Darwin’s greatest achievement was not only to give a comprehensive view of the evolutionary process but also a plausible explanation of how it could have happened. He suggested that natural selection was the most important cause of evolution. However, he did not leave out the possibility that there might be other factors contributing to it. What is even more remarkable is that he suggested all of this without knowing anything about the processes of variation and heredity - Mendel only worked out the details later. Variation and heredity are two basic foundations of natural selection and explain perfectly some of the points Darwin had to make.
Darwin’s idea was radical. His theory suggests that evolution is just a natural process and according to one of his earliest critics, Robert Beverly MacKenzie, Darwin is implying that “In order to make a perfect and beautiful machine, it is not requisite to know how to make it.”
Darwin said that evolution by natural selection is an adaptive process or similarly adaptation is a mark of natural selection. Now, we know adaptation to be a quick process. According to Vidyanand Nanjundiah in "The Origin of Species after 150 years - one hundred and fifty years without Darwin are enough" (the phrase "One hundred years without Darwin are enough" was first proclaimed by the Nobel Laureate H. J. Muller in 1959):
“Crucially, natural selection works from one generation to the next: it deals with the short term. When one looks back over a great many generations, successive adaptations are seen to have accumulated and given rise to a major transformation, to what looks like a product of design .But the design is unintended, without purpose. There is no way in which evolution can plan for the future.”
This is because what trait is selected for depends on the organism’s environment. The environment not only includes its physical surroundings but also other individuals, species and populations it might be interacting with. Thus evolution is not an isolated process, it depends on selection pressures (the environment) and chance (Suppose if a certain proportion of the population moves to some new area. In this case only a limited gene pool which is isolated from the rest of the population will evolve separately. In another instance some natural disaster might cause only a certain portion of the population to survive, again limiting the gene pool. This is called genetic drift. Chance can also be explained by variation: many mutations that occur are neutral, that is, they neither confer an advantage nor disadvantage to the organism, so they must evolve independent of the environment). So, what we can conclude is that organisms and species are not necessarily evolving for the better. They are ‘just’ evolving, since evolution is a continuous process. Nanjundiah quotes the palaeontologist Van Valen:
“This implies that as a species evolves, it does not improve itself in any absolute sense. If it does not go extinct (which has been the fate of the vast majority of all species (yet another piece of evidence against betterment), the best it can do is to keep up with all the other species. He sums up the situation in the words of the Red Queen: “It takes all the running you can do, to keep in the same place" (Lewis Carroll, in Through the Looking Glass).”
Keeping all this in mind, now variation and heredity can explain how evolution can take place without foresight. Another of Darwin’s amazing ideas (without knowing the actual process) was that variation and heredity act independently of each other. Variations are the mutations that take place in an organism and they happen for a number of reasons. However, which chromosome goes to which gamete is completely independent of whether it contains a mutation or not. Again which gamete fertilizes with which one is also due to chance.
So what is the future of evolution? The agents of evolution (natural forces) are acting today as they have been acting since the beginning. However, there is a major change in the landscape of today: the appearance of humans. Human beings have become the foremost driving force of change on this planet, thus changing the environment and affecting evolution. The evolution of humans far exceeds that of any other animal, making us a dominant force. According to Nanjundiah:
“It is generally believed that along with the development of culture, natural selection has slowed down or become insignificant in humans. Instead, cultural evolution, which unlike biological evolution is largely Lamarckian, is said to have taken over.”
Lamarckian evolution is the idea that acquired characteristics can be transferred to the offspring. One of the most singular ability of humans is language, or at least the myriad complex ways of communication that have been established. The advances in science and knowledge have also given humans powers beyond any other life form on Earth. According to Daniel Dennet who is the Professor and Director of the Centre of Cognitive Studies at the Tufts University, Medford, Massachusetts, “Now, for the first time in its billion of years of history, our planet is protected by far-seeing sentinels, able to anticipate danger from the distant future – an asteroid on a collision course, or global warming – and devise schemes of doing something about it. The planet has finally grown its own nervous system: us. We are responsible for the future of life on the planet, in a way no other species could ever be.”
A most striking observation can be made from the above paragraph, not only have organisms and species been evolving over time, but Earth, as a planet has been evolving with them. With humans as its nervous system, it’s still a question whether we’re making way for the better or will just end up being an auto-immune disease?