Grit and consequence

Abstract

Grit is implicated in several biological phenomena—it wears teeth, it fractures teeth, it drives tooth evolution, it elicits complex manual manipulations—any one of which could be described as a central topic in evolutionary anthropology. But what is grit? We hardly know because we tend to privilege the consequences of grit (it is abrasive) over its formal features, all but ignoring crucial variables such as mineral composition, material properties, and particle geometry (size, angularity), not to mention natural variation in the habitats of primates and their food surfaces. Few topics have animated so much debate and invited such cool indifference at the same time. Our goal here is to shine a light on grit, to put a philosophical lens on the nature of our discourse, and to call attention to large empirical voids that should be filled and folded into our understanding of primate natural history and evolution.

Tooth chipping patterns in Archaeolemur provide insight into diet and behavior

“…Environmental “grit” comes in a variety of forms. Little is known about how animals prevent or minimize ingesting and masticating these small hard particles (Fannin et al, 2021 ).…”

Macrowear effects of external quartz abrasives of different size and concentration in rabbits (Oryctolagus cuniculus)

“…Even though tooth wear was lower on the fine silt diet compared to the coarse sand, the silt still caused significant tooth height differences compared to the control diet (Table 3 ), suggesting that the polishing effect also includes dental tissue removal. In a natural environment, fine silt can be transported by wind onto plants in the dry season (Fannin et al, 2021 ; Kok et al, 2012 ), while larger particles only end up on leaves when they are propelled from the ground upwards by the splash of rain drops (Sanson et al, 2017 ) during the rainy season. Shorter hypselodont teeth could thus reflect a sandy environment with low grass coverage during the rainy season, rather than a windy dry season.…”

“…A p a r tf r o md i r e c tt o o t h -to-tooth contact during mastication, major causative agents for macroscopic tooth wear are the silicates inside plant material (endogenous phytoliths) (Martin et al, 2019;Müller et al, 2014) as well as plant-external quartz silica in the form of dust or grit trapped on plant leaves due to wind and rain (Fannin et al, 2021;Madden, 2015;Sanson et al, 2017). The abrasive potential of internal and external a b r a s i v e si sd e p e n d e n to ns e v e r a lp h y sical characteristics such as size, shape, and hardness (Lucas et al, 2013)i nc o m p a r i s o nw i t ht h ea f f e c t e d dental tissues (Kaiser et al, 2018)a sw e l la st h e i ro v e r a l lc o n c e n t r a t i o n and distribution in the diet.…”

Differentiating siliceous particulate matter in the diets of mammalian herbivores

“…Ecologists use the term silica because Si is always associated with oxygen (SiO 2 ) in ecosystems, where it forms an essential component of the biogeochemical cycle (Cooke & Leishman, 2011; Vandevenne et al, 2013)—indeed, every vascular plant incorporates silica for a wide range of reasons (Epstein, 1994; Strömberg et al, 2016); e.g., stress from shifts in local abiotic conditions, such as low atmospheric CO 2 , heat or drought (Strömberg et al, 2016), or to defend against biotic threats such as microscopic pathogens (Fauteux et al, 2005), animal herbivores (Massey et al, 2007; McNaughton et al, 1985), or both (Cooke & Leishman, 2011). Paleobiologists, in turn, have focused their attention on silica when debating the evolutionary consequences of chewing it, with a special emphasis on the dental adaptations of mammalian herbivores (Damuth & Janis, 2011; Fannin et al, 2021; Kaiser et al, 2018; Madden, 2014).…”

“…For paleobiologists, there is a crucial material difference between the endogenous silica bodies of plants (opaline phytoliths) and exogenous ‘grit’, a term with dual meaning. Grit can describe heterogeneous mixes of particles, but many authors use it as a synonym for crystalline quartz, a major component of soil, sand, and ash, as well as aerosolized atmospheric dust (Fannin et al, 2021; Glaccum & Prospero, 1980; Perlwitz et al, 2015). Chewing plant foods exposes teeth to phytoliths and grit (i.e., quartz), and it is this inextricable mix of siliceous particles that underlies decades of spirited debate.…”