offspring that inherit the information (along with its carriers), and thereby expose inheritance system variants of a population to evolutionary processes such as natural selection and drift.

If these nongenetic adaptations, epigenetic, behavioral, or symbolic variants are to be considered true inheritance systems, part of organisms’ evolutionary legacies, they must contribute to fitness differences. Major challenges to extending investigations of nongenetic inheritance to an evolutionary context include development of new experimental tools and methods to distinguish genetic from nongenetic variation, methods of measuring fitness costs and benefits, and theory development to predict and explain evolutionary dynamics when more than one inheritance system is operating. Dual inheritance theories designed to handle cultural inheritance (e.g., Boyd and Richerson, 1985) only begin to scratch the surface of the types of inheritance systems and transmission rules involved.

CONCLUSION

Extending the concept of inheritance to include biotic and social relations implied by epigenetic mechanisms, social learning, symbolic communication through language, and interactions with environments raises questions about whether there might be a general theory of transgenerational “memory” for living systems. That is, is there a theory of biological conditions and mechanisms that record system states with the potential for closed information loops and an ontogeny and evolution of information? Just as growing awareness that genomes are dynamic complicates the simple concept that inheritance flows from genes to phenotypes and back to genes in the next generation, discoveries of other information loops (from behavior to environmental modification and back to behavior in niche construction and from symbols to social change and back to symbols in cultural evolution) present theoretical challenges as formidable as those faced by Mendel. What sorts of regular structures and mechanisms in behavior might there be to suggest transmission “rules”? What social mechanisms govern the production, manipulation, and propagation of symbols that can be captured in theories of cultural evolution? It took half of the 19th century to move from the most elementary understanding of the hereditary consequences of cross-breeding to Mendel’s theory and most of the 20th century to link the implications of Mendel’s theory to an understanding of the molecular mechanisms of the genetic system of inheritance in population and evolutionary processes. Scientists are only beginning to explore the mechanisms and theoretical implications of other inheritance systems and how these might interact in an expanded evolutionary dynamic.



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