I like to write about the wonder of science. But in the spirit of Johannes Kepler and his discoveries that went against his own fondest wishes, I’m writing today about an unpleasant aspect of the theory of evolution. It’s an important aspect, though, because ignoring it can lead to some profound misconceptions about the nature of the world in which we live.

Human beings are odd and unique creatures in that some members of our species are able to digest lactose as adults. All mammals, of course, digest lactose as infants, but as most mammals grow and develop that lactose-digesting enzyme, called lactase gets turned off. In certain human populations, particularly those of Europe and parts of Africa, the enzyme keeps functioning during adulthood.

One can think of this as a genetic adaptation that swept through the population. But what does that mean, really? Once a child is born, that child either has lactose tolerance or does not. What it means is that those without lactose tolerance, in general, did not reproduce. Why? Because they did not thrive. For many, perhaps most, it means that they died in childhood before they could have children of their own.

Think of what that meant for these children. They were born into a society that was becoming more and more dependent on milk and its products. Yet these children couldn’t digest these products. They got sick. They probably got weak from lack of nutrition. Many probably died.

The lucky ones, those with the gene for making lactase into adulthood, did thrive, did survive, did reproduce and pass that gene on into the next generation. That’s natural selection.

Natural selection is a wasteful process. It’s main tool is death – or at least inability to reproduce. But let’s face it. Lactose intolerance, and even malnutrition, don’t result in healthy, happy adults who just happen to be infertile. It results in dead people. Dead children.

So when we say something like, “Lactose tolerance swept through the population because it greatly aided survival,” what we’re really saying is that those with the gene lived, those without it died. And they died not just a death, but an unhappy and miserable death in which their bodies rejected the very sustenance offered them by otherwise loving and caring parents.

This is a harsh lesson, but an important one. Sometimes well-meaning people try to bridge the gap between science and religion, between evolution and God, by saying, “Evolution is how God did it.” Fine, you can believe that if you wish. There is certainly no test for or against that idea that I could think to devise. But be aware of what you’re saying when you make such a claim. Beware of the attributes you’re giving God.

I’m a parent of two amazing girls. I can’t imagine a more horrible event than losing either of them. Yet evolution depends on this event, counts on it. Death makes evolution go.

It’s not pleasant, but it is real. Science can reveal breathtaking wonder and beautiful, deep, unexpected connections. But we must always examine it openly, without bias, because it doesn’t have to conform to our wishes or hopes. And often, as Kepler found, it won’t.