Yale University Alumni

"A major goal of investigating how cooperative norms in societal settings have been established is a better understanding of how to promote cooperative norms in international settings. This is not as utopian as it might seem because international norms against slavery and colonialism are already strong, while international norms are partly effective against racial discrimination, chemical warfare, and the proliferation of nuclear weapons. Because norms sometimes become established surprisingly quickly, there may be some useful cooperative norms that could be hurried along with relatively modest interventions."

"Tournament studies, ecological simulation, and theoretical analysis demonstrate: (1) A generous version of tit for tat is a highly effective strategy when the players it meets have not adapted to noise; (2) If the other players have adapted to noise, a contrite version of tit for tat is even more effective at quickly restoring mutual cooperation without the risk of exploitation; (3) Pavlov is not robust."

"In complex environments, individuals are not fully able to analyze the situation and calculate their optimal strategy. Instead they can be expected to adapt their strategy over time based upon what has been effective and what has not."

"A moral of the story is that models that aim to explore fundamental processes should be judged by their fruitfulness, not by their accuracy. For this purpose, realistic representation of many details is unnecessary and even counterproductive."

"Throughout the social sciences today, the dominant form of modeling is based upon the rational-choice paradigm. Game theory, in particular, is typically based upon the assumption of rational choice. In my view, the reason for the dominance of the rational-choice approach is not that scholars think it is realistic. Nor is game theory used solely because it offers good advice to a decision maker, because its unrealistic assumptions undermine much of its value as a basis for advice."

"The two-person iterated Prisoner’s Dilemma is the E. coli of the social sciences, allowing a very large variety of studies to be undertaken in a common framework."

"Proposition 2. TIT FOR TAT is collectively stable if and only if, w is large enough. This critical value of w is a function of the four payoff parameters, T; R, P, and S."

"What accounts for TIT FOR TAT's robust success is its combination of being nice, retaliatory, forgiving, and clear. Its niceness prevents it from getting into unnecessary trouble. Its retaliation discourages the other side from persisting whenever defection is tried. Its forgiveness helps restore mutual cooperation. And its clarity makes it intelligible to the other player, thereby eliciting long-term cooperation."

"In addition, TIT FOR TAT was known to be a powerful competitor. In a preliminary tournament, TIT FOR TAT scored second place; and in a variant of that preliminary tournament, TIT FOR TAT won first place. All of these facts were known to most of the people designing programs for the Computer Prisoner's Dilemma Tournament, because they were sent copies of a description of the preliminary tournament. Not surprisingly, many of them used the TIT FOR TAT principle and tried to improve upon it. The striking fact is that none of the more complex programs submitted was able to perform as well as the original, simple TIT FOR TAT."

"Proposition 1. If the discount parameter, w, is sufficiently high, there is no best strategy independent of the strategy used by the other player."

"In fact, in the Prisoner's Dilemma, the strategy that works best depends directly on what strategy the other player is using and, in particular, on whether this strategy leaves room for the development of mutual cooperation. This principle is based on the weight of the next move relative to the current move being sufHciently large to make the future important."

"What makes it possible for cooperation to emerge is the fact that the players might meet again. This possibility means that the choices made today not only determine the outcome of this move, but can also influence the later choices of the players. The future can therefore cast a shadow back upon the present and thereby affect the current strategic situation. But the future is less important than the present-for two reasons. The first is that players tend to value payoffs less as the time of their obtainment recedes into the future. The second is that there is always some chance that the players will not meet again. An ongoing relationship may end when one or the other player moves away, changes jobs, dies, or goes bankrupt. For these reasons, the payoff of the next move always counts less than the payoff of the current move."

"The Cooperation Theory that is presented in this book is based upon an investigation of individuals who pursue their own self-interest without the aid of a central authority to force them to cooperate with each other. The reason for assuming self-interest is that it allows an examination of the difficult case in which cooperation is not completely based upon a concern for others or upon the welfare of the group as a whole. It must, however, be stressed that this assumption is actually much less restrictive than it appears."

