User:Jtwsaddress42/Projects/Project 2/Sections/Chapter 12/From Phagocytosis To Gastric Provisioning - The Evolution Of Cellular Individuality Within The Somatic Population

Although the popular Darwininistic recapitulist interpretations of embryology championed by Ernst Haeckel dominated the discussion of biological origins at the time, there were dissenters of all kinds. But within the realm of those committed to a scientific and biological explanatory theory of animal origins, Elie Metchinikoff was a prominent dissenter. Mechanistic continuity and physiological viability are the necessary requirements Metchnikoff demanded of each stage of an embryological and evolutionary transition. Metchinikoff challenged the orthodoxy of Haeckels Gastraea theory of animal origins on the basis that it was not mechanistically continuous and physiologically viable in all its intermediate stages between unicellularity and multicellularity. He argued that there must have been a preceding historical period leading to the extracellularly-digesting "gastraea" - and, that was the colonial ancestors of the mesoderm-derived lmyphocytes which exhibit the ancestral mode of intracellular digestion through phagocytosis - Phagocytella.

In an attempt to explain what was required to make the transition from individual intracellularly-digesting phagocytic choanoflagellate cells to organized and differentially specialized tissues reliant on extracellular digestion and nutritional provisioning, Cavalier-smith proposed that "Epithelia and connective tissue could evolve only by compensating for dramatically lower feeding efficiency that differentiation into non-choanocytes entails. Consequentially, larger bodies enabled filtering more water for bacterial food and harbouring photosynthetic bacteria, together adding more food than cell differentiation sacrificed."

This requirement for mutual nutrient provisioning is the necessary pre-condition for beginning the pathway to cellular specialization within the multicellular population. Some cells will forgo the essential task of harvesting food to specialize, in return their services will be rewarded by other cells becoming super harvesters which will provision the specialized non-digestive cells with their nutritive needs. Resource provisioning pathways are fundamental to multicellular organization, but the specialized cells within animals are critically dependent upon them.