The chaos theory of evolution
18 October 2010 by Keith Bennett
Magazine issue 2782.
Evolution is chaotic (Image: Yehrin Tong)
Forget finding the laws of evolution. The history of life is just one damn thing after another
IN 1856, geologist Charles Lyell wrote to Charles Darwin with a question about fossils. Puzzled by types of mollusc that abruptly disappeared from the British fossil record, apparently in response to a glaciation, only to reappear 2 million years later completely unchanged, he asked of Darwin: "Be so good as to explain all this in your next letter." Darwin never did.
To this day Lyell's question has never received an adequate answer. I believe that is because there isn't one. Because of the way evolution works, it is impossible to predict how a given species will respond to environmental change.
That is not to say that evolution is random - far from it. But the neat concept of adaptation to the environment driven by natural selection, as envisaged by Darwin in On the Origin of Species and now a central feature of the theory of evolution, is too simplistic. Instead, evolution is chaotic.
Darwin's argument was two-fold: First, life evolves from common ancestors. Second, it evolves by means of natural selection and adaptation. The first part has been accepted as a basic premise of biology since 1859. The second is more controversial, but has come to be accepted over the past 150 years as the principal mechanism of evolution. This is what is known as "adaptationism".
Adaptationism certainly appears to hold true in microevolution - small-scale evolutionary change within species, such as changes in beak shape in Galapagos finches in response to available food sources.
However, there is still huge debate about the role of natural selection and adaptation in "macroevolution" - big evolutionary events such as changes in biodiversity over time, evolutionary radiations and, of course, the origin of species. Are these the cumulative outcome of the same processes that drive microevolution, or does macroevolution have its own distinct processes and patterns?
This is a long-running debate. In 1972, for example, Niles Eldredge and Stephen Jay Gould challenged the assumption that evolutionary change was continuous and gradual. Their "punctuated equilibrium" hypothesis argued that change happens in short bursts separated by long periods of stability, as distinct from the more continuous change over long periods expected to be the outcome of natural selection and adaptation.
Later, John Endler, an evolutionary biologist at the University of Exeter, UK, scrutinised claimed examples of natural selection but found a surprising lack of hard evidence (chronicled in his 1986 book Natural Selection in the Wild). More recently, and controversially, cognitive scientists Jerry Fodor of Rutgers University at New Brunswick, New Jersey, and Massimo Piattelli-Palmarini of the University of Arizona in Tucson have pointed out philosophical problems with the adaptationist argument (New Scientist, 6 February, p 28).
Palaeoecologists like me are now bringing a new perspective to the problem. If macroevolution really is an extrapolation of natural selection and adaptation, we would expect to see environmental change driving evolutionary change. Major climatic events such as ice ages ought to leave their imprint on life as species adapt to the new conditions. Is that what actually happens?
Our understanding of global environmental change is vastly more detailed than it was in Lyell and Darwin's time. James Zachos at the University of California, Santa Cruz, and colleagues, have shown that the Earth has been on a long-term cooling trend for the past 65 million years (Science, vol 292, p 686). Superimposed upon this are oscillations in climate every 20,000, 40,000 and 100,000 years caused by wobbles in the Earth's orbit.
Over the past 2 million years - the Quaternary period - these oscillations have increased in amplitude and global climate has lurched between periods of glaciation and warmer interglacials. The big question is, how did life respond to these climatic changes? In principle, three types of evolutionary response are possible: stasis, extinction, or evolutionary change. What do we actually see?
To answer that question we look to the fossil record. We now have good data covering the past 2 million years and excellent data on the past 20,000 years. We can also probe evolutionary history with the help of both modern and ancient DNA.
The highly detailed record of the past 20,000 years comes from analyses of fossilised tree pollen from lake and peat sediments. Tree pollen is generally recognisable to the level of genus, sometimes even species, and the sediments in which it is found can easily be radiocarbon dated.
In the 1970s and 1980s, palaeoecologist Margaret Davis at the University of Minnesota in Minneapolis created a map using this data which showed how North American tree taxa reached their respective present positions after the glaciers retreated at the end of the last ice age.
