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The richness of life, Stephen Jay Gould

  1. The richness of life Stephen Jay Gould
  2. The evolution of life “Science can, and does, strive to grasp nature’s factuality, but all science is socially embedded, and all scientists record prevailing “certainties”, however hard they may be aiming for pure objectivity. Darwin himself, in the closing lines of The Origin of Species, expressed Victorian social preference more than nature’s record in writing “All corporeal and mental endowments will tend to progress towards perfection” 2
  3. “Our conventional [sic] desire to view history as progressive, and to see humans as predictably dominant, has grossly distorted our interpretation of life’s pathway by falsely placing in the center of things a relatively minor phenomenon that arises only as a side consequence of a physically constrained starting point. The most salient feature of life has been the stability of its bacterial mode from the beginning of the fossil record until today” 3
  4. “Our impression that life evolves toward greater complexity is probably only a bias inspired by parochial focus on ourselves, and consequent overattention to complexifying creatures, while we ignore just as many lineages adapting equally well by becoming simpler in form” 4
  5. The evolution of life “Three billion years of unicellularity, followed by five million years of intense creativity and then capped by more than 500 million years of variation on set anatomical themes can scarcely be read as a predictable, inexorable or continuous trend toward progress or increasing complexity. We do not know why the Cambrian explosion could establish all major anatomical designs so quickly” 5
  6. “An external explanation based on ecology seems attractive: the Cambrian explosion represents an initial filling of the “ecological barrel” of niches for multicellular organisms, and any experiment found a space. The barrel has never emptied since. But an internal explanation based on genetics also seems necessary as a complement: the earliest multicellular animals may have maintained a flexibility for genetic change and embryological transformation that became greatly reduced as organisms “locked in” to a set of stable and successful designs” 6
  7. Exaptation “Strict adaptation entails a paradox for students of evolutionary change. If all structures are well designed for immediate use, where is the flexibility for substantial change in response to severely altered environments?” Preadaptation does not cover the large class of structures that never were adaptations for anything, but arose as the numerous nonadaptive sequelae of primary adaptations” 7
  8. “The major basis of flexibility must lie in nonadaptation. Increased complexity implies a vastly greater range of nonadaptive sequelae for any change, and hence a greatly enlarged exaptive pool” 8
  9. “The scheme of punctuated equilibrium: lineages change little during most of their history, but events of rapid speciation occasionally punctuate this tranquility. Evolution is the differential survival and deployment of these punctuations. If gradualism is more a product of Western thought than a fact of nature, then we should consider alternate philosophies of change to enlarge our realm of constraining prejudices” 9
  10. “I make a simple plea for pluralism in guiding philosophies, and for the recognition that such philosophies, however hidden and unarticulated, constrain all our thought” 10
  11. Punctuated equilibrium “[In punctuated equilibrium], punctuation must be scaled relative to the later duration of species in stasis, and we suggest 1 to 2 percent (analogous to human gestation vs. the length of human life) as an upper bound. Punctuated equilibrium can be distinguished by the criterion of ancestral survival following the branching of a descendant” 12
  12. Punctuated equilibrium “Stasis is not defined as absolute phenotypic immobility, but as fluctuation of means through time at a magnitude not statistically broader than the range of geographic variation among modern populations of similar species, and not directional in any preferred way, especially not towards the phenotype of descendants. Gradualism certainly can and does occur, but at very low relative frequencies when all species of a fauna are tabulated, and when we overcome our bias for studying only the small percentage of species qualitatively recognized beforehand as having changed through time” 13
  13. The episodic nature of evolutionary change “Natura non facit saltum: Nature does not make leaps. Darwin portrayed evolution as a stately and orderly process, working at a speed so slow that no person could hope to observe it in a lifetime”. Huxley felt that Darwin was digging a ditch for his own theory. Natural selection required no postulate about rates” 14
