Since we have been talking about proteins, let’s back up to say a few things about their building blocks – the amino acids. Below is a figure of an amino acid.

Note the central carbon atom and how it is covalently bonded with four different groups. Three of these four groups are always the same in every amino acid used by life: the amino group (orange box), the carboxyl group (blue box), and the hydrogen atom. The R signifies the side chain, which differs for each amino acid.

Life uses 20 different amino acids, as shown in the table below:

In essence, this is the palette of amino acids that are available to the blind watchmaker. The different amino acids are broken into different groups because of the chemical properties of the side chains. Those in orange are the hydrophobic (oily) amino acids. They will be found mostly inside the core of a globular protein as they are most useful in determining the basic shape of the protein surrounded by water. The others are hydrophilic and can be used to decorate the surface of the protein, allowing for specific interactions with other proteins and molecules inside the cell. The purple group is negatively charged, the blue is positively charged, and the green is uncharged.

Now I have previously argued that the blind watchmaker, like all designers, is limited by the building material that is available. So we need only ask ourselves a simple question – what if we cut down on the diversity of this palette? What if the blind watchmaker only had one member from each color-coded group to work with? What if the blind watchmaker had only the amino acids found in any particular color-coding (only hydrophobics or uncharged hydrophilics, for example)? What of the blind watchmaker only had three amino acids to work with? Say arginine, valine, and glycine? Or leucine, proline, and aspartate? Etc.

Could the blind watchmaker still produce a biosphere as diverse and resilient as that which exists with such scaled down palettes? I doubt this very much. After all, we could continue the thought experiments down to a single amino acid. Say that only glycine is available. If all proteins were simply chains of glycine, functional diversity would be gone, as they only thing that would differentiate the polypeptide chains is their length.

Those who would deny that the blind watchmaker is limited by its available building material would be in the absurd position of arguing a palette with one single amino acid would be just as useful as the current pool of 20 amino acids.

Of course, this raises an equally interesting consideration, namely, what if the palette contained many more amino acids, say 30 or 40? Would the blind watchmaker be any more successful? Would life contain adaptations and structures that have never been seen on this planet?

[Figures from aminoNOVA ]