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Author Topic:   extended evolutionary synthesis (EES)
RAZD
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Message 1 of 2 (738505)
10-11-2014 12:10 PM


Does evolutionary theory need a rethink?
Nature | Comment
08 October 2014
quote:
Researchers are divided over what processes should be considered fundamental.
YES, URGENTLY Kevin Laland and colleagues
Does evolutionary theory need a rethink? Yes, urgently
Without an extended evolutionary framework, the theory neglects key processes, say Kevin Laland and colleagues.
... we have worked intensively to develop a broader framework, termed the extended evolutionary synthesis^1 (EES), and to flesh out its structure, assumptions and predictions. In essence, this synthesis maintains that important drivers of evolution, ones that cannot be reduced to genes, must be woven into the very fabric of evolutionary theory.
... We hold that organisms are constructed in development, not simply ‘programmed’ to develop by genes. Living things do not evolve to fit into pre-existing environments, but co-construct and coevolve with their environments, in the process changing the structure of ecosystems.
... standard evolutionary theory (SET) largely retains the same assumptions as the original modern synthesis, which continues to channel how people think about evolution.
The story that SET tells is simple: new variation arises through random genetic mutation; inheritance occurs through DNA; and natural selection is the sole cause of adaptation, the process by which organisms become well-suited to their environments. In this view, the complexity of biological development the changes that occur as an organism grows and ages are of secondary, even minor, importance.
Plasticity: commodore butterflies emerge with
different colours in dry (left) and wet seasons.
In our view, this ‘gene-centric’ focus fails to capture the full gamut of processes that direct evolution. Missing pieces include how physical development influences the generation of variation (developmental bias); how the environment directly shapes organisms’ traits (plasticity); how organisms modify environments (niche construction); and how organisms transmit more than genes across generations (extra-genetic inheritance). For SET, these phenomena are just outcomes of evolution. For the EES, they are also causes.
Valuable insight into the causes of adaptation and the appearance of new traits comes from the field of evolutionary developmental biology (‘evo-devo’). Some of its experimental findings are proving tricky to assimilate into SET. Particularly thorny is the observation that much variation is not random because developmental processes generate certain forms more readily than others^3. For example, among one group of centipedes, each of the more than 1,000 species has an odd number of leg-bearing segments, because of the mechanisms of segment development^3.
A more succinct hypothesis is that developmental bias and natural selection work together^4,5. Rather than selection being free to traverse across any physical possibility, it is guided along specific routes opened up by the processes of development^5,6.
Another kind of developmental bias occurs when individuals respond to their environment by changing their form a phenomenon called plasticity. For instance, leaf shape changes with soil water and chemistry. SET views this plasticity as merely fine-tuning, or even noise. The EES sees it as a plausible first step in adaptive evolution. ...
Mathematical models of evolutionary dynamics that incorporate extra-genetic inheritance make different predictions from those that do not^7—9. Inclusive models help to explain a wide range of puzzling phenomena, such as the rapid colonization of North America by the house finch, the adaptive potential of invasive plants with low genetic diversity, and how reproductive isolation is established.
... No longer a protest movement, the EES is now a credible framework inspiring useful work by bringing diverse researchers under one theoretical roof to effect conceptual change in evolutionary biology.
Sounds like Evo\Devo to me, being incorporated into a new synthesis theory, just as gene theory was previously incorporated in the "modern synthesis" and the development of SET (standard evolutionary theory).
quote:
NO, ALL IS WELL Gregory A. Wray, Hopi E. Hoekstra and colleagues
Does evolutionary theory need a rethink? No, all is well
Theory accommodates evidence through relentless synthesis, say Gregory A. Wray, Hopi E. Hoekstra and colleagues.
In October 1881, just six months before he died, Charles Darwin published his final book. The Formation of Vegetable Mould, Through the Actions of Worms^11 sold briskly: Darwin’s earlier publications had secured his reputation. He devoted an entire book to these humble creatures in part because they exemplify an interesting feedback process: earthworms are adapted to thrive in an environment that they modify through their own activities.
A profound shift in evolutionary thinking began during the 1920s, ... work between 1936 and 1947 culminated in the ‘modern synthesis’, which united Darwin’s concept of natural selection with the nascent field of genetics and, to a lesser extent, palaeontology and systematics. Most importantly, it laid the theoretical foundations for a quantitative and rigorous understanding of adaptation and speciation, two of the most fundamental evolutionary processes.
A worm cast pictured in
Charles Darwin’s final book.
Nonetheless there are evolutionary biologists ... who argue that theory has since ossified around genetic concepts. More specifically, they contend that four phenomena are important evolutionary processes: phenotypic plasticity, niche construction, inclusive inheritance and developmental bias. We could not agree more. We study them ourselves.
New words, old concepts
... all of these concepts date back to Darwin himself, as exemplified by his analysis of the feedback that occurred as earthworms became adapted to their life in soil. ...
