The Arboreal Theory
This theory argues that a change in diet from being insectivorous to herbivorous is the primary cause of the evolutionary shift in primates. Primates underwent dentition and limb morphology to better adapt to dietary changes and life in the trees. These arboreal mammals developed grasping hands with feet and nails which facilitated their flexibility and movement from tree branches ( Sussman, Rasmussen, & Raven, 2013). Another significant change was improved color vision to identify ripe fruit and to facilitate feeding.
Visual Predation Theory
Mart Cartmill originated this theory in 1992 arguing that adaptation of primates occurred because of the need to hunt prey in their complex arboreal habitats. As a result, achieving stereoscopic vision through orbital convergence was necessary. The stereoscopic vision was vital as it enabled primates to positively gauge distance and use grasping hands to capture insects at the ends of branches (Sussman, Rasmussen, & Raven, 2013).
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Angiosperm Radiation Theory
This theory attributes radiation of angiosperms (flowering plants) as the primary cause of primate evolution. An explosion and spread of flowering plants during the late Cretaceous period offered new opportunities and unexplored ecological niche to primates. Tasty and nutritious fruits that developed on terminal branches acted as food for primates. The primates, therefore, developed grasping hands to move from one treebranch to another searching for fruits. Stereoscopic vision enables them to see fruits clearly at low levels of light (Sussman, Rasmussen, & Raven, 2013).
New Discoveries on Evolution of Primates
New Discoveries do not discredit any of the theories in support of another. Discoveries only try to date the age of fossils found and how primate species differ. A new model presented in Zoologica Scripta argues that the distribution and diversification of primates are correlated with Mesozoic tectonic features. Michael Heads, a researcher of this model, claims that the prevailing theories are based on wide misrepresentations of fossil molecular clocks estimates. Heads explain that tectonic features like volcanic activities widely influenced the divergence of primates. However, the Angiosperm radiation theory best explains the diversification of primates. Ecological changes force animals to either evolve and adapt to a change in their environment or forever remain extinct.
Reference
Sussman, R. W., Rasmussen, D. T., & Raven, P. H. (2013). Rethinking primate origins again. American Journal of Primatology , 75 (2), 95-106.
