Tuesday, February 07, 2006
The New Science of Eco-Devo
This paper discusses several ways in which the environment impacts the development of organisms. He points out that this area of research has been hampered by the fact that the specimens chosen for in-depth study were chosen precisely because they could grow reliably in a lab environment. Therefore, the sample of organisms used to study development are very irregular in the fact that their development doesn't count on environmental factors.
Some basic examples are:
- Some butterflies have different color phenotypes based on what season they were born in (dependent on day-length and temperature
- Snapping turtles are born male and female depending on the temperature
- Ant larva become workers/queens depending on diet
- Some toads can develop alternate phenotypes depending on whether or not the pond is drying up
- Orthodontic problems in humans may be caused by overly-soft diets in children (it is the increased chewing and tension in the jaw that stimulates the bone and muscle growth
The paper focused on predator-induced polyphenisms. Specifically, kairomones, which are soluble chemicals released by animals (kind of like aqueous pheromones). Basically, a prey, during its development, can detect the fact that it is sharing the water with a predator, and have an adaptive change induced.
- If you raise Daphnia in water in which Chaoborus was previously cultured, it will induce a neck spine or helmet.
- If the carp Carassius carassius is developing in the water with a pike that has already eaten a carp, it will have induced a morphology that will not fit into the pike's jaws.
- Gilbert pointed to the human immune system as a giant example of a predator-induced polyphenic system (antibodies produced by our mothers give us passive immunity when we are born).
What's even more interesting (especially to creationists) is the concept of genetic assimilation. If a phenotype is induced environmentally for enough generations, the inducer can internalize such that future progeny will have the phenotype even in the absence of the inducer. Examining the mechanisms behind this would be an excellent project for a baraminologist (there are some papers referenced, but I have not read them and do not know how well they cover the subject).
On an ecological consideration, Gilbert points out that the lack of research in this area may mean that some of the chemicals we introduce into the environment may cause developmental problems in organisms. This is something that is not normally considered to the extent that it should.
I thought that the most interesting parts were (a) that organisms during development can sense the animals in their ecology and respond appropriately, and (b) these changes can be converted into internally-generated, thus giving another mechanism for baraminic diversification.
Lots of good things to think about. In fact, the paper covers lots of things I just didn't have time to mention. This is a must-read.
Although this may have hampered eco-devo its precisely whats needed to avoid confusion. Manipulate one variable at a time. The environment is controlled, the organism is controlled. If it was not variances could not be blocked and dependencies to the independent variable would not be able to be established.
2. "very irregular in the fact that their development doesn't count on environmental factors." This is not an irregularity. The environmental conditions in the lab are purposefully kept constant for the reasons stated in #1. In ecological systems the environmental conditions are by definition uncontrolled hence variations in populations are observed. Laboratory conditions ARE controlled hence phenotypic variations are not observed as regularly.
In fact, laboratory strains of animals often cannot thrive in nature BECAUSE they have been in the lab so long they have evoloved to the precise laboratory conditions. Natural selection has streamlined the lab organisms. When released into the wild they no londer have the phenotypic plasticity required to compete with wildtype organisms.
3. The paper you cite does not not challenge present evolutionary theory in any way. All these aspects can be predicted and observed by evolutionary theory.
I don't disagree. The issue, however, is that we may have over-generalized our understanding because we are using organisms that are not representative of organisms in general, and are instead representative of the environments in which we can study them. This needs to be taken into account when applying the results of other organisms to the world as a whole.
"This is not an irregularity."
See Gilbert's comments below. He seems to think it is.
"The environmental conditions in the lab are purposefully kept constant"
This has nothing to do with whether or not organisms amenable to these conditions are regular or irregular.
"Laboratory conditions ARE controlled hence phenotypic variations are not observed as regularly"
I think you need to read the article. Here is an extended quote:
Each of our model systems for developmental biology...has been selected for small body size, large litter size, rapid embryonic development, early sexual maturation, the immediate separation of the germ-line from somatic lines, and the ability to develop within the laboratory. These last two criteria are very important because they eliminate the effects of the environment on development...The shortcoming of our model systems is that they do not represent development in the real world. Most organisms probably will not develop well in the laboratory. There are environmental cues that regulate and permit development to occur. [emphasis mine]
The point he is making is not that the model systems become adapted to the lab environment, but rather they were chosen because other types of organisms do not survive there. So it may be problematic to generalize organisms that do not take lots of environmental cues for development (and thus can survive in a lab) to those that do.
Note also that in microorganisms for example, there are large numbers of microorganisms that we don't know much about (or perhaps nothing at all) because they can't be cultured. In fact, most bacteria species cannot be cultured, and therefore cannot be studied by normal methods.
Therefore, we need to keep in mind when generalizing statements about microorganisms that we know very little about microorganisms that we cannot culture, and thus may not be able to generalize to them as much as we'd like.
"The paper you cite does not not challenge present evolutionary theory in any way. All these aspects can be predicted and observed by evolutionary theory."
So what? Whether or not it challenges or does not challenge "evolutionary theory" (as if that were a monolithic, singly-conceived idea) is irrelevant to its relevance to Creation biologists.