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p.1 Our basic claim is that biological thinking about heredity and evolution is undergoing a revolutionary change... We will be suggesting that
- there is more to heredity than genes;
- some heredity variations are nonrandom in origin;
- some acquired information is inherited;
- evolutionary change can result from instruction as well as selection.
p.1 It is therefore quite wrong to think about heredity and evolution solely in terms of the genetic system. Epigenetic, behavioral, and symbolic inheritance also provide variation on which natural selection can act.
p.2 When all four inheritance systems and the interactions between them are taken into account, a very different view of Darwinian evolution emerges... When all types of hereditary variation are considered, it becomes clear that induced and acquired changes also play a role in evolution. By adopting a four-dimensional perspective, it is possible to construct a far richer and more sophisticated theory of evolution, where the gene is not the sole focus of natural selection.
p.5 The first dimension of heredity and evolution is the genetic dimension. It is the fundamental system of information transfer in the biological world, and is central to the evolution of life on earth.
p.62 As biologists have known for a long time, all multicellular organisms, including human beings, have a lot of developmental plasticity: their phenotype depends on a multitude of environmental factors, as well as their DNA.
p.77 The complex interactions between genes, and between genes and environments, mean that the effects of genes on the reproductive success of individuals are often nonadditive. What we know about development tells us that we should be thinking about networks, not single genes, as the unit of evolutionary variation.
p.77-78 When the network is your unit of evolutionary variation, then what you concentrate on is the evolution of the phenotypic trait that it affects. You focus on variation in traits, not genes, and follow the transmission of variations in traits. Moreover, when the unit of evolutionary change is a network of interactions, then the way the network is constructed, the constraints on its structure, its robustness and flexibility, become very important targets of selection. The processes leading to developmental plasticity (the capacity to adjust in response to conditions) and canalization (stability in the face of environmental or genetic perturbations) ...become of major importance in evolutionary change if you take this view. Plasticity and canalization are usually network properties, not properties of single genes.
p.109 The idea that DNA alone is responsible for all the hereditary differences between individuals is now so firmly fixed in people's minds that it is difficult to get rid of.
p.113 When liver cells divide their daughters are liver cells, and the daughters of kidney cells are kidney cells. Although their DNA sequences remain unchanged during development, cells nevertheless acquire information that they can pass to their progeny. This information is transmitted through what are known as epigenetic inheritance systems (EISs for short). It is these systems that provide the second dimension of heredity and evolution.
p.147 All the EISs transfer information from cell to cell, and that's their common denominator.
p.155 We are all sharp-eyed observers of behavior, and feel that our personal experiences qualify us to understand many of the complex processes that are related to behavioral change.
p.155-156 As far as we can, we want to deal with the third dimension of heredity and evolution, the behavioral dimension, in isolation from the first, genetic dimension.
p.161 we are going to distinguish just three major routes of behavior-affecting information transfer - three types of behavioral inheritance systems (BISs). The first is very similar to the transmission mechanism we described for Mongolian gerbils, since it is based on the transfer of behavior-influencing substances. The second is based on socially mediated learning in which individuals observe the conditions in which the behavior of experienced individuals is taking place, as well as the consequence of such behavior; although the inexperienced individuals do not imitate, they use what they observe to reconstruct a similar behavior. The third BIS involves imitation.
p.193 What is it that makes the human species so different and so special? What is it that makes it human? ...It is our ability to think and communicate through words and other types of symbols that makes us so different... Like Cassirer, we choose the use of symbols as a diagnostic trait of human beings, because rationality, linguistic ability, artistic ability, and religiosity are all facets of symbolic thought and communication.
p.193-194 This is what Cassirer wrote:
...this world [the human world] forms no exception to those biological rules which govern the life of all the other organisms. Yet in the human world we find a new characteristic which appears to be the distinctive mark of human life. The functional circle of man is not only quantitatively enlarged; it has also undergone a qualitative change. Man has, as it were, discovered a new method of adapting himself to his environment. Between the receptor system and the effector system, which are to be found in all animal species, we find in man a third link which we may describe as the symbolic system. This new acquisition transforms the whole of human life. As compared with the other animals man lives not merely in a broader reality; he lives, so to speak, in a new dimension of reality (Cassirer, 1944, p. 24; Cassirer's italics)
Cassirer goes on to suggest that rather than defining man as the "rational animal," we should define him as the "symbolic animal," because it was the symbolic system that opened the way to mankind's unique civilization.
