Unmodern Synthesis: Developmental Hierarchies and the Origin of Phenotypes

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Unmodern Synthesis: Developmental Hierarchies and the Origin of Phenotypes

The question of whether the modern evolutionary synthesis requires an extension has recently become a topic of discussion, and a source of controversy.

We suggest that this debate is, for the most part, not about the modern synthesis at all.

Rather, it is about the extent to which genetic mechanisms can be regarded as the primary determinants of phenotypic characters.

The modern synthesis has been associated with the idea that phenotypes are the result of gene products, while supporters of the extended synthesis have suggested that environmental factors, along with processes such as epigenetic inheritance, and niche construction play an important role in character formation.

We argue that the methodology of the modern evolutionary synthesis has been enormously successful, but does not provide an accurate characterization of the origin of phenotypes.

For its part, the extended synthesis has yet to be transformed into a testable theory, and accordingly, has yielded few results.

We conclude by suggesting that the origin of phenotypes can only be understood by integrating findings from all levels of the organismal hierarchy.

In most cases, parts and processes from a single level fail to accurately explain the presence of a given phenotypic trait.

The debate between the proponents of the modern and extended syntheses is somewhat reminiscent of the duck-rabbit illusion. The two sides are probably talking about the same thing, but from different perspectives. If not, then we argue that the challenge is to do an experiment that rules out the alternative view.

The Extended (Evolutionary) Synthesis Debate: Where Science Meets Philosophy

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The Extended (Evolutionary) Synthesis Debate: Where Science Meets Philosophy

Recent debates between proponents of the modern evolutionary synthesis (the standard model in evolutionary biology) and those of a possible extended synthesis are a good example of the fascinating tangle among empirical, theoretical, and conceptual or philosophical matters that is the practice of evolutionary biology. In this essay, we briefly discuss two case studies from this debate, highlighting the relevance of philosophical thinking to evolutionary biologists in the hope of spurring further constructive cross-pollination between the two fields.

the question “Why are all phyla old?” resurfaces as a live empirical issue. If the number of thirty‐five or so animal phyla that are recognized today has remained stable since the Late Cambrian, this raises the question why such a large share of extant phyla arose during a short period and why so few have seen the light of day since.

a top‐down view of classification: taxa of higher rank evolved before taxa of lower rank originated [?]

the range of surviving phyla is unlikely to be explained by the extinction of intermediate forms

the sudden appearance of phyla is possibly related to the origin of distinctive regional patterning mechanisms

The debate about how the crown/stem group distinction should be related to the definition and delimitation of phyla continues, with different conceptions of phyla being preferred by different researchers

Continued assertions to this effect stand in the way of advancing genuine debates about the empirical and methodological constraints on what the study of development can tell us about macroevolution.

attributions of these three grades of typological thinking—[1]conceptual‐methodological, [2]logical, and [3]theoretical‐empirical—continue to feature in current debates about the nature and origins of phyla and phylum‐level body plans. However, while these attributions of typological thinking are meaningful as such, it is not always clear that they represent their contemporary targets accurately.