Literature

Evolutionary theory is considered by many to provide integration and coherence to biology. 'Nothing makes sense without it', they say. Some have pointed to fish farming as an area where evolutionary thinking has practical applications and commercial relevance. This was the premise of a policy forum paper in November 2007 that addressed this topic:

"Darwinian evolution is the driving process of innovation and adaptation across the world's biota. Acting on top of natural selection, human-induced selection pressures can also cause rapid evolution. [. . .] studies based on fisheries data and controlled experiments have provided strong empirical evidence for fisheries-induced evolution over a range of species and regions. These evolutionary changes are unfolding on decadal time scales-much faster than previously thought."

Overfishing is a real problem in many parts of the world leading to rapid phenotypic changes.

Evolutionists have championed life-history theory, which "predicts that increased mortality generally favors evolution toward earlier sexual maturation at smaller size and elevated reproductive effort." The authors claim:

"Although alternative causal hypotheses can be difficult to rule out, fisheries-induced evolution consistently arises as the most parsimonious explanation after environmental factors have been accounted for. The question is not whether such evolution will occur, but how fast fishing practices bring about evolutionary changes and what the consequences will be.
Life-history traits are among the primary determinants of population dynamics, and their evolution has repercussions for stock biomass, demography, and economic yield."

The authors propose a tool for the management of evolving resources: Evolutionary Impact Assessment (EvoIA). Their enthusiasm for an evolutionary perspective is captured by the following quotes:

"An evolutionarily enlightened management approach is needed."
"This perspective emphasizes that evolution underlies ecology and influences economies."
"Successful management, therefore, will require the ecological and evolutionary consequences of fishing to be evaluated and mitigated. Adopting EvoIAs will enable fisheries managers to rise to this challenge."

It is worth distinguishing between the genetic changes occurring within contemporary ecosystems (often identified using the term microevolution) and the unobserved transformations that evolutionists need to explain the differences between organisms representing the higher taxonomic levels. The microevolutionary changes are not controversial, and those who would not identify themselves as Darwinians/evolutionary biologists are happy to work with life-history concepts in the context of ecological change.

However, two recent letters in Science have flagged up some additional interesting issues relating to the policy forum paper. Both challenged the view that fisheries-induced evolution (FIE) is the "most important driver of changes in life-history characteristics of heavily exploited marine fishes. Although Jorgensen et al. give the impression that this is well established, the evidence supporting FIE unfortunately remains circumstantial and is often open to alternative interpretations." The first letter questioned the evidence the authors provided to justify their proposed strategy:

"To make the case for EvoIAs, Jorgensen et al. present a selective set of studies - those concluding that FIE was a likely cause of the observed changes, after considering some environmental effects (see their table S2). In doing this, they excluded results that do not support their case. Furthermore, because FIE is often a matter of interpretation and the authors of the Policy Forum are strong advocates of FIE, the majority of the studies on life-history traits included in table S2 were their own. Their analysis does not represent a consensus opinion developed from critical scrutiny of the studies currently available."

The second letter made the point that observed changes do not equate with genetic changes. Consequently the EvolIA tool must be considered critically.

"This is a well-motivated idea in principle, but their reasoning relies entirely on the assumptions that fisheries-induced evolution (FIE) occurs commonly and that it is an undisputable fact. Neither of these assumptions is true. None of the studies of exploited fish populations in their article have provided genetic evidence for the observed phenotypic changes. Because evolution is by definition a change in the genetic constitution of a population, an evolutionary change cannot be postulated without demonstrating a genetic basis for the observed phenotypic shift. In fact, phenotypic changes in mean trait values due to simple environmental inductions are common, as are cases where populations are not evolving despite strong directional selection acting on heritable traits. Furthermore, several studies have shown that observed phenotypic shifts in exploited fish populations are fully consistent with simple environmentally induced changes."

More significantly, the second letter raises the important issue of Darwinians 'seeing the world' through coloured glasses. They acknowledge that some of the case studies listed in the Jorgensen et al. Policy Forum might genuine examples of FIE - but genetic confirmation is needed!

"However, until that proof is provided, the claims about FIE are nothing but "adaptive storytelling". As pointed out by S. J. Gould and R. C. Lewontin three decades ago, unwillingness to consider alternatives to adaptive stories, reliance on plausibility as a criterion for accepting speculative tales, and failure to consider adequately competing themes are characteristics of an "adaptationist program" that seems to have become revitalized in the context of fisheries-induced "evolution.""

Of course, Jorgensen et al. provided a response to these letters. What is of interest to this blog is the way Darwinism acts as a constraint on the thinking of scientists. They did not like being challenged on the lack of genetic evidence for FIE.

"This claim questions the fundamental assumption that scientists can make inferences about genotypes by studying phenotypes. It is worth remembering that Darwin formulated his theory of evolution with a similar assumption - that traits are heritable - nearly a century before DNA was found to carry hereditary information. Without such assumptions, evolutionary ecology could not operate."

It is worth remembering that Darwin thought all variations were evidence for his theory, allowing him to claim that natural selection was analogous to artificial selection. Mendel changed all that: most of the phenotypic variations we see are innate and they occur without any changes to the genotype.
There is no controversy that some Darwinian concepts are useful to ecology, but we must not allow the situation to develop where ecology is equated with Darwinism.

Correspondence: The Role of Fisheries-Induced Evolution
Howard I. Browman, Richard Law, C. Tara Marshall;
Anna Kuparinen, Juha Merila ;
Response by Christian Jorgensen et al.
Science 320, 4 April 2008: 47-50.

Managing Evolving Fish Stocks
Christian Jorgensen, Katja Enberg, Erin S. Dunlop, Robert Arlinghaus, David S. Boukal, Keith Brander, Bruno Ernande, Anna Gardmark, Fiona Johnston, Shuichi Matsumura, Heidi Pardoe, Kristina Raab, Alexandra Silva, Anssi Vainikka, Ulf Dieckmann, Mikko Heino, and Adriaan D. Rijnsdorp
Science 318, 23 November 2007: 1247-1248.

First paragraph: Darwinian evolution is the driving process of innovation and adaptation across the world's biota. Acting on top of natural selection, human-induced selection pressures can also cause rapid evolution. Sometimes such evolution has undesirable consequences, one example being the spreading resistance to antibiotics and pesticides, which causes suffering and billion-dollar losses annually (1). A comparable anthropogenic selection pressure originates from fishing, which has become the main source of mortality in many fish stocks, and may exceed natural mortality by more than 400% (2). This has, however, been largely ignored, even though studies based on fisheries data and controlled experiments have provided strong empirical evidence for fisheries-induced evolution over a range of species and regions (see table). These evolutionary changes are unfolding on decadal time scales-much faster than previously thought.