Biological evolution is not simply a matter of change over time. Lots of thingschange over time: trees lose their leaves, mountain ranges rise and erode, butthey aren't examples of biological evolution because they don't involve descentthrough genetic inheritance.
The central idea of biological evolution is that all life on Earth shares a commonancestor, just as you and your cousins share a common grandmother.
The notion of evolution is itself an idea that has emerged and evolvedover the past centuries. Thankfully, it is greater than any particulartheory about it can possibly encompass. There is every reason to hopethat the human mind, through careful engagement with the vast richnessand diversity of the living world and an ever-evolving will to see thingsmore deeply and adequately, will be able to break through present-dayconstrictions to ever grander views of this life.
As biologist Lynn Margulis, who is an iconoclast and not someone whosimply heeds conventional scientific wisdom, wrote in a critical editoriala couple of years ago in
Evolutionary biologists act certain that they know new life forms originate and complexify. But they don't.... Manybiologists claim they know for sure that (purposelesschance) is the source of inherited variation that generates new speciesof life and that life evolved in a single-common-trunk dichotomouslybranching-phylogenetic tree pattern. "No!" I say. Then how one species evolve into another? This profound research question isassiduously undermined by the hegemony who flaunt their "correct"solution.... Our zealous research, ever faithful to the god who dwellsin the details, openly challenges such dogmatic certainty. This isscience. (Margulis 2006, p. 194)
In the first sections of this essay I described a time in whichnaturalists did not "see" evolution. This changed. Today most people whostudy nature "see" evolution. Over time the Darwinian perspective becamedominant as an all-encompassing and powerful explanatory framework thatfits well with the modern propensity of mind to find general laws. Becauseit has become the dominant, established paradigm, we are in danger ofletting it constrict our view of life as the sole lens through which welook.
In the , which is over four hundredpages long, Darwin looks at a great variety of phenomena that he feelscan be explained in light of his theory of natural selection. It isfor him an exceedingly powerful and convincing framework in which tounderstand organisms and their history. There is, on Darwin's view,a kind of unwavering, unsentimental force of logic at work in nature andin evolution: "All that we can do, is to keep steadily in mind thateach organic being is striving to increase at a geometrical ratio; thateach at some period of its life, during some season of the year, duringeach generation or at intervals, has to struggle for life, and to suffergreat destruction" (1859/1979, p. 128). Amidst this destruction, "thevigorous, the healthy, and the happy survive and multiply" (ibid.). Theycarry the seeds of evolution into the future. For Darwin, as he says atthe end of the book, "there is grandeur in this view of life," because"from the war of nature, from famine and death, the most exalted objectwhich we are capable of conceiving, namely, the production of higheranimals, directly follows" (p. 459).
Scientific theories, however, must fit the evidence. Two examples of the evidence for Darwin’s theory of evolution — so widely used that I have called them “icons of evolution” — are Darwin’s finches and the four-winged fruit fly. Yet both of these, it seems to me, show that Darwin’s theory cannot account for all features of living things.
In Darwin does not touch on human evolution except toremark that "light will be thrown on the origin of man and his history"(p. 458). That light he brought to the public in his 1871 book, . There Darwin discusses human evolution and how humanity evolvedfrom monkey or ape-like ancestors.
During this time he nonetheless continued to carry out his studies onevolution and corresponded with numerous people about that work. He beganwriting in earnest in 1856 and had completed "two-thirds of the topicslater discussed in " by spring 1858 (van Wyhe 2007,p. 193). At this time a letter from Alfred Russell Wallace arrived,describing Wallace's own theory of evolution, which was remarkablysimilar to Darwin's - the idea was evidently "in the air." Darwincompleted in spring 1859, and it was published in thefall.
New features require new variations. In the modern version of Darwin’s theory, these come from DNA mutations. Most DNA mutations are harmful and are thus eliminated by natural selection. A few, however, are advantageous — such as mutations that increase antibiotic resistance in bacteria and pesticide resistance in plants and animals. Antibiotic and pesticide resistance are often cited as evidence that DNA mutations provide the raw materials for evolution, but they affect only chemical processes. Major evolutionary changes would require mutations that produce advantageous anatomical changes as well.
In the evolutionary process, an increase in biological complexity does not represent a “free lunch” — it is bought and paid for, because random genetic variation is subjected to natural selection by the environment, which itself is already structured. In fact, researchers are beginning to use Darwinian processes, implemented in computers or in vitro, to evolve complex systems and to provide solutions to design problems in ways that are beyond the power of mere intelligent agents.
But the extra wings are not new structures, only duplications of existing ones. Furthermore, the extra wings lack muscles and are therefore worse than useless. The four-winged fruit fly is severely handicapped — like a small plane with extra wings dangling from its tail. As is the case with all other anatomical mutations studied so far, those in the four-winged fruit fly cannot provide raw materials for evolution.
Back in England, first in London and then at his country homein Kent, Darwin pondered the causes of evolution. He continued to gatherevidence of evolution and began crafting his theory. In 1842 he wrotea first, thirty-five page sketch of his theory (in Darwin 2008). Hedid not share it with anyone, and it already contained many of the keyelements of what he published in . In the followingyears, Darwin had many other publishing commitments and undertook aswell an in-depth study of the biology and classification of barnacles.