American Paleontologist, Evolutionary Biologist and Historian of Science
Stephan Jay Gould
American Paleontologist, Evolutionary Biologist and Historian of Science
Evolution is an inference from thousands of independent sources, the only conceptual structure that can make unified sense of all this disparate information.
Geoffrey also recognized that the opposite orientations of gut and nervous system posed a problem for his claim that insects and vertebrates represent different versions of the same archetypal animal - and he proposed the first account of the inversion theory to resolve this threat to unification. ...Geoffroy pursued the... aim of establishing a unity of type that could generate both arthropods and vertebrates from the same basic blueprint. ...The single grand design includes a gut in the middle and the main nerve cords somewhere on the periphery.
Humans arose, rather, as a fortuitous and contingent outcome of thousands of linked events, any one of which could have occurred differently and sent history on an alternative pathway that would not have led to consciousness.
I do not think that, practically or morally, we can defend a policy of saving every distinctive local population of organisms. I can cite a good rationale for the preservation of species, for each species is a unique and separate natural object that, once lost, can never be reconstituted. But subspecies are distinctive local populations of species with broader geographic range. Subspecies are dynamic, interbreedable, and constantly changing: what then are we saving by declaring them all inviolate?
I want to argue that the ‘sudden’ appearance of species in the fossil record and our failure to note subsequent evolutionary change within them is the proper prediction of evolutionary theory as we understand it. Evolution usually proceeds by ‘speciation’—the splitting of one lineage from a parental stock—not by the slow and steady transformation of these large parental stocks. Repeated episodes of speciation produce a bush. Evolutionary ‘sequences’ are not rungs on a ladder, but our retrospective reconstruction of a circuitous path running like a labyrinth, branch to branch, from the base of the bush to a lineage now surviving at its top. How does speciation occur? This is a perennial hot topic in evolutionary theory, but most biologist would subscribe to the ‘allopatric theory’ (the debate centers on the admissibility of other modes; nearly everyone agrees that allopatric speciation is the most common mode). Allopatric means ‘in another place.’ In the allopatric theory, popularized by Ernst Mayr, new species arise in in very small populations that become isolated from their parental group at the periphery of the ancestral range. Speciation in these small isolates is very rapid by evolutionary standards—hundreds or thousands of years (a geological microsecond). Major evolutionary change may occur in these small isolated populations. Favorable genetic variation can quickly spread through them. Moreover, natural selection tends to be intense in geographically marginal areas where the species barely maintains a foothold. In large central populations, on the other hand, favorable variations spread very slowly, and most change is steadfastly resisted by the well-adapted population. Small changes occur to meet the requirements of slowly altering climates, but major genetic reorganizations almost always take place in the small, peripherally isolated populations that form new species.
If the resident zoologist of Galaxy X had visited the earth 5 million years ago while making his inventory of inhabited planets in the universe, he would surely have corrected his earlier report that apes showed more promise than Old World monkeys and noted that monkeys had overcome an original disadvantage to gain domination among primates. (He will confirm this statement after his visit next year—but also add a footnote that one species from the ape bush has enjoyed an unusual and unexpected flowering, thus demanding closer monitoring.)
In the great debates of early-nineteenth century geology, catastrophists followed the stereotypical method of objective science-empirical literalism. They believed what they saw, interpolated nothing, and read the record of the rocks directly.
Life is short, and potential studies infinite. We have a much better chance of accomplishing something significant when we follow our passionate interests and work in areas of deepest personal meaning.
No more harmful nonsense exists than [the] common supposition that deepest insight into great questions about the meaning of life or the structure of reality emerges most readily when a free, undisciplined, and uncluttered (read, rather, ignorant and uneducated) mind soars above mere earthly knowledge and concern.
Our discombobulated lives need to sink some anchors in numerical stability. (I still have not recovered from the rise of a pound of hamburger at the supermarket to more than a buck.)
Science simply cannot adjudicate the issue of God’s possible superintendence of nature.
Surely the mitochondrion that first entered another cell was not thinking about the future benefits of cooperation and integration; it was merely trying to make its own living in a tough Darwinian world
The giraffe's neck supposedly supplies a crucial example for preferring natural selection over Lamarckism as a cause of evolution. But Darwin himself (however wrongly by later judgement) did not deny the Lamarckian principle of inheritance for characters acquired by use or lost by disuse. He regarded the Lamarckian mechanism as weak, infrequent, and entirely subsidiary to natural selection, but he accepted the validity of evolution by use and disuse. Darwin does speculate about the adaptive advantage of giraffe's necks, but he cites both natural selection and Lamarckism as probable causes of elongation.
The net of science covers the empirical realm: what is the universe made of (fact) and why does it work this way (theory). The net of religion extends over questions of moral meaning and value.
