Center for the Philosophy of Biology

How shall we understand apparently teleological systems? What explains their persistence (returning to past trajectories following errors) and their plasticity (finding the same trajectory from different starting points)? Here I argue that all seemingly goal-directed systems-e.g., a food-seeking organism, human-made devices like thermostats and torpedoes, biological development, human goal seeking, and the evolutionary process itself-share a common organization. Specifically, they consist of an entity that moves within a larger containing structure, one that directs its behavior in a general way without precisely determining it. If so, then teleology lies within the domain of the theory of compositional hierarchies.

Insect societies -colonies of ants, bees, wasps and termites -vary enormously in their social complexity. Social complexity is a broadly used term that encompasses many individual and colony-level traits and characteristics such as colony size, polymorphism and foraging strategy. A number of earlier studies have considered the relationships among various correlates of social complexity in insect societies ; in this review, we build upon those studies by proposing additional correlates and show how all correlates can be integrated in a common explanatory framework. The various correlates are divided among four broad categories (sections). Under ' polyphenism ' we consider the differences among individuals, in particular focusing upon ' caste ' and specialization of individuals. This is followed by a section on ' totipotency ' in which we consider the autonomy and subjugation of individuals. Under this heading we consider various aspects such as intracolony conflict, worker reproductive potential and physiological or morphological restrictions which limit individuals ' capacities to perform a range of tasks or functions. A section entitled ' organization of work ' considers a variety of aspects, e.g. the ability to tackle group, team or partitioned tasks, foraging strategies and colony reliability and efficiency. A final section, ' communication and functional integration ', considers how individual activity is coordinated to produce an integrated and adaptive colony. Within each section we use illustrative examples drawn from the social insect literature (mostly from ants, for which there is the best data) to illustrate concepts or trends and make a number of predictions concerning how a particular trait is expected to correlate with other aspects of social complexity. Within each section we also expand the scope of the arguments to consider these relationships in a much broader sense of ' sociality ' by drawing parallels with other ' social ' entities such as multicellular individuals, which can be understood as ' societies ' of cells. The aim is to draw out any parallels and common causal relationships among the correlates. Two themes run through the study. The first is the role of colony size as an important factor affecting social complexity. The second is the complexity of individual workers in relation to the complexity of the colony. Consequently, this is an ideal opportunity to test a previously proposed hypothesis that ' individuals of highly social ant species are less complex than individuals from simple ant species ' in light of numerous social correlates. Our findings support this hypothesis. In summary, we conclude that, in general, complex societies are characterized by large colony size, worker polymorphism, strong behavioural specialization and loss of totipotency in its workers, low individual complexity, decentralized colony control and high system redundancy, low individual competence, a high degree of worker cooperation when tackling tasks, group foraging strategies, high tempo, multi-chambered tailor-made nests, high functional integration, relatively greater use of cues and modulatory signals to coordinate individuals and heterogeneous patterns of worker-worker interaction.

A hypothesis has been advanced recently predicting that, in evolution, as higher-level entities arise from associations of lower-level organisms, and as these entities acquire the ability to feed, reproduce, defend themselves, and so on, the lower-level organisms will tend to lose much of their internal complexity (McShea 2001a). In other words, in hierarchical transitions, there is a drain on numbers of part types at the lower level. One possible rationale is that the transfer of functional demands to the higher level renders many part types at the lower level useless, and thus their loss in evolution is favored by selection for economy. Here, a test is conducted at the cell level, comparing numbers of part types in free-living eukaryotic cells (protists) and the cells of metazoans and land plants. Differences are significant and consistent with the hypothesis, suggesting that tests at other hierarchical levels may be worthwhile.

SYNOPSIS. The maximum degree of hierarchical structure of organisms has risen over the history of life, notably in three transitions: the origin of the eukaryotic cell from symbiotic associations of prokaryotes; the emergence of the first multicellular individuals from clones of eukaryotic cells; and the origin of the first individuated colonies from associations of multicellular organisms. The trend is obvious in the fossil record, but documenting it using a high-resolution hierarchy scale reveals three puzzles: 1) the rate of origin of new levels accelerates, at least until the early Phanerozoic; 2) after that, the trend may slow or even stop; and 3) levels may sometimes arise out of order. The three puzzles and their implications are discussed; a possible explanation is offered for the first.

502 J . E V O L . B I O L . 1 4 ( 2 0 0 1 ) 5 0 2 ± 5 1 8 ã 2 0 0 1 B L A C K W E L L S C I E N C E L T D Minor transitions in evolution 503 J . E V O L . B I O L . 1 4 ( 2 0 0 1 ) 5 0 2 ± 5 1 8 ã 2 0 0 1 B L A C K W E L L S C I E N C E L T D Minor transitions in evolution 515 J . E V O L . B I O L . 1 4 ( 2 0 0 1 ) 5 0 2 ± 5 1 8 ã 2 0 0 1 B L A C K W E L L S C I E N C E L T D

The notion that complexity increases in evolution is widely accepted, but the best-known evidence is highly impressionistic. In this paper, I propose a scheme for understanding complexity which provides a conceptual basis for objective measurement. The Scheme also shows complexity to be a composite term covering four independent types. For each type, I describe some of the measures that have been devised and review the evidence for trends in the maximum and mean. In metazoans as a whole, there is good evidence only for an early-Phanerozoic trend, and only in one type of complexity. For each of the other types, some trends have been documented but only in a small number of metasoan subgroups. Key words. complexity, trends, hierarchy, Metazoa, macroevolution

SYNOPSIS. The maximum degree of hierarchical structure of organisms has risen over the history of life, notably in three transitions: the origin of the eukaryotic cell from symbiotic associations of prokaryotes; the emergence of the first multicellular individuals from clones of eukaryotic cells; and the origin of the first individuated colonies from associations of multicellular organisms. The trend is obvious in the fossil record, but documenting it using a high-resolution hierarchy scale reveals three puzzles: 1) the rate of origin of new levels accelerates, at least until the early Phanerozoic; 2) after that, the trend may slow or even stop; and 3) levels may sometimes arise out of order. The three puzzles and their implications are discussed; a possible explanation is offered for the first.

