This is the principle of the hypothetico-deductive method in science, as enunciated by Karl Popper in 1934. He could see the method extended to the historical sciences, but was a little unsure how. At first, it might seem to be forever impossible to discuss historical events, whether in archaeology, palaeontology, or geology, in a scientific manner. However, in this book, we have explored some examples where it works.
Theory and criticism
Scientists and non-scientists can often misunderstand the role of criticism. Of course, it is the duty of all observers to correct mistaken facts – so palaeontologists, and an army of online commentators, are quick to pick up mistakes in dating fossils, identifying specimens, measuring dimensions, reporting specific anatomical features and the like. Charles Darwin, who was right about so much, said this: ‘False facts are highly injurious to the progress of science, for they often endure long; but false views, if supported by some evidence, do little harm, for every one takes a salutary pleasure in proving their falseness.’
Criticism of hypotheses and theories is another matter. Indeed, as Darwin said, scientists do not hold back from criticizing the theories of others. But the critic cannot simply ridicule a particular theory and step back. It’s not like politics. The critic must present a more convincing theory that explains the data better than the theory he or she is criticizing. The business of being a scientist is rigorous, and the argument has to consider all evidence, and weigh up alternative hypotheses in an even-handed way.
This brings us to the idea of a ‘theory’. It’s true in English, and in many other languages, that the term ‘theory’ has two meanings. In common speech, a ‘theory’ can be a notion, such as ‘my theory is that we’ll have sausages for supper tonight…and it’s my neighbour’s dog that is messing the garden’. These are small-scale deductions, theories of a sort. In science, a theory is a model of how the world works, such as gravity or evolution (big theories) or the end-Cretaceous impact or the replacement of dinosaurs by mammals through competitive release (smaller theories). The evidence lines up, they have been repeatedly tested, they are robust, and there is no better theory around. As for the sausages or the dog, who knows? There could be a million alternative outcomes or explanations.
So, climate-change deniers and creationists and, in their time, the smoking-as-killer deniers, play with the word ‘theory’. ‘Oh, it’s just a guess’, they say. Their alternative perspectives, however, do not stand up to the evidence. That dinosaurs existed is a theory. So is gravity, and so is the germ theory of disease, and we’re prepared to risk our lives by flying in an aeroplane or going under the surgeon’s knife based on those theories – because they are real theories that have been stress-tested.
The transformation of dinosaur palaeobiology from speculation to science
In this book, we have been on a journey from 1980 to the present day, and we have stopped off at some of the debates and controversies. In particular, we have looked at those cases where the experts in the past could only really speculate and give an opinion, and how those fields have been transformed into science.
We saw how the evolutionary tree and classification of dinosaurs were transformed from 1984 onwards by the application of cladistic methods – and how the debates were reignited in 2017 with a radical new tree of dinosaurs. We have seen how those trees are the basis for the application of new methods in the study of evolution to look for fast and slow rates of change, and even the kinds of models of evolution, including the tension, triggered by one of our papers in 2016, about whether or not dinosaurs were somehow on the way out long before the asteroid struck.
Indeed, the idea that dinosaurs were exterminated by the consequences of the impact of a huge asteroid, proposed in 1980, and tested hard ever since, has led to the most extraordinary revitalization of many fields of science.
And, as we have seen, it’s not just evolutionary trees and events that have been rethought, but also palaeobiology. New engineering approaches have revolutionized the ways in which dinosaurologists investigate feeding and locomotion, and close observations of bone histology allow us to make some conclusions about growth and physiology. Most remarkable of all, arguably, was the discovery of the colours and patterns of dinosaur feathers in 2010, and the implications of that discovery for our understanding of sexual behaviour and perhaps the role of sexual selection in dinosaur evolution.
What next?
What next? Ten years ago, I would have said that for sure we would never know the colour of dinosaurs. Now we do – well, some at least, and based on a solid line of reasoning. So, we now have the melanosome theory for ancient colour. Perhaps we don’t know the noises dinosaurs made. Also, it seems unlikely we can ever find dinosaur DNA or clone a dinosaur…Still, should we say ‘never’?
Advances in methods of chemical analysis, and experimental approaches, are improving our knowledge of which organic molecules are capable of surviving the rigours of fossilization. Some, such as melanin, can survive, and other dinosaur molecules such as proteins might provide sequence information that could be used to test relationships in evolutionary trees. We have only just begun CT scanning and engineering analysis of fossils, and much new information about how dinosaurs moved and fed will emerge. Another growth field is number-crunching of evolutionary patterns and processes on supertrees, and new methods will lead to new discoveries. Microscopic studies of bone will tell us more about dinosaur growth and sex, and tooth-wear patterns may confirm ideas about diet.