  14. “On issues so fundamental as a general philosophy of change, science and society usually work hand in hand. The static systems of European monarchies won support from legions of scholars as the embodiment of natural law” 15
  15. “The history of most fossil species includes two features particularly inconsistent with gradualism: Stasis: Most species exhibit no directional change during their tenure on earth. Morphological change is usually limited and directionless. Sudden appearance: In any local area, a species does not arise gradually by the steady transformation of its ancestors, it appears all at once and ‘fully formed’” 16
  16. “Evolution proceeds in two major modes. In the first, phyletic transformation, an entire population changes from one state to another. [It] yields no increase in diversity. Since extinction is so common, a biota with no mechanism for increasing diversity would soon be wiped out. The second mode, speciation, replenishes the earth. New species branch off from a persisting parental stock. Eldredge and I believe that speciation is responsible for almost all evolutionary change. The way in occurs virtually guarantees that sudden appearance and stasis shall dominate the fossil record” 17
  17. “All major theories of speciation maintain that splitting takes place rapidly in very small populations. The theory of geographic, or allopatric, speciation is preferred by most evolutionists for most situations. A new species can arise when a small segment of the ancestral population is isolated at the periphery of the ancestral range. Large, stable central populations exert a strong homogenizing influence. New and favorable mutations are diluted by the sheer bulk of the population through which they must spread” 18
  18. “But small, peripherally isolated groups are cut off from their parental stock. They live as tiny populations in geographic corners of the ancestral range. Selective pressures are usually intense because peripheries mark the edge of ecological tolerance for ancestral forms. Favorable variations spread quickly. Small, peripheral isolates are a laboratory of evolutionary change” 19
  19. Betting on chance “The most serious of all misunderstandings between technical and vernacular haunts the concepts of probability and particularly the words random and chance. Ironically, the scientific sense of random conveys… maximal simplicity, order, and predictability –at least in the long run.” 20
  20. “Stability is far more common than change at any moment in the history of life. In its ordinary everyday mode, natural selection must struggle to preserve working combinations against a constant input of deleterious mutations. Natural selection must usually be “purifying” or “stabilizing”. Positive selection for change must be a much rarer event than watchdog selection for tossing out harmful variants and preserving what works” 21
  21. 22 “I do not challenge the statement that the most complex creature has tended to increase in elaboration through time, but I fervently deny that this limited little fact can provide an argument for general progress as a defining thrust of life’s history. Such a grandiose claim represents a ludicrous case of the tail wagging the dog, or the invalid elevation of a small and epiphenomenal consequence into a major and controlling cause”
  22. The ladder and the cone “Scientists view our pictures only as ancillary illustrations of what we defend by words. Few scientists would view an image itself as intrinsically ideological in content. Pictures, as accurate mirrors of nature, just are. Many of our pictures are incarnations of concepts masquerading as neutral descriptions of nature. These are the most potent sources of conformity, since ideas passing as descriptions lead us to equate the tentative with the unambiguously factual. Guesses and hunches become things” 23
  23. The ladder and the cone “The fatuous idea of a single order amidst the multifarious diversity of modern life flows from our conventional iconographies and the prejudices that nurture them –the ladder of life and the cone of increasing diversity. By the ladder, horseshoe crabs are judged as simple; by the cone, they are deemed old. And one implies the other under the grand conflation discussed above –down on the ladder also means old, while low on the cone denotes simple” 25
  24. “The familiar iconographies of evolution are all directed –sometimes crudely, sometimes subtly- toward reinforcing a comfortable view of human inevitability and superiority. We now know that the vast majority of “simpler” creatures are not human ancestors or even prototypes, but only collateral branches on life’s tree.” 26
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  26. Up against a wall “It just feels ‘right’ to us that the very earliest art should be primitive. Older in time should mean more and more rudimentary in mental accomplishment. [But] most individual species don’t alter much during their geological lifetimes. Large, widespread, and successful species tend to be specially stable. Humans fall into this category, and the historical record supports such a prediction. Human bodily form has not altered appreciably in 100,000 years. Cro-Magnon cave painters are us –so why should their mental capacity differ from ours? We don’t regard Plato or King Tut as dumb, even though they lived a long time ago.” 28
