Sunday, March 21, 2010

Sex and Death: Evolution Undefined

Conceptually, evolution theory seems simple: 

Individual organisms vary in their various traits. Some are better adapted to survive in their environmental niche than others, because they possess (more and/or more highly) adaptive traits. Because the better adapted organisms succeed disproportionately in begetting offspring, the adaptive traits become more prevalent in the next generation. Over many generations, this process of filtering and concentrating the heritable traits of organisms has spawned diverse forms of life, with genes transferring traits from parents to offspring. 

I think I squeezed in all the relevant keywords.

This description works at an abstract level, but close up, the theory's fuzziness becomes apparent. What is a niche, anyway? Or an adaptation? Or a trait? Or an organism? Or a gene?

These questions make Kim Sterelny and Paul E. Griffiths’ Sex and Death a worthwhile read for anyone interested in probing the rigor of the received view. It turns out that researchers in the biological sciences have yet to settle on agreed-upon definitions of the above terms. Evolution theory is compromised by its own hazy vocabulary.

For example, do ecological niches exist independently of the organisms that fill them? Or are they defined by their occupants? Is average temperature sufficient to define a niche? Temperature and water salinity? Temperature, salinity, and the density of predators? “Niche” is, if not an essential, at least a supporting concept in evolution theory, but it amounts to a conceptual blur. Nobody can say what the necessary and sufficient conditions are to define a “niche.”

Organisms have many “traits.” But are they all “adaptations”? If so, why bother calling them “adaptations”—if it’s just another word for “trait”? If some traits are not adaptations, then what criteria can we use to distinguish those, presumably incidental, traits from adaptations? Nobody knows.

But then we have to ask, what counts as a trait? A compound eye? Or just the lens? Or the eye plus the optic nerve? That is, what’s nature’s granularity when it comes to carving up organisms into more and less adaptive “traits”? The theme of this “grain problem” runs throughout the book. At every turn, the authors use it to unsettle the received view.

While we’re at it, what counts as an organism? An ant? But a lone sterile worker has no capacity to beget offspring. Or, is the whole ant colony the organism (sometimes called a superorganism)? The authors underscore the “organism” problem with other examples from the invertebrates,

“Some colonial organisms also have bizarre life cycles. The Siphonophora—jellyfish-like colonial hydrozoans such as the Portuguese man-of-war—are so integrated that it is hard to say whether they consist of many cooperating organisms or a single organism. The various cells (the zooids) within the man-of-war are specialized: there are floatation specialists, propulsion specialists, killer cells, and sex cells. In this respect, the man-of-war seems to be a single organism. On the other hand, each cell within the colony has an independent origin in a fertilized egg. In contrast to the zooids that jointly form a man-of –war, cellular slime molds spend most of their life as independent cells. But when food runs out, they aggregate into a single body, which develops specialized parts. Some of the cells form a stem, ending in a group of cells that specialize in making spores. So these cells too seem to spend part of their life as individual organisms, and the rest as parts of an organism.”

And it’s not just invertebrates that pose the problem. Ninety percent of a human body’s cells are bacterial, not human. So, what constitutes the human “organism”?

“Gene” probably is the least salvageable term. In the early days of post-Crick-Watson genetics, a gene was taken to be a contiguous sequence of nucleotides that coded for a particular protein, the one-gene-one-protein model. But as scientists discover protein synthesis to be a remarkably complex process, that model has gone up in smoke. It’s not clear that anything discernible in a strand of DNA corresponds to “genes.” 

Log onto a news website, and watch the content load. The page you get is a mosaic of content pulled from news servers, ad servers, filters and recommenders of various kinds. The content served is the product of dynamic algorithmic operations. Nothing in the system of servers and databases corresponds to the static concept of “page,” and the same appears to be true when it comes to protein synthesis inside cells. Nothing in the system of DNA’s servers and databases corresponds to “gene.” In any case, DNA turns out not to be necessary for evolution, anyway

So the theory of evolution rests on a bed of semantic mush. The theory seems to boil down to saying merely that, if you wait long enough, life’s forms diversify. The lack of definition of its operative terms is a significant breach in the edifice of the theory, I think. 

Have the Intelligent Design advocates effectively exploited the breach? Misguided as the scriptural literalists among them are, the IDers perform a service by holding the scientists’ feet to the fire. So there you have it, IDers, Go sock it to ‘em! 

The subtitle of Sex and Death is “An introduction to philosophy of biology.” What a reasonable place to start. As is this.