Another process, phenotypic plasticity, has drawn considerable attention from evolutionary biologists. Countless cases in which the environment influences trait variation have been documented from the jaws of cichlid fishes that change shape when food sources alter, to leaf-mimicking insects that are brown if born in the dry season and green in the wet. ...
So, none of the phenomena championed by Laland and colleagues are neglected in evolutionary biology. Like all ideas, however, they need to prove their value in the marketplace of rigorous theory, empirical results and critical discussion. The prominence that these four phenomena command in the discourse of contemporary evolutionary theory reflects their proven explanatory power, not a lack of attention.
Modern expansion
Furthermore, the phenomena that interest Laland and colleagues are just four among many that offer promise for future advances in evolutionary biology. Most evolutionary biologists have a list of topics that they would like to see given more attention. Some would argue that epistasis complex interactions among genetic variants has long been under-appreciated. Others would advocate for cryptic genetic variation (mutations that affect only traits under specific genetic or environmental conditions). Still others would stress the importance of extinction, or adaptation to climate change, or the evolution of behaviour. The list goes on.
We could stop and argue about whether ‘enough’ attention is being paid to any of these. Or we could roll up our sleeves, get to work, and find out by laying the theoretical foundations and building a solid casebook of empirical studies. ...
Genes are central
Finally, diluting what Laland and colleagues deride as a ‘gene-centric’ view would de-emphasize the most powerfully predictive, broadly applicable and empirically validated component of evolutionary theory. Changes in the hereditary material are an essential part of adaptation and speciation. The precise genetic basis for countless adaptations has been documented in detail, ranging from antibiotic resistance in bacteria to camouflage coloration in deer mice, to lactose tolerance in humans.
Although genetic changes are required for adaptation, non-genetic processes can sometimes play a part in how organisms evolve. Laland and colleagues are correct that phenotypic plasticity, for instance, may contribute to the adaptedness of an individual. A seedling might bend towards brighter light, growing into a tree with a different shape from its siblings’. Many studies have shown that this kind of plasticity is beneficial, and that it can readily evolve if there is genetic variation in the response^14. This role for plasticity in evolutionary change is so well documented that there is no need for special advocacy.
Lack of evidence also makes it difficult to evaluate the role that developmental bias may have in the evolution (or lack of evolution) of adaptive traits. Developmental processes, based on features of the genome that may be specific to a particular group of organisms, certainly can influence the range of traits that natural selection can act on. However, what matters ultimately is not the extent of trait variation, nor even its precise mechanistic causes. What matters is the heritable differences in traits, especially those that bestow some selective advantage. Likewise, there is little evidence for the role of inherited epigenetic modification (part of what was termed ‘inclusive inheritance’) in adaptation: we know of no case in which a new trait has been shown to have a strictly epigenetic basis divorced from gene sequence. ...
All four phenomena that Laland and colleagues promote are ‘add-ons’ to the basic processes that produce evolutionary change: natural selection, drift, mutation, recombination and gene flow. None of these additions is essential for evolution, but they can alter the process under certain circumstances. For this reason they are eminently worthy of study.
We invite Laland and colleagues to join us in a more expansive extension, rather than imagining divisions that do not exist. We appreciate their ideas as an important part of what evolutionary theory might become in the future. We, too, want an extended evolutionary synthesis, but for us, these words are lowercase because this is how our field has always advanced^16.
In other words, the field of evolution is evolving as more information becomes available on the different processes involved, just as all sciences do, and that rather than just mutation and selection the processes involve:
  1. selection - survival and reproduction,
  2. genetic drift - stociastic effects,
  3. gene change by mutation and recombination,
  4. gene flow and population dynamics,
  5. phenotypic plasticity and response to environmental changes,
  6. niche (re)construction,
  7. inclusive inheritance or extra-genetic inheritance, such as evolution of behaviour, memes,
  8. developmental bias, how the way an organism evolves is related\confined by how it develops from egg to adult,
  9. epistasis complex interactions among genetic variants
  10. cryptic genetic variation (mutations that affect only traits under specific genetic or environmental conditions)
  11. extinction vs adaptation to ecological change, and the ability to adapt,
  12. etc.
To my mind many of these "add-on" processes involve the interaction of the organisms with their ecology, and this is really recognition that species cannot be talked about properly without including their ecologies.
Does this need to be updated?
The process of evolution involves changes in the composition of hereditary traits, and changes to the frequency of their distributions within breeding populations from generation to generation, in response to ecological challenges and opportunities.
And if so, how?
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Message 2 of 2 (738526)
10-11-2014 2:31 PM


Thread Copied to Biological Evolution Forum
Thread copied to the extended evolutionary synthesis (EES) thread in the Biological Evolution forum, this copy of the thread has been closed.

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