She found that the distribution shifts were individualistic, with huge variations between species in the rate, time and direction of spread. For example, larch spread from south-west to north-east, white pine from south-east to north-west. Rates vary from 100 metres a year to over 1000 metres (Annals of the Missouri Botanical Garden, vol 70, p 550). In other words, trees show no predictable response to climate change, and respond individually rather than as communities of species.
The fossil record also tells us that the make-up of modern forest communities differs from those of 20,000 years ago. Today we recognise various types of forest, such as boreal, deciduous and aspen parkland, each with a distinctive mix of tree species. Yet the fossil record tells us that these are just temporary groupings. Multi-species communities do not have long histories and do not shift their distributions in a coordinated way in response to climate changes, as Darwin supposed. We therefore cannot assume that the members of modern forest communities evolved together or are somehow dependent on each other.
The same appears to be true over longer timescales. Pollen data show that during earlier interglacial periods, when the climate was most similar to now, forest compositions were very different from today.
Research on animals has come to similarly unexpected conclusions, albeit based on sparser fossil records. For example, palaeontologist Russell Graham at Illinois State Museum has looked at North American mammals and palaeontologist Russell Coope at the University of Birmingham in the UK has examined insects (Annual Review of Ecology and Systematics, vol 10, p 247). Both studies show that most species remain unchanged for hundreds of thousands of years, perhaps longer, and across several ice ages. Species undergo major changes in distribution and abundance, but show no evolution of morphological characteristics despite major environmental changes.
That is not to say that major evolutionary change such as speciation doesn't happen. But recent "molecular clock" research suggests the link between speciation and environmental change is weak at best.
Die hard
Molecular clock approaches allow us to estimate when two closely related modern species split from a common ancestor by comparing their DNA. Most of this work has been carried out in birds, and shows that new species appear more or less continuously, regardless of the dramatic climatic oscillations of the Quaternary or the longer term cooling that preceded it (Trends in Ecology and Evolution, vol 20, p 57).
What of extinction? Of course, species have gone extinct during the past 20,000 years. However, almost all examples involve some degree of human activity, either directly (think dodos) or indirectly (large mammals at the end of the last ice age, 12,000 years ago).
In fact, we only know of one recent extinction with no human involvement - a species of spruce, Picea critchfieldii, which was common in the lower Mississippi valley at the height of the last ice age but died out 12,000 years ago (Proceedings of the National Academy of Sciences, vol 96, p 13847). Others undoubtedly occurred, but extinction appears to be a surprisingly rare response to substantial climatic changes (see diagram).
The overall picture is that the main response to major environmental changes is individualistic movement and changes in abundance, rather than extinction or speciation. In other words, the connection between environmental change and evolutionary change is weak, which is not what might have been expected from Darwin's hypothesis.
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Read more here/Leia mais aqui: New Scientist
Keith Bennett is professor of late-Quaternary environmental change at Queen's University Belfast, guest professor in palaeobiology at Uppsala University in Sweden, and author of Evolution and Ecology: The Pace of Life(Cambridge University Press). He holds a Royal Society Wolfson Research Merit Award
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NOTA CAUSTICANTE DESTE BLOGGER:
A nota tem a ver com a posição inadequada e inaceitável do MEC/SEMTEC/PNLEM com a aprovação da abordagem do fato, Fato, FATO da evolução em nossos livros didáticos de biologia do ensino médio com omissões, fraudes e distorções de evidências científicas.
O que é omitido aqui, é abordado ali por Bennett, um evolucionista. E é INTENCIONALMENTE OMITIDO dos nossos livros-texto. Por que? O nome disso é desonestidade acadêmica, carinhosamente chamada aqui de 171 EPISTÊMICO.
1. Ancestralidade comum. Bennett chama a ancestralidade comum de “premissa”: uma “premissa básica de biologia” que tem sido “aceita... desde 1859."
Bennett detona dois pilares teóricos do argumento de Darwin:
1. Ancestralidade comum. Bennett chama a ancestralidade comum de “premissa”: uma “premissa básica de biologia” que tem sido “aceita... desde 1859."
