2. Adaptations Over Time
1.Evolution means change over time. In biology, the term eolution refers to changes in inherited characteristics in a species over time. That species evolve, or change over time, is a fact. It has been observed both in nature and in the laboratory. Several ideas have been proposed regarding just how this change takes place. The most widely accepted idea of how evolution occurs is the process of natural selection.
2. Resources, such as food, water, shelter and mates, are limited on Earth, This means that individuals must compete for resources. Natural selection states that the individuals best suited for their environments are better at competing for resources, which makes them more likely to thrive and produce more offspring
3. Adaptations make a species better suited for the environment. An adaptation is a variation in a trait that improves the chances of thriving and reproducing in a given environment. An inherited variation can be passed on to offspring. If it is, these offspring will be better adapted to the environment. They will thrive and produce more offspring than their competitors. further passing along the trait.
4. Let's look at how evolution might occur. Species A is a bird with a medium beak size that feeds on small and medium- sized seeds. Every generation, a few birds are born with slightly larger beaks. These birds can feed on slightly larger seeds than their medium-beaked relatives. The larger- beaked birds now have an advantage. They have access to a food with fewer competitors. With each generation, more birds that have inherited this larger-beak variation will be born into the population.
5. Over time, the larger-beaked birds may tend to associate more with each other than with the medium-beaked birds. They may begin mating only with other large beaked birds and producing offspring with large beaks when the large-beaked birds mate and reproduce only with each other and not with medium-beaked birds, they would be considered a new species species B Species B can no longer reproduce with Species A When two organisms can no longer produce offspring that can also reproduce, they are considered different species
6. While most scientists agree that natural selection is the way evolution occurs, there is some disagreement on how long it takes. Two major models have been developed to examine this issue. One model, called gradualism, proposes that changes in species result from slow changes over long time periods. According to gradualism, the example just given would occur very slowly over a long period of time--many. many generations, over hundreds or even thousands of years.
7. In contrast, the evolution model of punctuated equilibrium suggests that evolutionary change occurs in relatively short bursts followed by long periods of little to no evolutionary change. This model suggests that mutations in several genes would produce changes in one or several traits in a population. These changes would be so dramatic, however. that they would produce a new species within a fairly short time. It would happen within several generations. In the example, one or more mutations would lead to the sudden appearance of large beak size among individual birds in a population. This would produce a new species-Species B. Following this short period of rapid change, almost no major evolutionary changes would take place among this species for a very long period- perhaps thousands of years.