"Proposition 5. ALL D is always collectively stable."

"Proposition 4. For a nice strategy to be collectively stable, it must be provoked by the very first defection of the other player."

"Proposition 3. Any strategy which may be the first to cooperate can be collectively stable only when w is sufficiently large."

"The more that we learn about these animals the more we find that there is basically no difference between birds and their closely related dinosaur ancestors like velociraptor. Both have wishbones, brooded their nests, possess hollow bones, and were covered in feathers. If animals like velociraptor were alive today our first impression would be that they were just very unusual looking birds."

"If you look at crocodiles today, they aren’t really representative of what the lineage of crocodiles look like. Crocodiles are represented by about 23 species, plus or minus a couple. Along that lineage the more primitive members weren’t aquatic. A lot of them were bipedal, a lot of them looked like little dinosaurs. Some were armored, others had no teeth. They were all fully terrestrial. So this is just the last vestige of that radiation that we’re seeing. And the ancestor of both dinosaurs and crocodiles would have, to the untrained eye, looked much more like a dinosaur."

"If you saw a baby tyrannosaur you would probably think it was a weird looking bird. A full grown one might have had feathers too, maybe not on its whole body though, maybe more of an ornamental display sort of feathers. So traits in the theropod dinosaurs were more birdlike than say, crocodiles."

"Really the best way to understand anything about dinosaurs is by looking at living animals. You look at birds and then look at the closest living ancestor of birds, which is the crocodile. If you look at characteristics that birds and crocodiles have in common, the explanation is that the trait was in the common ancestor that birds and crocodiles had at one time."

"We have as much evidence that T. rex was feathered, at least during some stage of its life, as we do that australopithecines like Lucy had hair."

"A couple things that we do know about theropods—the ones that most closely related to birds—is that they brooded their nests. If you go deeper in the tree, what you see is that for sauropods, we have no direct evidence that they returned to the nest after the eggs were laid. Most of the evidence for that comes from an excavation in Argentina called Auca Mahuevo. What’s thought with sauropods is that they’d just lay a bunch of eggs and leave them alone—the turtle model. Few of those would ever reach adulthood."

"When people look of non-avian dinosaur they’re thinking of extrapolating a cow up to that size. Mammals are much much denser than birds are, because a lot of the skeletons of sauropods (the big, long-necked ones—Apatosaurus, Brachiosaurus and the like) and theropod dinosaurs are just air. Theropods don’t have solid bones like we do; they have hollow bones. Sauropods don’t, but they have tremendous air sacs that fill up a lot of their bodies. And thus they weigh way less than a mammal scaled up to that size."

"Humans are proud of themselves. The guiding principle of the modern age is "Man is the measure of all things." And our bodies have excited physiologists and philosophers to a profound awe of the basic mammalian design. But the history of the dinosaurs should teach us some humility... If our fundamental mammalian mode of adaptation was superior to the dinosaurs', then history should record the meteoric rise of the mammals and the eclipse of the dinosaurs. Our own Class Mammalia did not seize the dominant position in life on land. Instead, the mammal clan was but one of many separate evolutionary families that succeeded as species only by taking refuge in small body size during the Age of Dinosaurs. As long as there were dinosaurs, a full 130 million years, remember, the warm-blooded league of furry mammals produced no species bigger than a cat."

"Without doubt the most dangerous devices for active defense among the Dinosauria emerged in Triceratops. The scene has been portrayed in paintings, drawings, and illustrations hundreds of times, but it remains thrilling. Tyrannosaurus, the greatest dinosaur toreador, confronts Triceratops, the greatest set of dinosaur horns. No matchup between predator and prey has ever been more dramatic. It's somehow fitting that those two massive antagonists lived out their co-evolutionary belligerence through the very last days of the very last epoch in the Age of Dinosaurs. Tyrannosaurus stood over twenty feet tall when fully erect, and a large adult was as heavy as a small elephant - five tons. No predatory dinosaur, no predatory land animal of any sort, had more powerful jaws. Withstanding a Tyrannosauruss attack required either tanklike armor – the approach taken by Ankylosaurus – or most powerful defensive weapons - the approach taken by Triceratops."