p.194 What symbols are, how they form and develop, and how they are used are among the most complex issues in the study of man
p.200 in summary, we can say that signs - the pieces of information transferred from sender to receiver - become symbols by virtue of being a part of a system in which their meaning is dependent on both the relations they have to the way objects and actions in the world are experienced by humans, and the relations they have to other signs in the cultural system. A symbol cannot exist in isolation, because it is a part of a network of references.
p.201 All symbolic systems enable the construction of a shared imagined reality.
p.203 symbolic construction is not always concerned with present realities. It is often fictional and future-oriented... future goals, future scenarios, and future plans are part of the background against which newly generated information is edited.
p.204 symbolic systems are hierarchically organized... With symbolic systems we therefore have to think about the way that symbols can join to form ever-larger hierarchical structures, and about the ways in which the symbolic elements can be moved and reorganized to produce new meanings... The framework needed to interpret symbolic information has to be learned.
p.220 Human beings... construct the present in anticipation of what is to come.
p.221 Not only is the survival of an innovation dependent on the existing culture but so too are its generation and reconstruction, and all three are interdependent.
p.223 We have to recognize that the environment has a role in the generation and development of cultural traits and entities, as well as in their selection, and that new cultural variants are usually both constructed and targeted.
p.241 Through the symbolic system, we have the power of planing and foresight.
p.262 Notice that one of the corollaries of Waddington's canalization concept is that there is a lot of invisible genetic variation in natural populations. Canalization allows genetic changes to accumulate, because they are not "seen" by natural selection. They are revealed only if unusual environmental stresses or exceptional mutations push the processes of development well away from the normal canalized pathway. When this happens, new and selectable phenotypes may be produced. Paradoxically, therefore, while canalization masks genetic variation and prevents phenotype deviation in normal circumstances, the accumulation of hidden variation increases the potential for evolutionary change when internal or external conditions become dramatically different.
p.303 There is no reason to doubt that combining several different preexisting faculties can lead to important and surprising evolutionary novelties.
p.312 You can use the same line of reasoning to explain the evolution of increased plasticity as that which we used to explain canalization. The starting point is an environment that is changeable or constantly has new components introduced into it - new predators or new potential food sources, for example. Such environmental conditions will unmask variations in the capacity of individuals to make adjustments to changed conditions - variations that are not apparent in unchanging environments.... selection for increased flexibility involve[s]... the unmasking and selection of previously hidden variation.
p.356 of more general interest are the implications your version of Darwinism has for the dynamics of evolutionary change. It implies that evolution can be very rapid... there is also a good chance that such a change will be of adaptive significance, since it stems from already-evolved plasticity... evolved plasticity will bias the direction of evolution, simply because induced variations are nonrandom.
p.359 Simplification is fine, but it has to be of the right kind. It's no good if it misleads you or limits you too much.
p.377 Geneticists who take a developmental approach to evolutionary problems are traditionally interested in explaining two complementary aspects of development - canalization and plasticity. Canalization refers to the resistance of development to genetic and environmental variation: organisms can maintain a typical phenotype in spite of quite different genotypes and environments. Plasticity describes the way developing organisms can react to different conditions by producing a change in phenotype: the same genotype can produce several different phenotypes. Plasticity and canalization both show that genetic variation and phenotypic variation can be decoupled.
p.377 In her recent and important book Developmental Plasticity and Evolution, Mary Jane West-Eberhard has suggested that plasticity is one of the keys to understanding adaptive evolution... West-Eberhard's analysis shows how the evolved plasticity of development allows the evolution of new adaptive phenotypes without major genetic change, because variations can be self-perpetuating if the environmental inputs into development remain the same.
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