Walter Garstang: a retrospective

Abstract

Although, Walter Garstang died over 60 years ago, his work is still cited--sometimes praised, but sometimes belittled. On the negative side, he often appropriated ideas of others without attribution, ignored earlier studies conflicting with his theories, and clung to notions like inheritance of acquired characters, progressive evolution, and saltation after many of his contemporaries were advancing toward the modern synthesis. Moreover, his evolutionary scenarios--especially his derivation of vertebrates from a sessile ascidian--have not been well supported by recent work in developmental genetics and molecular phylogenetics. On the positive side, Garstang firmly established several points of view that remain useful in the age of evolutionary development (evo-devo). He popularized the valid idea that adaptive changes in larvae combined with shifts in developmental timing (heterochrony) could radically change adult morphology and provide an escape from overspecialization. Moreover, his re-statement of the biogenetic law is now widely accepted: namely, that recapitulation results when characters at one stage of development are required for the correct formation of other characters at subsequent stages (his stepping stone model). In other words, ontogeny creates phylogeny because some developmental features are constraints, favoring particular evolutionary outcomes while excluding others. This viewpoint is a useful basis for advancing concepts of homology and for comparing the phylogeny of ontogenies across a series of animals to ascertain the timing and the nature of the underlying ontogenetic changes.

The developmental hourglass model: a predictor of the basic body plan?

“…somite segmentation requires the prior establishment of the anteroposterior axis), strong conservation is inevitable (discussed further below). As Garstang proposed in his 'stepping-stone model' (Garstang, 1922;Holland, 2011), we often see that specific embryonic structures at one developmental stage require structures or developmental processes that arise or occur at an earlier stage. This type of dependency could have been a force that ensured conservation of embryonic structure.…”

The Paradox Of Portal Metastases In HCC Patients

“…The Amphioxus phylogeny from an advanced chordate was initially suggested by A.S. Romer in his hypothesis on the transition from "visceral" to "somatic" animals in evolution of the chordate (Romer and Parsons, 1986a;Romer, 1967;Romer, 1972Romer, , 1959. (Note: I do not think that the term "Garstang-Berrill-Romer hypothesis" (Holland, 2011;Lacalli, 2005) is correct, because Romer's model suggested origin of Amphioxus from advance motile chordate and not from a tadpole-like protochordates, as Lacally depicted (Lacalli, 2005). In my model, the yolk sac of the advanced chordate predecessor is suggested to be the homologous precursor of the Amphioxus hepatic diverticulum.…”

Homology in Amniote Brain Evolution: The Rise of Molecular Evidence

“…In these conditions, the concept of homology is an inference that depends on how one weights the comparative evidence, some scholars focusing on adult structure and others on embryology. Our perspective is that phylogeny is not a sequence of adult stages but a sequence of ontogenies, as proposed by the late Walter Garstang [Holland, 2011]. Thus, evolution will be ultimately understood only by unveiling the developmental transformations that took place in each lineage to yield the "endless forms most beautiful" [Darwin, 1859] of evolving life.…”