Lewontin

Richard Lewontin, The Triple Helix: Gene, Organism, and Environment

 

Ch. 1 Gene and Organism

 

The price of metaphor is eternal vigilance. Indeed, the price of representation is eternal vigilance.

 

p. 5. Modern biology is framed in terms of genes and cell organelles. It is important to keep in mind here that the study of an organism's development has generated two disciplines: genetics and embryology. In her book Making Sense of Life, Evelyn Fox Keller argues that recent developments in embryology strongly counter the reductionist claim that geneticists made in the 1960s, "the organism can be deduced from its DNA." This is partly because of a wide variety of "feedback mechanisms" that control how the DNA is activated, and that control what goes on in the cell; and because of the importance of "positional information." (See picture.)

 

Preformationism, in its modern guise.

 

p. 9. Evolutionists want to explain the causes of variation, the differences among members of a species, and between closely related species. (Mutation + Selection of the 'fittest')

 

Developmental biologists want to describe the mechanisms common to all (or at least a wide range of) species. Lewontin says that means they are fixated on the genes; but Fox Keller insists that within developmental biology we must distinguish between the geneticists and the embryologists.

 

p. 11. For a geneticist, "the development of an individual is explained as the unfolding of a sequence of events already set by a genetic program."

 

p. 15. Lewontin argues that one dogma of genetic reductionists is "any variation observed among organisms must be the result of genetic differences." Or, p. 17. "if the development of an individual is the unfolding of a genetic program immanent in the fertilized egg, then variations in the outcome of development must be consequences of variations in that program." (Ex.: human diseases due to the mutation of clearly defined genes; drastic gene mutations in Drosophila that prevent the development of a wing. See p. 30: the norms of reaction of these mutations are not characteristic; the effects of many mutations of genes on the organism's phenotype are very sensitive to changes in environment.) 

 

We must also take into account the temporal sequence of external environments though which the organism passes its life. (See the account of the tropical vine; and the example of the achillea millefolium experiment. How can we "quantify" an environment? Why do we look for linear dependencies?)

 

And we must take into acccount the effect of random events of molecular interactions. P. 36. Developmental noise. Many biological processes take place in the midst of random processes, before they are stabilized.

 

Ch. 2. Organism and Environment.

 

Darwin: Adaptation is the process of becoming better fitted to the demands of the environment, and is the same process that leads to diversity: groups of organisms separated in time and space will evolve to fit different sets of circumstances as they find them.

 

p. 42. This set of assumptions divide the inside from the outside, the organism from the environment, which is then seen to be independent. The metaphor of lock and key. Organisms are then passive items, shaped by the environment (and, see Ch. 1, by their DNA).

 

pp. 44-45. Organisms solve problems posed by the environment.

 

p. 47. Having distinguished inner and outer, we need to reconsider their relations (without going back to holism). Organism and environment are causally interdependent.

 

No environment without an organism. (No pre-existing ecological niches.)

 

p. 51. Organism determine their niche, by its characteristic activities. The importance of microhabitats.

 

p. 54. Organisms actively construct their environment. Our envelop of air.

 

p. 54. Organisms alter their environment. Consumption and production. The creation of microclimates. The world is changing because the organisms are changing, as well as vice versa. The struggle between generations.

 

p. 60. Organisms integrate and differentiate. Squirrels and nuts. Cladocera detecting rate of change in external conditions, so that it switches from asexual to sexual reproduction. The transduction of signals.

 

p. 65. Different species live in different domains of physical forces. Global physical conditions are also the result of biological activity.

 

Ch. 3. Parts and Wholes, Causes and Effects

 

The machine model or simile was very useful for early modern science. But machines have clearly defined parts, with clear chains of causal connections among them. This leads to an oversimplified view of the relation of parts to wholes and of causes to effects in biology. It also leads scientists to "pose only those problems that are likely to be solved" by reductionist methods.

 

p. 73. Ex. The folding of proteins.

 

p. 74. The problem of mind.

 

The problem of shape. Positional information.

 

p. 75. Organisms are intermediate in size; they are internally heterogeneous; and they enter into complex relations with other heterogeneous systems. Thus!

 

p. 76. It is hard to know how to divide an organism up into organs, or functional units. You have to find the function, before you can trace it back to its causal "elements." And you have to guard against the error of "arbitrary aggregation."  Moreover, there are functions at different levels of aggregation.

 

p. 79. Indeed, there is, vertically, "a hierarchical cascade of functions that serve other functions above them; and there is also a horizontal multiplicity of functional pathways. Wholes in biology are determined by function; and parts can only be determined in relation to wholes.

 

p. 80: why the solar system is not like a human body. What is the Human Genome Project? Why is it problematic?  Why is it that "not every part serves a function"?

 

pp. 82-88. What is the meaing of the two tables? What is the meaning of the "fitness landscape"? What is so important about the configuration of lines 2, 3 and 4?

 

p. 88. "It is impossible to understand the situation of living organisms without taking into account their history." "Evolution is not an unfolding but an historically contingent wandering pathway through the space of possibilitites." Not every difference has an adaptive explanation. What is the point of the pictures on p. 90?

 

p. 92. Moreover, genetic variation depends on mutation. How rare are beneficial mutations?

 

"Living organisms... are the nexus of a very large number of weakly determining forces." (Another difference from the solar system, or a molecule, where there are a small number of interacting elements and forces, each of which has a major effect on the system when it is perturbed.

 

Note the great list on p. 93.

 

p. 94. Usually, normal variation along any of the multiple causal pathways doesn't have a strong effect on the organism, which tends to maintain its own stability (by homeostatic regulatory devices, and feedback devices, and the way it constructs its environment) in the face of normal perturbations. The problem with scientific method is that it lends itself to studying perturbations that create big changes; but this is abnormal, not normative, in the living world. P. 96: "the experimental organism that is perturbed strongly enough by a single causal deviation to show a reliable effect is an abnormal organism."

 

pp. 96-98. Why do "genes for wing size" or for autism or for intelligence appear to turn up in different locations?

 

p. 99. "The methodological limitations of experiments are confused with the correct explanations of the phenomena." "Only those phenomena are considered that lend themselves to the method."

 

p. 99-100. Difficulties about separating causes from effects. Feedback loops. Regulation. "Taken together, the relations of genes, organisms, and environments are reciprocal relations in which all three elements are both causes and effects."

 

p. The distinction between causes and agencies. An agency is a cause that always operates, although through different causal pathways, causes, no one of which is necessary or sufficient.

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