Explain how limbless salmanders evolved according to Darwin's theory of natural selection?
http://salamander.uky.edu/srvoss/Nov23.pdf
To answer your question, you have to understand a couple of things. First, limbless salamanders are descended from limbed salamanders. In other words, limblessness isn't a primitive, but rather a derived trait for salamanders. Limbs have been lost secondarily. Secondly, you'll want to look up information on limbless salamaders (Google it, or use the library: there are lots of good books about salamanders.) There you will find infomation on the autoecology or lifestyle of these salamanders. Where do they live? How do they get around? Most importantly, what advantage might they have in their environment by NOT having limbs? Natural selection operates on populations of organisms; populations are subject to different environmental pressures (selective pressures). Forexample, animals living in caves are often blind (their ancestors could see), but have lost that ability through selection, because mutations that rendered an animal blind were not a disadvantage, and might actually be advantageous. By the way the article cited above is about neoteny, which is a fascinating case where some salamanders retain their larval characteristics yet are able to breed (imagine a giant baby that could have its own children). It doesn't address your question, though.
According to Darwin's theory of natural selection, the evolution of limbless salamanders can be understood by considering the principles of variation, heritability, and fitness.
Firstly, in a population of salamanders, there is inherent variation in traits such as limb length and structure. This variation arises due to random genetic mutations, recombination, and other factors. Some salamanders will have longer limbs, while others may have shorter or even no limbs at all.
Secondly, these variations are heritable. Offspring inherit genetic traits from their parents, including the traits related to limb development. So, if a salamander with shorter limbs reproduces, there is a chance that its offspring will also have shorter limbs.
Now, let's consider the concept of fitness. In nature, individuals with traits that increase their chances of survival and reproduction have higher fitness. Fitness is not solely determined by physical attributes but also the ability to adapt to their environment.
In the case of salamanders, consider an environment where long limbs are more advantageous. These long-limbed salamanders might be better at climbing trees, capturing prey, or avoiding predators. As a result, they are more likely to survive, reproduce, and pass on their long-limbed traits to their offspring.
However, in certain environments, having no limbs or shorter limbs could be advantageous. For example, limbless salamanders may be more efficient at burrowing through soil or escaping predators in tight spaces. In such situations, these limbless variations may have higher fitness and better chances of survival and reproduction compared to their long-limbed counterparts.
Over time, as these limbless salamanders with higher fitness mate and produce offspring, the frequency of limbless traits in the population will increase. This process is known as natural selection, where advantageous traits become more common in a population over generations.
It is important to note that evolution is a gradual and continuous process, taking place over thousands or millions of years. The evolution of limbless salamanders would require multiple factors like genetic variation, heritability, and fitness working together through natural selection to produce the observed outcome.