Small Steps: What Constitutes a Small Step in Evolution?

Scientists say that evolution occurs in "small steps." But what exactly does that mean?

The first time I asked an evolutionist how an eye could evolve. He said, "It evolves in small steps." I kept pressing for the details of what these steps were, but he wouldn't give them to me.

Finally, I told him, "Listen, I feel like a guy who's asking you how to cross the Atlantic from New York to Paris. Your answer is that I cross the ocean in tiny steps. The problem is, if I simply take you at face value, I'm going to drown before I'm a hundred yards off shore. Please explain the steps!

Amazingly, he did.

I don't want to do injustice to his wonderful explanation by trying to mimic it. Instead, I'll let you read Charles Darwin's, contained in ch. 6 of On the Origin of Species.

Other "Small Steps"

If a fish were suddenly born with lungs and legs and began to walk on land, no one would believe that was a small step. But what if a fish were suddenly born with lungs and that was the only change? Could that be a small step?

It depends. My definition of a small step is something that is likely to happen in one generation.

The Evolution of the Lung

We actually know the steps that led to the lung. The evidence for it is very strong.

First some fish evolved the ability to use their swim bladder to collect oxygen. Skin or organs collecting oxygen from the air is not unusual, and the swim bladder is flotation device in fish containing air.

The swim bladder became more proficient at this, and then it evolved ridges and undulations inside, creating more surface area. Those ridges and undulations enlarged and connected, producing tubes, providing even more surface area.

The only step left was a tube to the outside so the fish could breathe the air in. That probably evolved before all the tubes developed in the former swim bladder. Many fishes have swim bladders open to the outside. Many don't.

You probably know that occasionally people are born with tails. We all know that people are born with extra fingers and extra limbs. Progressive evolution over thousands of years is obviously not needed for this to happen. It happens. We've seen it. (I'm sure you can find pictures on the internet.)

Whole body sections are regularly reproduced in species that already have those parts. It's no surprise that a human might be born with a third arm, though it might be a surprise if it were useful. It would be a huge surprise, however, if a dolphin was born with a human arm.

If mammals descended from fish somewhere in our prehistoric past, then it would be no surprise for a mammal to be born with gills. We used to have the genetic machinery for gills. However, science does not believe fish descended from mammals, so it would be a surprise for a fish to be born with lungs.

A fish obtaining lungs is not a small step. Lungs evolved in fish through much smaller steps.

A Growing Definition of a Small Step

Basically, small steps are adjustments to an individuals current physiology that can occur in one generation.

As our understanding of life grows, so does our understanding of what can change in a generation. We now know that there are genes that control whole sets of other genes. If that gene mutates into another form that the cell can read, then the individual's whole body form can be changed in a generation.

The likelihood of such a mutation being even workable, much less beneficial, is slim, but since mutations happen in every generation to every individual, at least in a few small ways, the likelihood can be exceedingly slim, yet still happen regularly.

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