Examples of adaptation by natural selection HMS Beagle, During his voyage on the Darwin observed a curious pattern of adaptations among several species of finches (now called Darwin's finches) that live on the Galapagos Islands. Several traits of finches went through drastic changes in response to changes in their environment. One example is beak depth: There was huge variation in beak depth among finches on the island; it affected the birds' survival and adaptation to local environmental changes. During a drought, finches with deeper beaks were more likely to survive than finches with shallow beaks (which were at a disadvantage because it was harder for them to crack larger and harder seeds). Parents and offsprings had similar beak depths. Through natural selection, average morphology (an organism's size, and composition) of the bird population changed so that birds became better adapted to their environment. Benefits and disadvantages of evolution Individual Selection Adaptation results from competition among individuals, not between entire populations or species. Selection produces adaptations that benefit individuals. Such adaptation may or may not benefit the population or species. In the case of finches' beak depth, selection probably does allow the population of finches to compete more effectively with other populations of seed predators. However, this need not be the case. Selection often leads to changes in behavior or morphology that increase the reproductive success of individuals but decrease the average reproductive success and competitive ability of the group, population, and species. Example of conflict between individual and group interests: All organisms in the population produce many more offspring than are necessary to maintain the species. A female monkey may, on average, produce 10 offspring during her lifetime. In a stable population, perhaps only two of these offspring will survive and reproduce. From the point of view of the species, the other eight are a waste of resources. The species as a whole might be more likely to survive if all females produced fewer offspring. The idea that natural selection operates at the level of the individual is a key element in understanding adaptation. Directional Selection Instead of a completely random selection of individuals whose traits will be passed on to the next generation, there is selection by forces of nature. In this process, the frequency of genetic variants for harmful or maladaptive traits within the population is reduced while the frequency of genetic variants for adaptive traits is increased. Natural selection, as it acts to promote change in gene frequencies, is referred to as directional selection. Stabilizing Selection Finches' beaks (Example)
Examples of adaptation by natural selection During his voyage on the HMS Beagle, Darwin observed a curious pattern of adaptations among several species of finches (now called Darwin's finches) that live on the Galapagos Islands. Several traits of finches went through drastic changes in response to changes in their environment. One example is beak depth: There was huge variation in beak depth among finches on the island; it affected the birds' survival and adaptation to local environmental changes. During a drought, finches with deeper beaks were more likely to survive than finches with shallow beaks (which were at a disadvantage because it was harder for them to crack larger and harder seeds). Parents and offsprings had similar beak depths. Through natural selection, average morphology (an organism's size, and composition) of the bird population changed so that birds became better adapted to their environment. Benefits and disadvantages of evolution Individual Selection Adaptation results from competition among individuals, not between entire populations or species. Selection produces adaptations that benefit individuals. Such adaptation may or may not benefit the population or species. In the case of finches' beak depth, selection probably does allow the population of finches to compete more effectively with other populations of seed predators. However, this need not be the case. Selection often leads to changes in behavior or morphology that increase the reproductive success of individuals but decrease the average reproductive success and competitive ability of the group, population, and species. Example of conflict between individual and group interests: All organisms in the population produce many more offspring than are necessary to maintain the species. A female monkey may, on average, produce 10 offspring during her lifetime. In a stable population, perhaps only two of these offspring will survive and reproduce. From the point of view of the species, the other eight are a waste of resources. The species as a whole might be more likely to survive if all females produced fewer offspring. The idea that natural selection operates at the level of the individual is a key element in understanding adaptation. Directional Selection Instead of a completely random selection of individuals whose traits will be passed on to the next generation, there is selection by forces of nature. In this process, the frequency of genetic variants for harmful or maladaptive traits within the population is reduced while the frequency of genetic variants for adaptive traits is increased. Natural selection, as it acts to promote change in gene frequencies, is referred to as directional selection. Stabilizing Selection Finches' beaks (Example)