Question

Compare and contrast Charles Darwin's and Alfred Russel Wallace's ideas/beliefs about natural selection (in depth).

Answer 1

• Darwin's idea about natural selection :-

Darwin's seminal book, On the Origin of Species, set forth his ideas about evolution and natural selection. These ideas were largely based on direct observations from Darwin's travels around the globe.

Over the course of his travels, Darwin began to see intriguing patterns in the distribution and features of organisms. We can see some of the most important patterns Darwin noticed in distribution of organisms by looking at his observations of the Galápagos Islands off the coast of Ecuador.

Darwin found that nearby islands in the Galápagos had similar but nonidentical species of finches living on them. Moreover, he noted that each finch species was well-suited for its environment and role. For instance, species that ate large seeds tended to have large, tough beaks, while those that ate insects had thin, sharp beaks. Finally, he observed that the finches (and other animals) found on the Galápagos Islands were similar to species on the nearby mainland of Ecuador, but different from those found elsewhere in the world.
Darwin didn't figure all of this out on his trip. In fact, he didn't even realize all the finches were related but distinct species until he showed his specimens to a skilled ornithologist (bird biologist) .Gradually, however, he came up with an idea that could explain the pattern of related but different finches.
According to Darwin's idea, this pattern would make sense if the Galápagos Islands had long ago been populated by birds from the neighboring mainland. On each island, the finches might have gradually adapted to local conditions (over many generations and long periods of time). This process could have led to the formation of one or more distinct species on each island.
During his voyage, and in the years after, Darwin developed and refined a set of ideas that could explain the patterns he had observed during his voyage. In his book, On the Origin of Species, Darwin outlined his two key ideas: evolution and natural selection.

Evolution :-

Darwin proposed that species can change over time, that new species come from pre-existing species, and that all species share a common ancestor. In this model, each species has its own unique set of heritable (genetic) differences from the common ancestor, which have accumulated gradually over very long time periods. Repeated branching events, in which new species split off from a common ancestor, produce a multi-level "tree" that links all living organisms.
Darwin referred to this process, in which groups of organisms change in their heritable traits over generations, as “descent with modification." Today, we call it evolution. Darwin's sketch above illustrates his idea, showing how one species can branch into two over time, and how this process can repeat multiple times in the "family tree" of a group of related species.

Natural selection :-

Importantly, Darwin didn't just propose that organisms evolved. If that had been the beginning and end of his theory, he wouldn't be in as many textbooks as he is today! Instead, Darwin also proposed a mechanism for evolution: natural selection. This mechanism was elegant and logical, and it explained how populations could evolve (undergo descent with modification) in such a way that they became better suited to their environments over time.
Darwin's concept of natural selection was based on several key observations:

1.Traits are often heritable. In living organisms, many characteristics are inherited, or passed from parent to offspring. (Darwin knew this was the case, even though he did not know that traits were inherited via genes.)

2.More offspring are produced than can survive. Organisms are capable of producing more offspring than their environments can support. Thus, there is competition for limited resources in each generation.

3.Offspring vary in their heritable traits. The offspring in any generation will be slightly different from one another in their traits (color, size, shape, etc.), and many of these features will be heritable.

Based on these simple observations, Darwin concluded the following:
1.In a population some individuals will have inherited traits that help them survive and reproduce (given the conditions of the environment, such as the predators and food sources present). The individuals with the helpful traits will leave more offspring in the next generation than their peers, since the traits make them more effective at surviving and reproducing.
2.Because the helpful traits are heritable, and because organisms with these traits leave more offspring, the traits will tend to become more common (present in a larger fraction of the population) in the next generation.
3.Over generations, the population will become adapted to its environment (as individuals with traits helpful in that environment have consistently greater reproductive success than their peers).
Darwin's model of evolution by natural selection allowed him to explain the patterns he had seen during his travels. For instance, if the Galápagos finch species shared a common ancestor, it made sense that they should broadly resemble one another (and mainland finches, who likely shared that common ancestor). If groups of finches had been isolated on separate islands for many generations, however, each group would have been exposed to a different environment in which different heritable traits might have been favored, such as different sizes and shapes of beaks for using different food sources. These factors could have led to the formation of distinct species on each island.

How natural selection can work :-

To make natural selection more concrete, let's consider a simplified, hypothetical example. In this example, a group of mice with heritable variation in fur color (black vs. tan) has just moved into a new area where the rocks are black. This environment features hawks, which like to eat mice and can see the tan ones more easily than the black ones against the black rock.
Because the hawks can see and catch the tan mice more easily, a relatively large fraction of the tan mice are eaten, while a much smaller fraction of the black mice are eaten. If we look at the ratio of black mice to tan mice in the surviving ("not-eaten") group, it will be higher than in the starting population.

Fur color is a heritable trait (one that can be passed from parent to child). So, the increased fraction of black mice in the surviving group means an increased fraction of black baby mice in the next generation. After several generations of selection, the population might be made up almost entirely of black mice. This change in the heritable features of the population is an example of evolution.

• Alfraid russel Wallace's idea about natural selection :-

Unlike Darwin, Wallace began his career as a travelling naturalist already believing in the transmutation of species. The concept had been advocated by Jean-Baptiste Lamarck, Geoffroy Saint-Hilaire, Erasmus Darwin, and Robert Grant, among others. It was widely discussed, but not generally accepted by leading naturalists, and was considered to have radical, even revolutionary connotations.

Prominent anatomists and geologists such as Georges Cuvier, Richard Owen, Adam Sedgwick, and Charles Lyell attacked it vigorously. It has been suggested that Wallace accepted the idea of the transmutation of species in part because he was always inclined to favour radical ideas in politics, religion and science, and because he was unusually open to marginal, even fringe, ideas in science.

Defence of Darwin and his ideas :-

After Wallace returned to England in 1862, he became one of the staunchest defenders of Darwin's On the Origin of Species. In one incident in 1863 that particularly pleased Darwin, Wallace published the short paper "Remarks on the Rev. S. Haughton's Paper on the Bee's Cell, And on the Origin of Species" to rebut a paper by a professor of geology at the University of Dublin that had sharply criticised Darwin's comments in the Origin on how hexagonal honey bee cells could have evolved through natural selection.

An even longer defence was a 1867 article in the Quarterly Journal of Science called "Creation by Law". It reviewed the book The Reign of Law by George Campbell, the 8th Duke of Argyll which aimed to refute natural selection.

Differences between Darwin's and Wallace's ideas on natural selection :-

Historians of science have noted that, while Darwin considered the ideas in Wallace's paper to be essentially the same as his own, there were differences. Darwin emphasised competition between individuals of the same species to survive and reproduce, whereas Wallace emphasised environmental pressures on varieties and species forcing them to become adapted to their local conditions, leading populations in different locations to diverge. Some historians, notably Peter J. Bowler, have suggested the possibility that in the paper he mailed to Darwin, Wallace did not discus selection of individual variations but group selection.However, Malcolm Kottler showed that Wallace was indeed discussing individual variations.

Others have noted that another difference was that Wallace appeared to have envisioned natural selection as a kind of feedback mechanism keeping species and varieties adapted to their environment (now called 'stabilizing", as opposed to 'directional' selection).

*If you have any doubt write in comment box and i will solve it and if you are satisfied plz rate my answer...