Scientists and the public are understandably fascinated by the extinction of the dinosaurs and how and why it happened. Surely, of equal fascination is the rather obscure origin of the dinosaurs. We have seen how new fossils have pushed the date of origin back from 230 million years ago to 245 million years ago, and – who knows? – future researchers may push it back even further. We have also seen that in their origin dinosaurs were playing out a complex ecological story, and we are only now getting to grips with it. As we saw, there’s a fundamental tension between competitive and opportunistic models – were dinosaurs driving their competitors to the wall and showing their progressive qualities, or were they the lucky beneficiaries of a series of grim environmental catastrophes? These are core questions about life on Earth, rates of change, and the role of climate change in driving evolution – all very current issues key to understanding the future fate of biodiversity.
In his 1998 book What Remains to be Discovered, John Maddox, veteran science commentator and editor, was quite clear that much remained to be discovered in science, and each new discovery leads to fresh questions. The same is undoubtedly true of palaeobiology and the science of dinosaurs. We eagerly await the wonders that will be brought to the table by new generations of researchers.
Appendix
Extinction Hypotheses
List of published hypotheses for the extinction of the dinosaurs. The date of first publication of each idea is given, where possible. Most of these ideas would be rated as ‘nonsense’, because there is no evidence. I highlight those ideas for which there is some evidence, and mark two that are plausible contributors to the mass-extinction theory in bold. These ideas are fully described and referenced in a paper I wrote years ago (Benton, M.J. 1990. Scientific methodologies in collision: the history of the study of the extinction of the dinosaurs. Evolutionary Biology, 24, 371–424).
1. Biological causes
A.‘Medical problems’
A1.Metabolic disorders
01.Slipped vertebral discs
02.Malfunction or imbalance of hormone systems
01.Overactivity of pituitary gland and excessive growth of bones and cartilage [1917]
02.Malfunction of pituitary gland leading to excess growth of debilitating horns, spines, and frills [1910]
03.Imbalances of vasotocin and oestrogen levels leading to pathological thinning of egg shells [1979]
03.Diminution of sexual activity [1917]
04.Cataract blindness [1982]
; 05.Disease: caries, arthritis, fractures, and infections reached a maximum in Late Cretaceous reptiles [1923]
06.Epidemics
07.Parasites
08.AIDS caused by increasing promiscuity [1986]
09.Change in ratio of DNA to cell nucleus
A2.Mental disorders
01.Dwindling brain and consequent stupidity [1939]
02.Absence of consciousness and ability to modify behaviour [1979]
03.Development of psychotic suicidal factors
04.Paleoweltschmerz: boredom with the ancient world
A3.Genetic disorders: excessive mutation rate induced by high levels of cosmic rays and/or ultraviolet light, leading to small population size burdened by a high genetic load, and consequent vulnerability to environmental shock [1987]
B.Racial senility
01.Evolutionary drift into senescent overspecialization, as evinced in gigantism and spinescence (e.g., loss of teeth, and ‘degenerate form’) [1910]
02.Racial old age [1964, Will Cuppy: ‘the Age of Reptiles ended because it had gone on long enough and it was all a mistake in the first place’]
C.Biotic interactions
C1.Competition with other animals
01.Competition with the mammals – invasion of North America by Asian mammals [1922]
02.Competition with caterpillars, which ate all the plants [1962]
C2.Predation
01.Overkill capacity by predators (the theropods ate themselves out of existence)
02.Egg-eating by mammals, which reduced hatching success of the young [1925]
C3.Floral changes
01.Spread of flowering plants and reduction in availability of conifers, ferns, etc. This led to a reduction of fern oils, and to lingering death by terminal constipation [1964]
02.Floral change and loss of marsh vegetation [1922]
03.Floral change and increase in forests [1981]
04.Reduction in availability of plant food as a whole
05.Presence of poisonous tannins and alkaloids in the flowering plants [1976]
06.Presence of other poisons in plants
07.Lack of calcium and other necessary minerals in plants
08.Rise of flowering plants, and of their pollen, leading to extinction of dinosaurs by hay fever [1983]
2. Physical environmental causes
D.Terrestrial explanations
D1.Climatic change
01.Climate became too hot as a result of high levels of carbon dioxide in the atmosphere, and the ‘greenhouse effect’; extinction was caused by the high temperature and increased aridity [1946], which either inhibited spermatogenesis [1945], unbalanced the male:female ratio of hatchlings [1982], killed off juveniles [1949], or led to overheating in summer, especially if the dinosaurs were warm-blooded [1978]
02.Climate became too cold, and this led to extinction because it was too cold for embryonic development [1929], because the endothermic dinosaurs lacked insulation and could not maintain a constant body temperature [1965], and they were also too large to hibernate [1967], or, even if they were warm-blooded, the cold winter temperatures finished them off [1973]
03.Climate became too dry [1946]
04.Climate became too wet
