Developmental Plasticity, Evolution and the Origins of Disease

Published on October 1, 2007 Reviewed on May 31, 2016   31 min

Other Talks in the Series: Evolution and Medicine

0:00
This lecture is about the connections between developmental plasticity, evolution, and the origins of disease. My name is Mary Jane West-Eberhard, and I work for the Smithsonian Tropical Research Institute in Panama, while living most of the time in Costa Rica. I confess that I am not a medical researcher. I am an evolutionary biologist. My research is primarily field work on the natural history and behavior of tropical social wasps.
0:24
Observations on these exquisitely conditioned sensitive organisms led first to an interest in the origin of workers and queens.
0:32
Which of these two forms, as developed by an individual female, is environmentally determined? From studying these, I got interested in developmental plasticity in general.
0:44
Developmental plasticity is simply the responsiveness of the phenotype to new inputs from the external or the internal environment. It's phenotypic change without genetic change.
0:56
The word phenotype, of course, refers to all traits of an organism other than its genes. This includes molecular products of genes, morphology, physiology, and behavior, including learned traits. It includes nervous tics, remembered phone numbers, and spots on the lung following a bout with the flu. That is, phenotypes can be adaptive or pathological, permanent or temporary, and typical or atypical of a species.
1:23
Developmental plasticity is a broader concept than phenotypic plasticity. Phenotypic plasticity is responsiveness to the external environment. Developmental plasticity includes responses to the internal environment. This means that includes sensitivity to things like gene products within cells and the action of hormones on tissues. Developmental plasticity includes modularity of structure.
1:48
Have you ever wondered how it can be that men and women with strikingly different faces can mate with each other, and yet all the different pieces somehow fit together in their offspring to make a coherent face? This is because the different pieces of the face are semi-independently developed, or modular, as shown in the side. And there is accommodation among adjacent bones other tissues. So modularity is a kind of internal plasticity during development. Since my main field of research is actually on the evolution of insect social behavior, I usually try to avoid extrapolating to humans. But I don't worry much about this in the case of developmental plasticity. Because it's a universal property of living things, almost a defining property of life.
2:35
No one would deny the developmental flexibility of human beings. You can see it beautifully illustrated and magazine covers everywhere and even in the California governor's office. A phenotype like this is affected by both the genes and environment or use, exercise. Most people realize the development is affected by both genes and environment. Yet genes never interact directly with the external environment. So how do genes and environment affect development really? The concept of developmental plasticity gives you an answer and I think a guide to thinking clearly about development. The plasticity or responsiveness of the developing phenotype is the key to understanding how normal and also abnormal development works. Every developmental event, healthy or pathological, starts with a pre-existing, developmentally plastic phenotype.
3:26
Then some new input, genetic or environmental, impinges on the plastic responsive phenotype and causes a developmental change. That is, I visualize developmental plasticity as responsible for both genetic and environmental effects on the phenotype. The naked genes can do nothing on their own. And a particular genetic effect depends as much on the nature of the pre-existing phenotype as it does on the specificity of the genetic or environmental input. If the preexisting phenotype is different, the same gene may elicit a different response. Or if the phenotype is not developmentally plastic in response to that particular gene product or environmental stimulus, there may be no developmental response at all. Specific events during development depend critically on the developmental plasticity of the organism, that is on particular abilities of the developing organism to respond to certain inputs at certain times.
4:22
Development has long been visualized like this, as a series of decision points and branching pathways of differentiation. The decision points are the nodes at the branching points. Those are the places where environmental conditions impinge on development to influence which path is taken and which genes are expressed in the developmentally plastic organism. It's important to appreciate the importance of internal environmental conditions for all developmental decisions. If gene expression were not environmentally sensitive, all genes would be either on or off at all times.
4:59
My favorite molecule to illustrate this is the hemoglobin molecule. I like it because of those four heme groups.
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Developmental Plasticity, Evolution and the Origins of Disease

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