This is the second in a series of three papers devoted to energy flow and entropy changes in chemical and biological processes, and to their relations to the thermodynamics of computation. In the first paper of the series, it was shown that a general-form dimensional argument from the second law of thermodynamics captures a number of scaling relations governing growth and development across many domains of life. It was also argued that models of physiology based on reversible transformations provide sensible approximations within which the second-law scaling is realized. This paper provides a formal basis for decomposing general cyclic, fixed-temperature chemical reactions, in terms of the chemical equivalent of Carnot's cycle for heat engines. It is shown that the second law relates the minimal chemical work required to perform a cycle to the Kullback–Leibler divergence produced in its chemical output ensemble from that of a Gibbs equilibrium. Reversible models of physiology are used to create reversible models of natural selection, which relate metabolic energy requirements to information gain under optimal conditions. When dissipation is added to models of selection, the second-law constraint is generalized to a relation between metabolic work and the combined energies of growth and maintenance.
This is the first of three papers analyzing the representation of information in the biosphere, and the energetic constraints limiting the imposition or maintenance of that information. Biological information is inherently a chemical property, but is equally an aspect of control flow and a result of processes equivalent to computation. The current paper develops the constraints on a theory of biological information capable of incorporating these three characterizations and their quantitative consequences. The paper illustrates the need for a theory linking energy and information by considering the problem of existence and reslience of the biosphere, and presents empirical evidence from growth and development at the organismal level suggesting that the theory developed will capture relevant constraints on real systems. The main result of the paper is that the limits on the minimal energetic cost of information flow will be tractable and universal whereas the assembly of more literal process models into a system-level description often is not. The second paper in the series then goes on to construct reversible models of energy and information flow in chemistry which achieve the idealized limits, and the third paper relates these to fundamental operations of computation.
The most significant legacy of philosophical skepticism is the realization that our concepts, beliefs and theories are social constructs. This belief has led to epistemological relativism, or the thesis that since there is no ultimate truth about the world, theory preferences are only a matter of opinion. In this book, William Harms seeks to develop the conceptual foundations and tools for a science of knowledge through the application of evolutionary theory, thus allowing us to acknowledge the legacy of skepticism while denying its relativistic offspring.
This highly interdisciplinary book discusses the phenomenon of life, including its origin and evolution (and also human cultural evolution), against the background of thermodynamics, statistical mechanics, and information theory. Among the central themes is the seeming contradiction between the second law of thermodynamics and the high degree of order and complexity produced by living systems. This paradox has its resolution in the information content of the Gibbs free energy that enters the biosphere from outside sources, as the author shows. The role of information in human cultural evolution is another focus of the book. One of the final chapters discusses the merging of information technology and biotechnology into a new discipline — bio-information technology.
A new study by Noam Sobel, of the Olfaction Research Group at the Weizmann Institute of Science in Rehovot, Israel, and others are reporting in the journal Science this week that men in their study who sniffed the tears of crying women produced less testosterone and found female faces less arousing.
Previous studies in animals such as mice and mole rats have shown that tears convey important chemical messages which are used to attract or repel others of the same species. There is good evidence for an interesting type means of higher-level chemical communication. These previous studies also incidentally show that “emotional” tears are chemically distinct from “eye-protecting” types of tears.
Scientific American’s “60 Second Science” (via link or listen below) podcast has a good audio overview of the study for those without the time to read the paper.
In press reports, Adam Anderson, a University of Toronto psychologist who was not involved with the study, posited that the results may imply that “tears have some influence on sexual selection, and that’s not something we associate with sadness.” He continued, “It could be a way of warding off unwanted advances.”
This study provides a new hypothesis for the evolution of crying in humans. (Now if only we could find some better reasons for laughter…)
The take home message may be that guys should not take their dates out to weepy chick flicks, or alternately women reluctantly accepting “pity dates” should force their suitors to exactly these types of testosterone damping films.
From hiccups to wisdom teeth, our own bodies are worse off than most because of the differences between the wilderness in which we evolved and the modern world in which we live.
Constitutional debate continues over whether public schools should include biblical Armageddon alongside global warming in end-of-world curriculum.