Evolutionary theory suggests that life evolved in a series of small steps spread out over a very long period of time. Take the eye as an example. The human eye is extraordinarily complex. How did we get it? Evolutionary theory points to other animals with less complex eyes, such as jellyfish which have just a few light sensitive cells or starfish which has a more sophisticated eye than the jellyfish, but still only a very crude type of lens. The argument then runs that over time the eye developed gradually, from simple light sensitive cells through to the marvel of the human eye.
In 1996 molecular biologist Michael Behe published a book which challenges this concept. Behe has no problem with the thought that the universe is billions of years old or that life branched out from a common ancestor. The problem he points out is that molecular biology shows us that even the crude eye of the jellyfish is not simple. When Darwin formed his theory and when Neo-Darwinism developed it, molecular biology didn’t exist. We had no idea what goes on at the most basic level of existence – that is inside the cell. Now we do, and according to Behe what we’ve discovered are amazingly complex and elaborate chemical processes.
Behe suggests that these processes are “irreducibly complex”. Think of a mousetrap. It has a number of parts – a wooden base, a U-shaped metal hammer which crushes the mouse, a spring to activate the hammer, a holding bar to hold the hammer down, and a sensitive catch which releases the bar at the time a mouse nibbles the cheese. Take away any of these parts and the mousetrap won’t work. You won’t have a less crude instrument for catching mice if you take away the spring. You won’t have a less crude instrument if you replace the base with a paper one. It simply won’t work. There is no way to have a step by step development that yields a mousetrap.
Behe suggests this is what it’s like at the level of the cell, the basic building block of life. Its processes are not only complex, but irreducibly complex. There is no way to explain the emergence of the cell using the idea of gradual development from the simple to the more complex. And as the cell is the basic building block of life this suggests that although Darwinian evolution may be able to explain the development of life once the cell has emerged, it is unable to explain how the cell came to exist in the first place.
Source: Scott Higgins summarising from Michael J Behe, Darwin’s Black Box (Touchstone, 1996)