HABITAT HETEROGENEITY IN NON-MARINE SETTINGS AS A PROMOTER OF EVOLUTIONARY NOVELTY

The de novo origin of biological form is tied to many of the major evolutionary transitions in biology, including the origins of complex multicellularity in animals and plants, the origin of the nucleus in the eukaryotic cell, and to the origin of the first prokaryotic cell from ancestral protobionts. Physiochemical parameters that characterize non-marine paleoenvironments might have acted as direct causal agents in morphogenic and biochemical changes to growing organisms, and, as such, would have played a role in the origination of novel characters in evolving lineages of organisms. For example the origin of cell wall heteropolymers may have first occurred in response to dehydration synthesis reactions occurring in periodically desiccating environments. This mechanism may have led to the evolution of rigid cell walls that characterize many algae, along with all plants and fungi. A second example is tissue-level differentiation that occurs in an early multicellular protist of probable holozoan affinity. This fossil case study follows very closely the Differential Adhesion Hypothesis (DAH), which was originally formulated by Malcolm Steinberg as an explanation of how physical forces may have played a role in the evolution of animal development. A third example involves the origin of cadherin based cell-cell adhesion in settings with enhanced levels of Ca²⁺, that is inferred from authigenic mineralization of phosphate in billion-year old lacustrine settings.

While these examples do not explain exactly how physiochemically-induced biotic responses to environmental parameters at the cellular level become fully incorporated into life-cycle and developmental signaling pathways that are specified in a genome, they do provide the basis for some attractive hypotheses for physically-induced morphogenesis as a means to generate de novo characters in evolving lineages in non-marine settings. And, as such, they are a step in the direction of understanding how secular environmental change in non-marine settings may have contributed to evolutionary diversification, not through Natural Selection, but instead through novel character generation.