In a population of organisms, some are able to live so successfully that, when they die, they leave behind offspring to continue their role in the ecosystem. In any population, some individuals leave more offspring than others. It is the disproportionate reproductive success of individuals with certain traits, compared to others which lack those traits, which constitutes natural selection.
It was Darwin’s contention that the process of natural selection would gradually result, over long periods of time, in the acquisition of new body plans and the divergence of initially similar populations into groups which are quite different from each other and from the ancestor. Recent research however has demonstrated that these assumptions of Darwin are not correct.
The problem for Darwinism is that natural selection appears to be almost exclusively a process which results in loss of information. Thus, Michael Behe has pointed out: “Darwinian evolution is self-limiting – the same factors that make it work well on a small scale ensure that it doesn’t go far.” [Darwin Devolves p. 172] Dr. Behe also asserts: “It’s time to update the estimate of what natural selection can do – From the wonderful research on Darwin’s finches and other work …. Darwinian processes – cannot produce descendants that differ from their ancestor at the level of family or higher.” [p. 156 italics his] But there is more bad news for evolution theory: “The amazing but in retrospect unsurprising fact established by diligent work of many investigations in laboratory evolution over decades is that the great majority of even beneficial positively selected mutations damage an organism’s genetic information – either degrading or outright destroying functional coded elements.” [ p. 183 italics his][Michael Behe. 2019. Darwin Devolves. HarperOne]
A population may appear to have gained a wonderful new function, but closer examination reveals that the success comes at a cost. As Michael Behe declares “’damaging but beneficial’ mutations are the poison pills of Darwinian evolution. Plain old deleterious mutations aren’t nearly as bad, because negative selection can weed them out.” [p. 187] Sickle cell anemia represents such a poison pill type situation. Carriers in Africa survive malaria better when they have the sickle mutant, but this mutated condition nevertheless represents a serious loss of information on the ability to form normal red blood cells. Those people who inherit a copy of this mutation from each parent, are often seriously ill and may die.
The bottom line is that natural selection produces populations which are increasingly specialized for particular environments but which are less and less able to survive in a broader range of environments. This is not the direction an evolutionary process needs to go. It needs more new information, not less of some information previously present in the ancestral population.