (even though the 1978 chicks had thicker-billed parents). The population would not have evolved. c. In Figure 3.10, the strongest overall trend is clearly that thick-billed parents have thick-billed chicks. This demonstrates heritability of beak depth. But the fact that one line is slightly higher than the other shows that a small part of the variation in beak depth is not heritable. Parents with a given average bill depth had slightly thicker-billed chicks in 1978 than in 1976. This is probably due to a slight environmental effect on beak depth.
The claim that the vanished finches probably died of starvation is certainly reasonable, given the data in Figure 3.11, and the absence of obvious other causes such as increased predation or disease. The graphs in Figure 3.11 show that most small, soft seeds disappeared between about July and October of 1976, the same time that the bird population began to decline. Seeds were still abundant at first, but they were predominantly large seeds. Then, even the large seeds began disappearing, and the bird population continued to decline sharply. The birds did not all die instantaneously because it takes time for an animal to starve to death, and some individuals were likely able to scratch for the few remaining small seeds for several months before succumbing.
Many answers are possible. Though it may be "just" microevolution, the shape of a bird's bill is not a minor feature for the bird-it is the bird's one and only food-handling tool. Furthermore, microevolution and macroevolution are not a dichotomy-macroevolution is simply microevolution carried out for a long time. The changes that most laypeople would consider "macroevolution" typically require hundreds of thousands of years to evolve, so it is not logical to expect to observe them in a single field study. Evolutionary biologists generally regard long-term studies of microevolution as highly informative for learning how natural selection happens in a natural environment, and for a close-up look at the causes of small changes that, eventually, can add up to macroevolution.
Many answers are possible. A first step would be to identify some traits that affect the plant's survival or reproduction if rainfall changes, such as drought tolerance or resistance to root rot. We would then want to measure current variability in those traits, carefully assess the heritability of that variation, and explore the genetic and developmental underpinnings of the traits as much as possible. Over time, we would measure survival and reproduction (seed set, pollinator visits) of all the plants on the island. We would, of course measure changes in the amount of rainfall, and also keep an eye on other environmental factors that might affect our results. Over many years, we would inspect our growing dataset to see if certain genotypes were changing in abundance due to differences in survival and reproduction, and if these changes can reasonably be linked to rainfall.
Krontiris is referring to "group selection": selection of a trait that is detrimental to the individual carrying the trait, but that is favorable to other members in the group. Unless the individual in question is closely related to other members of the group (kin selection - see chapter 12), this cannot happen. Natural selection eliminates traits that are detrimental to the individual carrying the trait. Even if others in the group would benefit, the trait will quickly be eliminated from the population.
Three major objections to Darwin's theory were: there is not enough variability for evolution to continue for very long; new traits would disappear by "blending" with other traits; and, the earth's temperature implies that the earth is too young for evolution to have occurred. These were resolved by the discoveries of mutation, genes, and radioactivity, respectively. The message is that a theory should not be discarded if it cannot answer all questions, especially if it is clearly better than all alternative theories ("better" meaning that it agrees with more data, makes more successful predictions, and has fewer unanswered questions). The unanswered questions should instead be regarded as topics deserving intensive research.
The answer to this question is left to the reader.
a. The "irreducible complexity" argument states that if a complex biological process or entity cannot function without the presence of many interdependent parts, then that process cannot have evolved. This is not a logical argument, because complex processes do not evolve all in one step. Specifically, they can evolve in two stages, first slowly accumulating the different parts (each new part being, at first, helpful but not essential), and only later refining the process so that the parts become interdependent. The argument does not apply to the eye or the flagellum in any case, since some types of simplified eyes and flagella do, in fact, function. Though they do not function as well as an advanced eye or flagellum, the simplified versions are clearly more useful than having no eyes or no flagella. b. The major logical flaw with the "argument from personal incredulity" is that it can be due simply to ignorance or lack of imagination. Furthermore, it tends to discourage research into interesting questions.
The answer to the first question is left to the reader. As for the second question, any objection to evolutionary theory on the grounds that it occurred in the past and/or is not directly observable must, logically, also apply to all other theories regarding processes that occurred in the past or are not directly observable. This includes all historical sciences, (including geology, astronomy, and archeology), as well as sciences that infer the existence of particles that cannot be observed directly (such as particle physics today, and, in the past, cell theory and germ theory).
The answer to this question is left to the reader.
The answer to this question is left to the reader.