  27. Pervasive influence: Racism “The primitive-as-child argument stood second to none in the arsenal of racist arguments supplied by science to justify slavery and imperialism. I do not think that most scientists who upheld this argument intended to promote racism. They merely expressed their allegiance to the prevailing views of white intellectuals and leaders of European society. Biological arguments based on innate inferiority spread rapidly after evolutionary theory permitted a literal equation of modern “lower” races with ancestral stages of higher forms” 29
  28. 30 “Biological arguments for racism may have been common before 1859, but they increased by orders of magnitude following the acceptance of evolutionary theory. The litany is familiar: cold, dispassionate, objective, modern science shows us that races can be ranked on a scale of superiority”
  29. “Ultra-Darwinism… a conviction that natural selection regulates everything of any importance in evolution, and that adaptation emerges as a universal result and ultimate test of selection’s ubiquity. The irony is twofold. First, Darwin himself opposed the ultras of his own day. Second, the invigoration of modern evolutionary biology with exciting non- selectionist and non-adaptationist data makes our pre-millennial decade an especially unpropitious time for Darwinian fundamentalism” 31
  30. “But selection cannot suffice as a full explanation for many aspects of evolution: for other types and styles of causes become relevant, or even prevalent, in domains both far above and far below the traditional Darwinian locus of the organism. These additional principles are as directionless, non-teleological and materialistic as natural selection itself –but they operate differently” 32
  31. “How can we possibly know in detail what small bands on hunter-gatherers did in Africa two million years ago? These ancestors left some tools and bones. But how can we possibly obtain the key information that would be required to show the validity of adaptive tales: relations of kinship, social structures and sizes of groups, activities of males and females… and a hundred other central aspects of human life that cannot be traced in fossils?” 33 More things in heaven & earth
  32. Spandrels “Spandrels are the tapering triangular spaces formed by the intersection of two rounded arches at right angles. They are necessary architectural by-products of mounting a dome on rounded arches. Such architectural constraints abound and we find them easy to understand because we do not impose our biological biases upon them… Since the spaces must exist, they are often used for ingenious ornamental effect. The internal error of adaptationism arises from a failure to recognize that even the strictest operation of pure natural selection builds organisms full of nonadaptive parts and behaviors. Non-adaptations arise for many reasons in Darwinian systems, but consider only my favorite principle of ‘spandrels’” 34
  33. 35 “Many, if not most, universal behaviors are probably spandrels, often co-opted later in human history for important secondary functions. The human brain is the most complicated device for reasoning and calculating, and for expressing emotion, ever evolved on earth. Natural selection made the human brain big, but most of our mental properties and potentials may be spandrels –that is, non-adaptive side consequences of building a device with such structural complexity”
  34. “We live in a world of enormous complexity in organic design and diversity –a world where some features of organisms evolved by an algorithmic form of natural selection, some by an equally algorithmic theory of unselected neutrality, some by the vagaries of history’s contingency, and some as by-products of other processes. Why should such a complex and various world yield to one narrowly construed cause? 36
  35. Posture maketh the man “Upright posture frees the hands from locomotion and for manipulation. For the first time, tools and weapons can be fashioned and used with ease. Increased intelligence is largely a response to the enormous potential inherent in free hands for manufacture” 37
  36. The most unkindest cut of all “Claptrap and bogus Darwinian formulations have been used to justify every form of social exploitation –rich over poor, technologically complex over traditional, imperialist over aborigine, conqueror over defeated in war. Every evolutionist knows this history only too well, and we bear some measure of collective responsibility for the uncritical fascination that many of us have shown for such unjustified extensions” 38
  37. Excerpts by Ricardo Sosa