The world is full of signals that we don't perceive. Tiny creatures live in a different world of unfamiliar forces. Many animals of our scale greatly exceed our range of perception for sensations familiar to us… What an imperceptive lot we are. Surrounded by so much, so fascinating and so real, that we do not see (hear, smell, touch, taste) in nature, yet so gullible and so seduced by claims for novel power that we mistake the tricks of mediocre magicians for glimpses of a psychic world beyond our ken. The paranormal may be a fantasy; it is certainly a haven for charlatans. But parahuman powers of perception lie all about us in birds, bees, and bacteria.
Truly grand and powerful theories… do not and cannot rest upon single observations. Evolution is an inference from thousands of independent sources, the only conceptual structure that can make unified sense of all this disparate information. The failure of a particular claim usually records a local error, not the bankruptcy of a central theory... If I mistakenly identify your father's brother as your own dad, you don't become genealogically rootless and created de novo. You still have a father; we just haven't located him properly.
We have become, by the power of a glorious evolutionary accident called intelligence, the stewards of life's continuity on earth. We did not ask for this role, but we cannot abjure it. We may not be suited to it, but here we are.
What constitutes the primordium of the adult parasite [Rhizocephala ]? What can be injected through the narrow opening of the dart's hypodermic device? ...Imagine going through such complexity as nauplius, cyprid, and kentrogon - and then paring yourself down to just a few cells for a quick and hazardous transition to the adult stage. What a minimal bridge at such a crucial transition! ...But other species have achieved the ultimate reduction to a single cell! The dart injects just one cell into the host's interior, and the two parts of the life cyle maintain their indispensable continuity by an absolutely minimal connection - as though, within the rhizocephalan life cycle, nature has inserted a stage analogous to the fertilized egg that establishes minimal connection between generations in ordinary sexual organisms.
All versions written for nonscientists speak of fused males as the curious tale of the anglerfish—just as we so often hear about the monkey swinging through the trees, or the worm burrowing through soil. But if nature teaches us any lesson, it loudly proclaims life's diversity. There ain't no such abstraction as the clam, the fly, or the anglerfish. Ceratioid anglerfishes come in nearly 100 species, and each has its own peculiarity.
Bacteria represent the world's greatest success story. They are today and have always been the modal organisms on earth; they cannot be nuked to oblivion and will outlive us all. This time is their time, not the age of mammals as our textbooks chauvinistically proclaim. But their price for such success is permanent relegation to a microworld, and they cannot know the joy and pain of consciousness. We live in a universe of trade-offs; complexity and persistence do not work well as partners.
Darwin grasped the philosophical bleakness with his characteristic courage. He argued that hope and morality cannot, and should not, be passively read in the construction of nature. Aesthetic and moral truths, as human concepts, must be shaped in human terms, not discovered in nature. We must formulate these answers for ourselves and then approach nature as a partner who can answer other kinds of questions for us—questions about the factual state of the universe, not about the meaning of human life. If we grant nature the independence of her own domain—her answers unframed in human terms—then we can grasp her exquisite beauty in a free and humble way. For then we become liberated to approach nature without the burden of an inappropriate and impossible quest for moral messages to assuage our hopes and fears. We can pay our proper respect to nature's independence and read her own ways as beauty or inspiration in our different terms.
Evolution is an obstacle course not a freeway; the correct analogue for long-term success is a distant punt receiver evading legions of would-be tacklers in an oddly zigzagged path toward a goal, not a horse thundering down the flat.
Giraffes do use their long necks to browse leaves, at the tops of acacia trees - but such current function, no matter how vital, does not prove that the neck originally evolved for this purpose. The neck may have first lengthened in context of a different use, and then been coopted for better dining when giraffes moved into the open plains. Or the neck may have evolved to perform several functions at once. We cannot learn the reasons for historical origin simply by listing current uses.
Hyper-selectionism has been with us for a long time in various guises; for it represents the late nineteenth century's scientific version of the myth of natural harmony—all is for the best in the best of all possible worlds (all structures well designed for a definite purpose in this case). It is, indeed, the vision of foolish Dr. Pangloss, so vividly satirized by Voltaire in Candide—the world is not necessarily good, but it is the best we could possibly have.
I emphatically do not assert the general ‘truth’ of this philosophy of punctuational change. Any attempt to support the exclusive validity of such a grandiose notion would border on the nonsensical… Nonetheless, I will confess to a personal belief that a punctuational view may prove to map tempos of biological and geographic change more accurately and more often than any of its competitors — if only because complex systems in steady state are both common and highly resistant to change. As my colleague British geologist Derek V. Ager writes in supporting a punctuational view of geologic change: ‘The history of any one part of the earth, like the life of a soldier, consists of long periods of boredom and short periods of terror.’