I finally finished Richard Dawkins' The Ancestor's Tale. I'd give it a B.
One bit I thought was especially interesting was a section where he commented negatively on what he calls "the tyranny of the discontinuous mind," a subject that he's also written about elsewhere. What he's talking about is people who are only able to think of things in discrete, black-and-white terms. The issue where the rubber most often hits the road is the concept of personhood. You can view the concept of personhood as an all-or-nothing affair, and determine the criteria by which something meets that definition (e.g. when an egg becomes fertilized by a sperm, that single cell is a person, and before that it's not). Or you can view personhood as a gradient (e.g. a 5 year-old is more of a person than a fetus, which is more of a person than a fertilized egg), with a sliding scale based on various criteria such as level of development, brain activity, etc.
I'd provisionally agree with Dawkins that discontinuous thinking, in the absence of continuous thinking, is a bane. But I'd make two points to qualify that.
One, discontinuous thinking is often desirable and necessary, especially when enacting laws. When is a person considered legally drunk? Currently, as far as I know, we have a threshold for blood alcohol levels. If you're beyond that you're considered legally inebriated; below it and you're not. We could enact a spectrum of various offenses depending on the exact blood alcohol level, but how fine do we slice it? Do we have 10 categories of inebriation? If we're doing any slicing at all, we're dividing a continuous variable into discrete chunks, so we really can't avoid it. And here's the thing...if you zoom in far enough, the continuous becomes the discontinuous, and if you pull far enough back, the reverse occurs, the discontinuous blurs into a continuum. The fact is, we simply cannot avoid legal categories if we want to have a system that's not bewilderingly complex to the point where it cannot function. So we have to define cut-off points.
This is what Roe v. Wade did with the abortion issue, by creating categories by trimester. Some abortion rights advocates would be in favor of advocating abortion at any time up until birth, while many pro-lifers want protection from abortion upon conception. They're both exhibiting discontinuous thinking, defining personhood in binary terms around a strictly-defined point in time: birth in one case, and conception in the other. Roe v. Wade affords incrementally more rights as the individual develops in the womb.
The last main point I'd want to make is that Dawkins is ignoring the reverse phenomenon, what I'd call the ineptitude of the continuous mind. It's important to be able to view the world from either perspective, as the situation calls for it. If you view everything as continuous, then you would essentially be unable to every make category distinctions or decisions. Many times we need to define hard boundaries and thresholds. Many times we need to sharpen distinctions between groups. In his own field of biology, Dawkins notes the slippery, continuous notion of many concepts, such as species and life. Populations may not always fall neatly into categories, but at the end of the day biologists must use category labels if they're going to be able to study, communicate, and attempt to make sense of it all. To apply purely continuous thinking would be to do away with boundary distinctions altogether, to say that life is just a spectrum of life forms that vary continuously along a spectrum. And that kind of fuzzy thinking is just as problematic as strictly discontinuous thought.
The obvious answer is that we need both, and we need to develop the judgment to determine in which cases each type of thinking most appropriately applies.