In his classic study,The Great Chain of Being, Arthur Lovejoy delineated a complex set of concepts and assumptions which referred to the perfection of God and the fullness of creation. In attempting to distil the basic or ‘unit idea’ which constituted this pattern of thought, he focused on the assumption that ‘the universe is aplenum formarumin which the range of conceivable diversity ofkindsof living things is exhaustively exemplified’. He called this the ‘principle of plenitude’. Lovejoy argued that this idea implied (...) two others—continuity and gradation—and that together these reflected a pre-occupation with the ‘necessity of imperfection in all its possible degrees’, a concern which had pervaded Western thought since Plato and gave rise to the powerful ontology known as the ‘great chain of being’. (shrink)

There are few more likeable figures in the history of science than Alfred Russel Wallace. A warm-hearted and generous man, he won the admiration of virtually all who knew him for what one contemporary called ‘the charm of his personality’. Typical of this charm was his behaviour over the potentially sensitive question of his co-authorship with Darwin of the theory of natural selection. Ignoring all the disputes which might so easily have followed the events of 1858, Wallace never ceased to (...) give Darwin all the credit for their theory. In 1864, the author of theOriginchided the younger man for his deference, writing, ‘you ought not … to speak of the theory as mine; it is just as much yours as mine. One correspondent has already noticed to me your “high-minded” conduct on this head’. But Wallace's reply was equally firm, ‘As to the theory of Natural Selection itself, I shall always maintain it to be actually yours and yours only’. If anyone is responsible for the comparative neglect from which the ‘other man’ of Darwinism has suffered, it is the other man himself. (shrink)

The well-known argument against the Search for ExtraTerrestrial Intelligence (SETI) due to George Gaylord Simpson is re-analyzed almost half a century later, in the light of our improved understanding of preconditions for the emergence of life and intelligence brought about by the ongoing “astrobiological revolution”. Simpson’s argument has been enormously influential, in particular in biological circles, and it arguably fueled the most serious opposition to SETI programmes and their funding. I argue that both proponents and opponents of Simpson’s argument have (...) occasionally mispresented its core content. Proponents often oversimplify it as just another consequence of biological contingency, thus leaving their position open to general arguments limiting the scope of contingency in evolution (such as the recent argument of Geerat Vermeij based on selection effects in the fossil record). They also tend to neglect that the argument has been presented as essentially atemporal, while referring to entities and processes that are likely to change over time; this has become even less justifiable as our astrobiological knowledge increased in recent years. Opponents have failed to see that the weaknesses in Simpson’s position could be removed by restructuring of the argument; I suggest one way of such restructuring, envisioned long ago in the fictional context by Stanislaw Lem. While no firm consensus has emerged on the validity of Simpson’s argument so far, I suggest that, contrary to the original motivation, today it is less an anti-SETI argument, and more an astrobiological research programme. In this research programme, SETI could be generalized into a platform for testing some of the deepest assumptions about evolutionary continuity and the relative role of contingency versus convergence on unprecedented spatial and temporal scales. (shrink)