"Plants and plant-eaters co-evolved. And plants aren't the passive partners in the chain of terrestrial life. Hence today's Pop Ecology movement is quite wrong in believing that plants are happy to fill their role as fodder for herbivores in a harmonious and perfectly balanced ecosystem. A birch tree doesn't feel cosmic fulfillment when a moose munches its leaves; the tree species, in fact, evolves to fight the moose, to keep the animal's munching lips away from vulnerable young leaves and twigs. In the final analysis, the merciless hand of natural selection will favor the birch genes that make the tree less and less palatable to the moose in generation after generation. No plant species could survive for long by offering itself as unprotected fodder."

"No living reptile has cheeks. But no living reptile has grinding teeth anything remotely resembling those of a duckbill. If the duckbills could have evolved such unreptilian teeth, why couldn't they have evolved unreptilian teeth?"

"There may be some ground for believing that brontosaurs ate... soft foods. If the possibility of gizzard stones is ignored, the brontosaurs' dentition does seem little equipped to deal with meals of tougher plants. But there are no ground whatsoever for believing it of duckbills. The mouth of a duckbill dinosaur contained one of the efficient cranial Cusinarts in land-vertebrate history. Duckbill teeth and jaws were incomparable grinders, designed to cope with foods right inside the duckbill's oral compartment."

"The sum of evolutionary evidence is thoroughly damning. In nearly every modification of the evolutionary process made in the duckbills as they developed from their dryosaur ancestors, the duckbills suffered a diminution of their swimming potential. Their fore- and hind paws became shorter and more compact, not longer and more widely spread. Their tails got weaker and stiffer. Far from being the best, the duckbills must have been the clumsiest and slowest swimmers in all the Dinosauria. If pressed, they probably could paddle slowly from one riverbanck to another. The central theme of their bodily evolution was indeed specialized - orthodox theory was right on that point - but the direction of specialization was landward. These dinosaurs were specialized for a totally terrestrial existence."

"Duckbills were supposedly croc-style swimmers, moving by strong, easy, side-to-side flexures of their tail. Therefore, the optimal design would feature vertical tail spines. But duckbill spines all slanted strongly backward, exactly as in land-living lizards, not in swimmers. Another problem in the duckbill's swimming equipment lies in the profile of the tail. The deepest part of the croc's tail is close to the end, because the end swings through a wider arc than does the base in moving side to side. Thus the tail is deepest where it can do the most good in pushing against the water. All powerful tail-scullers have such deep tail ends. But duckbill tails were deepest at the hips and become progressively narrower from top-to-bottom toward the tip - another caudal feature nearly totally maladapted for its primary function."

"By themselves, brontosaur gizzards don't indicate how much or what these dinosaurs ate each day; other lines of evidence must be employed to explore these questions. But brontosaur gizzards and teeth together indicate what brontosaurs did not eat. They didn't eat soft, mushy vegetation. Birds that subsist entirely on soft fruits don't possess muscular gizzards and don't use hard pebbles for their gizzard linings. Soft, watery food requires only a short, simply constructed gut - with just enough contractile force to squeeze out all the juices. Brontosaur teeth, moreover, confirm the heretical idea that they ate a tough vegetable diet. If the brontosaurs dined only on soft water plants, then very little wear would be found on their teeth. But in fact the teeth of Camarasaurus, Brachiosaurus, and their kin manifest very severe wear, which could only have been produced by tough or gritty food."

"Both birds and crocs have the identical plan to their specialized gizzard apparatus, and this type of internal food processor is absent in the other "reptiles" - lizards, snakes, and turtles."

