I am proposing a thread to discuss the various meanings of complexity, information, and entropy, as they pertain to biology. I am bringing these three terms under the same title because they are often compared, equivocated, and confused with one another. Perhaps it would serve a useful purpose of clarification to debate the separate and connected meanings of these terms.
As a point of departure for this discussion I will use a description of the most compact of all the structures in the universe: the black hole. Stephen Hawking, in his
The Universe in a Nutshell (2001, p. 63), provides a relevant definition of the entropy of a black hole:
Not only does a black hole have a temperature, it also behaves as if it has a quantity called entropy. The entropy is a measure of the number of internal states (ways it could be configured on the inside) that the black hole could have without looking any different to an outside observer, who can only observe its mass, rotation, and charge.
Now, entropy has been famously likened to information, as well as to complexity.
Claude Shannon is the founder of
information theory. In addition to these formal definitions of entropy and information, there are equally formal definitions of complexity (for starters see
this from the Sante Fe Institute.)
So, I’ll venture an hypothesis (full of straw) that suggests this combined definition of entropy, information, and complexity applies to biology, specifically to genomics—the study of genomes. And, by paraphrasing Hawking, I’ll put forward this concept for measuring entropy, information, and complexity in a genome:
Not only does a [genome] have a temperature [?], it also behaves as if it has a quantity called [complexity]. The [complexity] is a measure of the number of internal states (ways it could be configured on the inside) that the [genome] could have without looking any different to an outside observer, who can only observe its [phenotypes, genotypes, and sex ratios]. (I'm dangerously speculating on the last insertion.)
As such, the numbers and combinations of alleles would make all the difference in a genome’s complexity. And by equating entropy, information, and complexity with way, I have ruled out the popular myth that humans are the most complex organisms on this planet. There are many genomes more complex than the one we own.
Do this help any? Or does it further confuse the application of entropy, information, and complexity to the biological sciences? What are your favorite definitions of these terms?
