Can Randomness and Chance cause the natural evolution of life?
For that matter, can randomness and chance cause anything?
This common banner of Creationists promoting 'Intelligent Design' and claiming natural evolution cannot happen because of randomness and chance in natural events. Is the variation in the outcomes of cause and effects truly random?
What is the relationship between cause and effect and the variation in the outcomes in nature. Can we have the complexity of life we have today evolve from simplicity?
What are the known causes of life and evolution?
Does random and chance occur in nature? If so how?
First reference:
The chaos theory of evolution By Keith Bennett
Forget finding the laws of evolution. The history of life is just one damn thing after another
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.
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?
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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.
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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).
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If environmental changes as substantial as continent-wide glaciations do not force evolutionary change, then what does? It is hard to see how adaptation by natural selection during lesser changes might then accumulate and lead to macroevolution.
I suggest that the true source of macroevolutionary change lies in the non-linear, or chaotic, dynamics of the relationship between genotype and phenotype – the actual organism and all its traits. The relationship is non-linear because phenotype, or set of observable characteristics, is determined by a complex interplay between an organism’s genes – tens of thousands of them, all influencing one another’s behaviour – and its environment.
Not only is the relationship non-linear, it also changes all the time. Mutations occur continually, without external influence, and can be passed on to the next generation. A change of a single base of an organism’s DNA might have no consequence, because that section of DNA still codes for the same amino acid. Alternatively, it might cause a significant change in the offspring’s physiology or morphology, or it might even be fatal. In other words, a single small change can have far-reaching and unpredictable effects – the hallmark of a non-linear system.
Iterating these unpredictable changes over hundreds or thousands of generations will inevitably lead to evolutionary changes in addition to any that come about by the preferential survival of certain phenotypes. It follows that macroevolution may, over the longer-term, be driven largely by internally generated genetic change, not adaptation to a changing environment.
The evolution of life has many characteristics that are typical of non-linear systems. First, it is deterministic: changes in one part of the system, such as the mutation of a DNA base, directly cause other changes. However, the change is unpredictable. Just like the weather, changes are inexorable but can only be followed with the benefit of hindsight.
Second, behaviour of the system is sensitive to initial conditions. We see this in responses to glaciations in the Quaternary period. The exact circumstances of the beginning of each interglacial determine the development of the whole period, leading to unpredictable differences between interglacials (
Quaternary Science Reviews, vol 14, p 967).
Third, the history of life is fractal. Take away the labelling from any portion of the tree of life and we cannot tell at which scale we are looking
(see diagram). This self-similarity also indicates that evolutionary change is a process of continual splitting of the branches of the tree.
Fourth, we cannot rewind, as Stephen Jay Gould argued in
Wonderful Life. Were we to turn the evolutionary clock back to any point in the past, and let it run again, the outcome would be different. As in weather systems, the initial conditions can never be specified to sufficient precision to prevent divergence of subsequent trajectories.
Life on Earth is always unique, changing, and unpredictable. Even if certain patterns can be dimly discerned, our ability to do so diminishes with time, exactly as for the weather. Consider any moment of the geological record of life on Earth: to what extent were the changes of the next 10 or 100 million years predictable at that time? With the benefit of hindsight, we might be able to understand what happened, and construct a plausible narrative for those events, but we have no foresight.
This view of life leads to certain consequences. Macroevolution is not the simple accumulation of microevolutionary changes but has its own processes and patterns. There can be no “laws” of evolution. We may be able to reconstruct the sequence of events leading to the evolution of any given species or group after the fact, but we will not be able to generalise from these to other sequences of events. From a practical point of view, this means we will be unable to predict how species will respond to projected climate changes over next century.
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We still have much to learn about how life evolved but we will not develop a full appreciation until we accept the complexity of the system."