"Zoos mislead their visitors by the way the species are housed. Birds are in the Bird House, of course, and crocodiles are always segregated to the Reptile House with the other naked-skinned, scale-covered brutes. So the average visitor leaves the zoo firmly persuaded that crocodilians are reptiles while birds are an entirely different group defined by "unreptilian" characteristics - feathers and flight. But a turkey's body and a croc's body laid out on a lab bench would present startling evidence of how wrong the zoos are once the two stomachs were cut into. The anatomy of their gizzards is strong evidence that crocodilians and birds are closely related and should be housed together in zoological classification, if not in zoo buildings."

"The message from the tropics is unambiguous: To be a successful big land animal, you must cope with mammals, and to cope with mammals you must be a mammal yourself, or at least have metabolism as high as a mammal's. And big mammals have suppressed big reptiles in our tropics for the last sixty-five million years. So how can the dinosaurs' success over mammals' be explained? By assuming that dinosaurs had low-energy metabolic styles? Not very likely."

"Giant predator lizards can't evolve in the presence of big mammal predators. So the lesson is that mammals suppress much of the evolutionary potential of modern lizards. Is the Komodo dragon a good working model of how dinosaurs succeeded? Absolutely not. Dinosaurs suppressed the evolutionary potential of mammals, not the other way around. And dinosaurs carried out this supression everywhere, on all the continents, not merely on a few tiny tropical isles. Dinosaurs succeeded where Komodo dragons fail."

"Our own mammalian order, the primates, prides itself on hand-eye coordination, monkeys, apes, and man are all good manipulators. But no mammal can rival the chameleon for eye-tongue coordination."

"Up to eight feet long and as heavy as a lioness, the adult Komodo dragon brandishes steak-knifelike teeth - sharp, recurved blades with serrated cutting edges. Showing the same sagacity found in veteran Nile crocodiles, fully adult dragons know their hunting territory from years of experience. They know where to lie along hilly game trails, awaiting the light footsteps of a deer. Attacks are instant successes or failures because the ora has no stamina, and if it misses on the first short rush, it has little sustained speed for a long pursuit. When an attack succeeds, the cruel rows of slashing teeth cut fearful wounds on the rump and thigh of ambushed animals and the stricken prey may die of massive infection days later even if it manages to break free from the dragon's mouth. Tethered livestock suffer truly terrible cuts across the legs when an ora slinks into the compound under cover of the warm Indonesian nights. Several humans, both native and European visitors, have died in savage daylight attacks. The victims simply had no warning sign that the ora was waiting patiently a few feet from the trail's edge."

"The total turtle count - two hundred and thirty species - doesn't seem like an irresistible horde compared to the several thousand mammals in today's global ecosystem. However, turtles have scored quite an impressive ecological triumph in one very important role, that of freshwater predator-omnivore... All through the Temperate Zone, otters delight the naturalist and the lay public. But how many other freshwater, semi-aquatic mammal predators can you name? Mink, of course. Relatives of otters on one hand, land weasels on the other, mink do hunt in streams. How many others? If you caught the excellent BBC series "Life on Earth", you saw footage of the swimming shrew, the Desman of the Pyrenees, a molelike furball that dives for aquatic worms and other freshwater small fry. Our own New England star-nosed mole goes hunting in water, using its starburst-shaped snout tip to feel out wriggling prey. Andean streams flowing through Preu are host to the fish-spearing mouse, Ichthyomys, that impales prey on its projecting front teeth. But if we go to a tropical lake or sluggish river, is it full of otters, mink, and paddling shrews? No, it is full of turtles."

"No one, either in the nineteenth century or the twentieth, has ever built a persuasive case proving that dinosaurs as a whole were more like reptilian crocodiles than warm-blooded birds. No one has done this because it can't be done."