Insect societies -colonies of ants, bees, wasps and termites -vary enormously in their social complexity. Social complexity is a broadly used term that encompasses many individual and colony-level traits and characteristics such as colony size, polymorphism and foraging strategy. A number of earlier studies have considered the relationships among various correlates of social complexity in insect societies ; in this review, we build upon those studies by proposing additional correlates and show how all correlates can be integrated in a common explanatory framework. The various correlates are divided among four broad categories (sections). Under ' polyphenism ' we consider the differences among individuals, in particular focusing upon ' caste ' and specialization of individuals. This is followed by a section on ' totipotency ' in which we consider the autonomy and subjugation of individuals. Under this heading we consider various aspects such as intracolony conflict, worker reproductive potential and physiological or morphological restrictions which limit individuals ' capacities to perform a range of tasks or functions. A section entitled ' organization of work ' considers a variety of aspects, e.g. the ability to tackle group, team or partitioned tasks, foraging strategies and colony reliability and efficiency. A final section, ' communication and functional integration ', considers how individual activity is coordinated to produce an integrated and adaptive colony. Within each section we use illustrative examples drawn from the social insect literature (mostly from ants, for which there is the best data) to illustrate concepts or trends and make a number of predictions concerning how a particular trait is expected to correlate with other aspects of social complexity. Within each section we also expand the scope of the arguments to consider these relationships in a much broader sense of ' sociality ' by drawing parallels with other ' social ' entities such as multicellular individuals, which can be understood as ' societies ' of cells. The aim is to draw out any parallels and common causal relationships among the correlates. Two themes run through the study. The first is the role of colony size as an important factor affecting social complexity. The second is the complexity of individual workers in relation to the complexity of the colony. Consequently, this is an ideal opportunity to test a previously proposed hypothesis that ' individuals of highly social ant species are less complex than individuals from simple ant species ' in light of numerous social correlates. Our findings support this hypothesis. In summary, we conclude that, in general, complex societies are characterized by large colony size, worker polymorphism, strong behavioural specialization and loss of totipotency in its workers, low individual complexity, decentralized colony control and high system redundancy, low individual competence, a high degree of worker cooperation when tackling tasks, group foraging strategies, high tempo, multi-chambered tailor-made nests, high functional integration, relatively greater use of cues and modulatory signals to coordinate individuals and heterogeneous patterns of worker-worker interaction.

Evolutionary biology lost a unique, broad, creative, and influential thinker when Leigh Van Valen1 passed away on October 16, 2010 in Chicago at the age of 75. He was Professor Emeritus of Ecology and Evolution at the University of Chicago and served on the Committees on Evolutionary Biology, Conceptual Foundations of Science and Genetics. Unwritten ideas still coursed through his ceaselessly active mind as he fought and lost his last battle against phylogenetically distant and diverse microbes. We are a multiflavored ...

The Geozoic encompasses the 3.6 Ga interval in Earth history when life has existed. Over this time, life has diversified from exclusively tiny, single-celled organisms to include large, complex multicellular forms. Just how and why this diversification occurred has been a major area of interest for paleontologists and evolutionary biologists for centuries. Here, we compile data on organism size throughout the Geozoic fossil record for the three domains of life. We describe canonical trends in the evolution of body size, synthesize current understanding of the patterns and causal mechanisms at various hierarchical scales, and discuss the biological and geological consequences of variation in organismal size.

Historically, a great many features of organisms have been said to show a trend over the history of life, and many rationales for such trends have been proposed. Here I review eight candidates, eight "live hypotheses" that are inspiring research on largest-scale trends today: entropy, energy intensiveness, evolutionary versatility, developmental depth, structural depth, adaptedness, size, and complexity. For each, the review covers the principal arguments that have been advanced for why a trend is expected, as well as some of the empirical approaches that have been adopted. Also discussed are three conceptual matters arising in connection with trend studies: 1. Alternative bases for classifying trends: pattern versus dynamics; 2. alternative modes in which largest-scale trends have been studied: "exploratory" versus "skeptical"; and 3. evolutionary progress.

Little empirical work has been done to see what sort of patterns of change in morphological complexity ocrur in evolution, mainly because the complexity of whole organisms has been so hard to define and to measure. For serial structures within organisms, there are fewer difficulties; this paper introduces a set of complexity metrics that are designed especially for serial structures, and then explores some of the properties of the new metrics. Also, a principle proposed in the last century by Herbert Spenrer, and offered recently in a new form by the thermodynamic school of evolutionary thought, predicts that complexity should increase in evolution as a consequence of the accumulation of perturbations. Here, simulations in which perturbations are introduced to ideal and real series of vertebral measurements show how the complexity increase predicted by Spencer's principle would be captured by the new metrics.

The consensus among evolutionists seems to be (and has been for at least a century) that the morphological complexity of organisms increases in evolution, although almost no empirical evidence for such a trend exists. Most studies of complexity have been theoretical, and the few empirical studies have not, with the exception of certain recent ones, been especially rigorous; reviews are presented of both the theoretical and empirical literature. The paucity of evidence raises the question of what sustains the consensus, and a number of suggestions are offered, including the possibility that certain cultural and/or perceptual biases are at work. In addition, a shift in emphasis from theoretical to empirical inquiry is recommended for the study of complexity, and guidelines for future empirical studies are proposed.