05.Reduction in climatic equability and increase in seasonality [1968]
D2.Atmospheric change
01.Changes in the pressure or composition of the atmosphere (e.g. excessive amounts of oxygen from photosynthesis) [1957]
02.High levels of atmospheric oxygen, leading to fires following an extraterrestrial impact [1987]
03.Low levels of carbon dioxide, removing the ‘breathing stimulus’ of dinosaurs [1942]
04.Excessively high levels of carbon dioxide in the atmosphere and asphyxiation of dinosaur embryos in the eggs [1978]
05.Extensive volcanism and the production of volcanic dust
06.Poisoning by selenium from volcanic lava and dust [1967]
07.Toxic substances in the air, possibly produced from volcanoes, which caused thinning of dinosaur egg shells [1972]
D3.Oceanic and topographic change
01.Sea level fall and drying of continental interiors [1964]
02.Lowering of global sea level leading to dinosaur extinction, on the assumption that they were underwater organisms [1949]
03.Floods
04.Mountain building, for example, the Laramides in North America [1921]
05.Drainage of swamp and lake habitats [1939]
06.Stagnant oceans caused by high levels of carbon dioxide [1983]
07.Loss of oxygen on the sea bed at start of sea level advance [1984]
08.Spillover of Arctic water (fresh) from its formerly enclosed condition into the oceans, which led to reduced temperatures worldwide [1978]
09.Reduced topographic relief, and reduction in terrestrial habitats [1968]
D4.Other terrestrial catastrophes
01.Eruption of the Deccan Traps [1982]
02.Fluctuation of gravitational constants
03.Shift of the Earth’s rotational poles
04.Extraction of the moon from the Pacific Basin and consequent world perturbation
05.Poisoning by uranium sucked up from the soil [1984]
E.Extraterrestrial explanations
01.Entropy; increasing chaos in the universe and hence loss of large organized life forms
02.Sunspots
03.Cosmic radiation and high levels of ultraviolet radiation [1928]
04.Destruction of the ozone layer by solar flares, letting in ultraviolet radiation [1954]
05.Ionizing radiation [1968]
06.Electromagnetic radiation and cosmic rays from the explosion of a nearby supernova [1971]
07.Interstellar dust cloud [1984]
08.Flash heating of atmosphere by entry of meteorite [1956]
09.Oscillations about the galactic plane [1970]
10.Impact of an asteroid, a comet, or comet showers (Luis Alvarez and colleagues, 1980)
Further Reading
Author’s note
Publications marked with an asterisk (*) provide easy introductions to the topic, and should be consulted first.
Some key publications described in the book are listed below for the dedicated scholar, or for anyone who wants to check up on what I have said. Brief comments after particular papers clarify any further details.
All quotations from individuals were provided directly to me by email, unless otherwise indicated in the text.
I also add a list of current dinosaur books that are all original and worth reading.
Introduction
How Scientific Discoveries Are Made
(pp. 8–20)
Benton, M. J. 2015. When Life Nearly Died. 2nd edition. Thames & Hudson, London and New York
*Magee, B. 1974. Popper. Routledge, London An excellent, short introduction to Karl Popper’s writings on philosophy, including the hypothetico-deductive method in science and his thoughts on the historical sciences.
Popper, K. R. 1934. Logik der Forschung. Mohr Siebeck, Tübingen [First English-language edition, The logic of scientific discovery, published by Routledge, London.]
Rhodes, F. H. T., Zim, H. S., and Shaffer, P. R. 1962. Fossils, a guide to prehistoric life. Golden Nature Guides, Golden Press, New York; Hamlyn, London
Witmer, L. M. 1995. The extant phylogenetic bracket and the importance of reconstructing soft tissues in fossils. In J. J. Thomason (ed.), Functional morphology in vertebrate paleontology, Cambridge University Press, Cambridge and New York, pp. 19–33
Chapter 1
Origin of the Dinosaurs
(pp. 21–51)
Benton, M. J. 1983. Dinosaur success in the Triassic: A noncompetitive ecological model. Quarterly Review of Biology 58, 29–55 My original paper that challenged the Romer-Colbert-Charig model for dinosaur origins by competitive relay.
Benton, M. J., Bernardi, M., and Kinsella, C. 2018. The Carnian Pluvial Episode and the origin of dinosaurs. Journal of the Geological
Society 175 (6), 1019
*Benton, M. J., Forth, J., and Langer, M. C. 2014. Models for the rise of the dinosaurs. Current Biology 24, R87–R95 A brief, but slightly technical, introduction to how we use numerical methods to explore the origin of dinosaurs.
Bernardi, M., Gianolla, P., Petti, F. M., Mietto, P., and Benton, M. J. 2018. Dinosaur diversification linked with the Carnian Pluvial Episode. Nature Communications 9, 1499: https://www.nature.com/articles/s41467-018-03996-1
Brusatte, S. L., Benton, M. J., Ruta, M., and Lloyd, G. T. 2008. Superiority, competition, and opportunism in the evolutionary radiation of dinosaurs. Science 321, 1485–88
*Brusatte, S. L., Nesbitt, S. J., Irmis, R. B., Butler, R. J., Benton, M. J., and Norell, M. A. 2010. The origin and early radiation of dinosaurs. Earth-Science Reviews 101, 68–100 A broad overview of all aspects of the Triassic and the origin of the dinosaurs.
Brusatte, S. L., Niedźwiedzki, G., and Butler, R. J. 2011. Footprints pull origin and diversification of dinosaur stem lineage deep into Early Triassic. Proceedings of the Royal Society B 278, 1107–13
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