Tag Archives: Biology

Word of the Day: Irreducible Complexity

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A novel about Christian apologetics and atheismMicrobiologist Michael Behe coined the term “irreducible complexity” to describe a system in which every part is mandatory. Here is his definition:

By irreducibly complex I mean a single system composed of several well-matched, interacting parts that contribute to the basic function, wherein the removal of any one of the parts causes the system to effectively cease functioning.1

Let’s look at a popular example, the remarkable bacterial flagellum. Built of several dozen different proteins, this tiny motor with a whip-like appendage can propel a bacterium 60 cell lengths per second. Compare this to the cheetah, the fastest land animal, which sprints at 25 body lengths per second. (Here’s a good agenda-less video showing the structure of the flagellum.)

The irreducible complexity claim is this: imagine turning the clock of evolution back. Which protein was the last to be put in place? Remove any protein from the flagellum and it doesn’t function. So if one step back in time from the working flagellum was something useless, no matter which protein you remove, why would evolution have created this thing? Evolution doesn’t spend effort slowly building elaborate nonfunctioning appendages on the remote chance that with a few more mutations over 100,000 generations it might get lucky and create something useful. But Intelligent Design comes to the rescue by postulating a Designer that put everything together all at once.

We can topple this thinking by considering an arch. Which was the last stone to be put in place in an arch? If you try to turn the clock back by removing the central keystone, the arch falls. So that one couldn’t have been last. But try removing any stone from the arch and the same thing happens. This makes the arch irreducibly complex, using this Intelligent Design thinking, with a Designer levitating the stones into place all at once as the only explanation.

But of course this is nonsense. If you imagine watching a movie of the building of an arch played backwards, the first change you’d see was not a stone removed but the last piece of scaffolding put into place. Then the remainder of the scaffolding to support the stones, then the stones removed one at a time, and then the scaffolding removed.

In the same way, the step that preceded the bacterial flagellum might have been the removal of an unnecessary piece of scaffolding.

There is much more to say about why the idea of irreducible complexity has not won over the science of biology, including attacks on how good an example the flagellum is of irreducible complexity, but that is a tangent for this post. For more on this topic, check out the links below.

Science may well have unanswered questions regarding the origin of the flagellum, but “I don’t know” is no reason to invent a Designer. And you can be sure that once the origin of the bacterial flagellum is sufficiently well understood, this argument will be discarded like a used tissue and some other complex feature of biology (and there’s always something) will be seized upon by the Intelligent Design advocate as the wooden stake that will finally destroy the monster that is evolution.

If the past is any indication, our ID friend will have a very long wait.

1 Michael J. Behe, Darwin’s Black Box (Touchstone, 1996), p. 39.

Photo credit: harrymoon

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A Defense of Abortion Rights: the Spectrum Argument

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Christianity and atheism debateA typical pro-life position can be stated this way: (1) human life begins at conception; (2) it is murder to take a human life; therefore (3) abortion is murder and should be considered immoral.

We’ll return to that idea shortly, but first let’s look more closely at human life. I argue that there is a spectrum of personhood during gestation.

Consider a continuous spectrum from blue to green. Where’s the dividing line? Where does blue end and green begin? We can argue about this, but we agree that blue is not green! The two ends are very different.

What age is the dividing line between child and adult? Twelve years? Eighteen? Twenty-one? It’s a spectrum, and there is no objectively correct line. Again, the line is debatable but no one doubts that a child and an adult are quite different.

An acorn is not a tree, a silkworm is not a dress, a water molecule is not a whirlpool, a piece of hay is not a haystack, and a carton of eggs is not a henhouse of chickens. Similarly, a single fertilized human egg cell is very different from a one-trillion-cell newborn baby.

Note that this is not simply about the number of cells. At one end of the personhood spectrum, we have arms and legs, fingers and fingernails, liver and pancreas, brain and nervous system, heart and circulatory system, stomach and digestive system—in fact, every body part that a healthy person has. And at the other, we have none of this. We have … a single cell. In between is a smooth progression over time, with individual components developing and maturing. That’s the spectrum we’re talking about.

Let’s approach this another way. Consider a brain with 100 billion neurons versus a single neuron. The single neuron doesn’t think 10–11 times as fast; it doesn’t think at all. The differentiation of the cells into different cell types and their interconnections in the newborn may count for even more than the enormous difference in the number of cells.

Note also that the difference between a newborn and an adult is trivial compared to the difference between the cell and the 1,000,000,000,000-cell newborn.

Some pro-life advocates argue that the humans at either end of this spectrum are identical in every meaningful way and use the term “baby” for every point along the spectrum. I’ve raised babies (with help, of course), and that makes me something of an expert in identifying babies. As an expert, I can assure you that an invisible cell isn’t a baby.

This inept attempt to collapse the spectrum by using the term “baby” for both ends is like the slogan used by the animal rights group PETA: “A rat is a pig is a dog is a boy.” In other words, there is no spectrum here: vermin are the same as livestock, which are the same as pets, which are the same as people.

No, a rat is not a boy, blue is not green, and a single cell is not a newborn baby.

A lot revolves around what we call this spectrum. Do we call it Homo sapiens? With this term, there is no spectrum, because the species is the same—the single cell is Homo sapiens, as is the newborn baby.

What about “human”? That seems a good name for the spectrum—that is, we would call the newborn human but not the cell. Or, we might call the cell human but not a human. Pro-lifers typically reject this, wanting to use “human” for both ends of the spectrum.

All right, can we all agree on “person”? I’ve heard pro-lifers reject this as well.

This game where pro-lifers deny names to the spectrum can get tiring. I really don’t care what the spectrum is called—humanity, personhood, human development, like-me-ness, whatever—call it what you want as long as the naming acknowledges the stark difference between the newborn (with arms and legs and a circulatory system and a nervous system and eyes and ears and so on) and the single fertilized human egg cell.

Now, back to the original pro-life argument: (1) human life begins at conception; (2) it is murder to take a human life; therefore (3) abortion is murder and should be considered immoral. This argument is invalid because it is oblivious to the spectrum.

Pro-lifers claim to be celebrating life, but equating a newborn baby with a single cell doesn’t celebrate life, it denigrates it.

Photo credit: Wikimedia

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