"Dinosaurs are not lizards, and vice versa. Lizards are scaley reptiles of an ancient bloodline. The oldest lizards antedate the earliest dinosaurs by a full thirty million years. A few large lizards, such as the man-eating Komodo dragon, have been called "relicts of the dinosaur age", but this phrase is historically incorrect. No lizard ever evolved the birdlike characteristics peculiar to each and every dinosaur. A big lizard never resembled a small dinosaur except for a few inconsequential details of the teeth. Lizards never walk with the erect, long-striding gait that distinguishes the dinosaurlike ground birds today or the birdlike dinosaurs of the Mesozoic."

"Twentieth-century paleontologists have fallen into the bad habit of reconstructing the dinosaurs' life functions by using crocodiles as a living model. But the earliest researchers of the nineteenth century proved beyond a doubt that the dinosaurs' powerful hind limbs must have operated like the limbs of gigantic birds."

"If we measured success by longevity, then dinosaurs must rank as the number one success story in the history of land life. Not only did dinosaurs exercise an airtight monopoly as large land animals, they kept their commanding position for an extraordinary span of time - 130 million years. Our own human species is no more than a hundred thousand years old. And our own zoological class, the Mammalia, the clan of warm-blooded furry creatures, has ruled the land ecosystem for only seventy million years. True, the dinosaurs are extinct, but we ought to be careful in judging them inferior to our own kind. Who can say that the human system will last another thousand years, let alone a hundred million? Who can predict that our Class Mammalia will rule for another hundred thousand millennia?"

"The dinosaurs are not extinct. The colorful and successful diversity of the living birds is a continuing expression of basic dinosaur biology."

"I do not be­lieve birds deserve to be put in a taxo­nomic class separate from dinosaurs."

"When the dinosaurs fell at the end of the Cretaceous, they were not a senile, moribund group that had played out its evolutionary options. Rather they were vigorous, still diversifying into new or­ders and producing a variety of big­brained carnivores with the highest grade of intelligence yet present on land."

"One might expect that mammals would have taken over the land verte­brate communities immediately, but they did not. From their appearance in the Triassic until the end of the Creta­ceous, a span of 140 million years, mam­mals remained smal and inconspicuous while all the ecological roles of large ter­restrial herbivores and carnivores were monopolized by dinosaurs; mammals did not begin to radiate and produce large species until after the dinosaurs had al­ready become extinct at the end of the Cretaceous. One is forced to conclude that dinosaurs were competitively su­perior to mammals as large land vertebrates. And that would be baffling if dinosaurs were "cold-blooded." Perhaps they were not."

"Dinosaurs have a bad public image as symbols of obsolescence and hulking in­ inefficiency; in political cartoons they are know-nothing conservatives that plod through miasmic swamps to inevitable extinction."

"The dinosaur is for most people the epitome of extinctness, the proto­type of an animal so maladapted to a changing environment that it dies out, leaving fossils but no descendants."

"The classical view of dinosaurs presents a perplexing problem. The group of vertebrates which dominated the land before the rise of the dinosaurs were the synapsids, the mammal-like reptiles... Most paleontologists have believed that the locomotion and physiology of these mammal-like synapsids were more similar to those of active, warm-blooded mammals than to sluggish modern lizards or alligators. Surprisingly, though, when the first dinosaurs and their near relatives appeared in the Triassic period, the synapsids began to decline and soon became extinct. The dinosaurs then ruled the land unchallenged for over 100 million years while the early mammals, the surviving descendants of the synapsids, remained very small in size and number. Only after the dinosaurs suddenly disappeared about 70 million years ago did the mammals develop into the great variety of dominant land vertebrates we have today. The problem is this: if the later synapsids were such splendidly advanced animals with the improved physiology of mammals, and if dinosaurs were slow and sluggish, why were the mammal-like synapsids exterminated in competition with the first dinosaurs? And why didn't the mammals achieve a more significant diversification during the dinosaurs' reign?"

"Ceratosaurus is and has been my favorite dino since 1958. This is a minority taste. I’ve met only one dino-digger who rated it #1 in desirability."