NOTA BENE: se é uma premissa, não é dedução e nem indução; não é predição nem descoberta. É apenas uma pressuposição – uma pressuposição inicial.
2. Seleção natural resultando em adaptação. Em seguida, Bennett detona a adaptação, dizendo que as mudanças climáticas (eu não pude resistir) que nós sabemos, não levaram à mudança macroevolucionária e, NOTA BENE, de nenhum jeito tipo lei previsível. As mudanças vistas no registro fossil são individualistas e inesperadas. Para complicar ainda mais o meio de campo de Down, a relação entre o genótipo e fenótipo de um organismo é não linear e caótico, e pode ter surgido sem nenhuma influência do ambiente.
Perguntas indiscretas deste blogger:
1. Se este é o status epistêmico da teoria da evolução através da seleção natural, então o que sobra para enshrine Darwinism como uma explicação científica válida? Aonde foi parar o fato, Fato, FATO da evolução? E por que continua sendo ensinado sem nenhuma abordagem crítica como fazem os cientistas???
2. Qual foi mesmo o maior fator na revolução científica moderna? Não foi a mudança do raciocínio dedutivo (da ideia de premissas de Aristóteles das formas na natureza alguém pode deduzir que...) para o raciocínio indutivo via método científico?
2. Seleção natural resultando em adaptação. Em seguida, Bennett detona a adaptação, dizendo que as mudanças climáticas (eu não pude resistir) que nós sabemos, não levaram à mudança macroevolucionária e, NOTA BENE, de nenhum jeito tipo lei previsível. As mudanças vistas no registro fossil são individualistas e inesperadas. Para complicar ainda mais o meio de campo de Down, a relação entre o genótipo e fenótipo de um organismo é não linear e caótico, e pode ter surgido sem nenhuma influência do ambiente.
Perguntas indiscretas deste blogger:
1. Se este é o status epistêmico da teoria da evolução através da seleção natural, então o que sobra para enshrine Darwinism como uma explicação científica válida? Aonde foi parar o fato, Fato, FATO da evolução? E por que continua sendo ensinado sem nenhuma abordagem crítica como fazem os cientistas???
2. Qual foi mesmo o maior fator na revolução científica moderna? Não foi a mudança do raciocínio dedutivo (da ideia de premissas de Aristóteles das formas na natureza alguém pode deduzir que...) para o raciocínio indutivo via método científico?
Ué, e considerar o ancestral comum como uma premissão não é retornar à lógica pré-científica como vemos na descrição do pensamento macroevolucionário?
Gente, até onde eu aprendi na universidade, é a matemática a ‘única’ciência onde o raciocínio dedutivo é apropriado.
Fui, nem sei por que 1, pensando que cada vez mais a fragilidade da teoria da evolução através da seleção natural e n mecanismos evolucionários (de A a Z), está mais que evidente. Só não vê quem esta fragilidade epistêmica quem não se submete às evidências, e a ciência é a submissão às evidências encontradas na natureza.
Gente, até onde eu aprendi na universidade, é a matemática a ‘única’ciência onde o raciocínio dedutivo é apropriado.
Fui, nem sei por que 1, pensando que cada vez mais a fragilidade da teoria da evolução através da seleção natural e n mecanismos evolucionários (de A a Z), está mais que evidente. Só não vê quem esta fragilidade epistêmica quem não se submete às evidências, e a ciência é a submissão às evidências encontradas na natureza.
Fui, nem sei por que, pensando 2: Exmo. Sr. Procurador da República que visita este blog, será que cabe um programa FICHA LIMPA de autores de livros didáticos? Chamar o MEC/SEMTEC/PNLEM para uma audiência pública para explicar esta situação danosa à formação acadêmica de nossos estudantes com uma abordagem omissa e fraudulenta como essa?
E a Teoria do Caos Evolucionário de Bennett ajuda ou embola ainda mais o meio-campo do time de Down???
E a Teoria do Caos Evolucionário de Bennett ajuda ou embola ainda mais o meio-campo do time de Down???
