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A Leaky Faucet: Why Darwinian Evolution Leads to Loss of Information


In 2010 biochemist Michael Behe published a paper in the Quarterly Review of Biology in which he concisely stated the first rule of adaptive evolution: "Break or blunt any functional coded element whose loss would yield a net fitness gain." By this he meant several things. First, there are indeed adaptive mutations -- that is, mutations that yield a benefit to the cell under a particular set of circumstances. Second, the primary way such adaptation occurs is by breaking or inactivating some non-essential pre-existing function, in order to make the cell more fit, more competitive than its neighbors.

Behe was talking about microbes -- viruses and bacteria -- but his rule also applies at the cellular level in higher organisms. The best example where this rule is played out is in cancer. Cancers develop when one or more normal functions in a cell are disrupted or broken. The ironic thing is that for the cancer cells, this breaking increases their fitness, their rate of growth and cell division, and thus is beneficial -- to them. Normal constraints have been removed, allowing uncontrolled growth. For the cancer cell that's good, but bad for us, of course. So one can say that cancer is a prime example of what adaptive evolution can accomplish on the multicellular level, by breaking or disrupting some normal function.

What does Behe's first rule of adaptive evolution say about evolution in general? If most "beneficial" mutations are due to the loss of something rather than a gain of something, we are losing information when most adaptations occur, sometimes irreversibly. Let me give an example.

Microbiologist Ralph Seelke and I published a paper in 2010 where we demonstrated that cells always, or nearly always, take the easiest road to success. Given a choice between a simple two-step path leading to repair of two genes needed to make tryptophan, versus a one-step path that eliminated expression of the those genes, only one out of a trillion cells went down the path toward making tryptophan, even though that path would ultimately be much more beneficial. Why did this happen?

The genes to be repaired were overexpressed -- too much of their products were made. Because one of the genes was broken in two places, no tryptophan could be made. Thus both genes were expensive to keep around. It was easier for the cell to break the useless genes than to repair them -- one step instead of two -- and the cells, having no foresight, took that path. Some of those cells deleted the genes, thus losing the information needed to make tryptophan for good.

Let me explain in everyday terms. A faucet leaking badly but with no way to hook it up to a hose is entirely useless. While it is relatively easy to repair the faucet, requiring only two parts, the owner of the faucet doesn't know that. Since he can do without the faucet, he is likely to cap it to stop the expense of the wasted water. But he has lost the ability to water his backyard using that faucet.

Like the clueless homeowner, evolution has no foresight and does not know there is a big payoff just two mutations away. If the cells can prevent the overexpression of the tryptophan genes or remove them in a single step, that's what they will do, especially since there are many more ways to inactivate a gene than to repair it. Any cell that does this instantly becomes more fit than its neighbors, because it is spending less energy making useless stuff.

In fact, that is what we observed. Nearly all the cells inactivated the genes (only one out of a trillion didn't). Some of the cells even deleted the genes, thus losing the capacity to make tryptophan for good. Darwinian evolution travels by the shortest road, without regard for where it's headed. And if the shortest road is to break an existing function -- to lose information -- that's the path it chooses.

I'm sure you can think of parallels in the business world, when only the bottom line, corporate fitness, is what matters, and executives have no long-term vision. They don't see how some things, if adjusted, may yield big payoffs. As a result, whole technologies can be decimated or lost in a push for efficiency, technologies that if maintained could prove vital in the future. But fortunately, unlike Darwinian evolution, we do have foresight and can plan ahead. We do have the capacity for innovation, and can make wise choices or correct our mistakes.

The process of innovation is the opposite of the first rule of adaptive evolution. In the biological world, the quickest road to adaptation may be to delete or inactivate genes that are not necessary. But you don't get new features by deleting information. Building something new, which is what is required to explain the diversity around us, requires more than the happenstance and selection of Darwinian evolution. It requires foresight, planning, and a clear picture of the goal. It requires intelligent design.

Image credit: Forest & Kim Starr [CC BY 3.0], via Wikimedia Commons.