In the talk.origins newsgroup James Coons raised the following question:
Sorry (in my own terminology), I would explain “inherent adaptation”as the “built-in” ability of an organism to adapt to its environment. For instance, I see parts of Natural Selection as being valid. I just don’t see that “new things” are created, nor do I see that “new material” or “new DNA” is created. Ultimately, my question is this, “Is every kind of adaptive change automatically attributed to Evolution, or is there a scientific “limit”? I hope you can understand this, because it is difficult to phrase.
This was my response:
This is a little difficult because it’s not clear to me what you know and don’t know. However lets review the bidding a bit.
An (metazoan) organism starts out life as a single cell. It has a master plan composed of DNA code. It develops into a mature organism. The features of this mature organism are a mixture of the innate and the environmentally impressed. (This is a major and somewhat misleading simplification but it will do.) In other words some ability to adapt to the environment is built into the organism.
These adaptations, e.g. calluses, are not heritable. Changes in the features of the organism due to adaptation during its life time do not propagate back into the genes. This type of adaptation is not evolutionary.
Now let’s take a for instance. Suppose we have a type of animal in a climate that is getting colder. Suppose we have two animals, let’s call them Fred and William. Both grow furry coats because it’s cold. Fred and William, however, have slightly different genes. Fred has to eat 900 daisies to get the wherewithal to grow his fur coat; WIlliam has to eat 1000 daisies to grow his. Times are hard and William doesn’t eat quite enough daisies. He freezes to death. Poor William. Let’s hold a moment of reverent silence for William.
You see what happens. In this herd (let’s call them mule-eared aardvarks) of animals, the next generation is sired by the Freds and not by the Williams. The next generation all get by on 900 daisies. There is an evolutionary adaptation because it is inherited.
I trust this is clear.
The moral of this little story is that the genomes (the DNA codes) of populations will shift around to track the changing environment. This is the basis for natural selection.
Now you ask, what are the limits to this. That is not such an easy question to answer. The problem is not with “new DNA” or changes in DNA. Mutations occur regularly; if you are statistically normal you have three mutations in your DNA. There are mechanisms for creating “new” DNA by duplicating genes.
One problem is that you don’t have a gene for trait X and a gene for trait Y and so and so forth. What you have are genes that code for proteins. The connection between genes and traits is indirect and convoluted. It is also rather sloppy. The upshot is that a change in a gene causes many small changes in the organism and, vice versa, many genes combine effects to produce a trait.
Another problem is that evolution cannot look forward to the future. Any change has to be viable in the current generation.
A third problem is that development (embryology) is a sequential process. A change in early development impacts everything that happens later on.
The upshot of all this is, yes, there are limits to the kinds of adaptations that can occur but it is very hard to say what they are. We can’t determine them explicitly. However we can do an end run.
Take, for example, the evolution of the eye. We can hypothesize a sequence of evolutionary changes leading from a photosensitive spot all the way up in complexity to the vertebrate eye. That’s all very well but can all of these intermediate stages exist. Are they all viable and feasible transitions. Here’s where we do the end run. We look around in nature and see that all of these intermediate stages do exist in different organisms. Hence we can be pretty sure that it was possible for eyes to evolve.
This page was last updated February 18,1998.