In his book The Blind Watchmaker Richard Dawkins makes the claim that "biology is the study of complicated things which have the appearance of having been designed for a purpose." He goes on to argue, however, that the appearance is only illusory, a result of the blind tinkering of natural selection over eons of time. Maybe, but this has about it the sound of whistling past the graveyard.
As Michael Behe and others have noted, "If life gives the overpowering appearance of having been designed, then one is rationally justified in adhering to one's intuitions [that it is designed] unless and until a compelling reason is given to suggest that the appearance of design is only apparent."
So, is there a compelling reason to abandon one's belief that life is designed? Well, no. Some will argue, of course, that Darwin showed that design is a by-product of the purposeless process of evolution, but actually he did no such thing. What Darwin showed was that there are good reasons to think that evolution was the means by which living things diversify, he did not show that natural forces are ultimately responsible for the astonishing engineering and design that is ubiquitous in everything from living cells to the cosmos itself.
The argument of naturalists like Dawkins amounts to this: We know that the design in nature is only apparent because we know there is no intelligent designer. And we know there's no intelligent designer because there's no evidence that there one exists. And we know there's no evidence that an intelligent designer exists because the "overpowering appearance of purposeful design" that's cited as evidence is really only apparent. And we know it's only apparent because....Well, you get the picture.
The only way for the Darwinian naturalist to break out of this vicious cycle is to show that blind, purposeless forces can indeed create the appearance of complex purposeful design, but so far no one has been able to do this in a way that's convincing to anyone but those already committed to the belief that there is no intelligent designer.
If one is inclined to believe that an intelligent designer of the world exists there's no reason that any of the New Atheists have presented as to why that view should be given up. On the other hand, there are lots of examples in nature which confirm it. Maybe the simplest explanation for why nature has "the appearance of having been designed for a purpose" is because it has been.