Advanced robotic hand prostheses are praised for their impressive robust and fine grasping capabilities generated from intricate systems. Nevertheless, a high demand remains for grasping mechanisms that are mechanically simple, lightweight, and cheap to produce, easy to assemble and low in maintenance costs. This paper presents the design of a partially compliant underactuated finger to demonstrate the feasibility of achieving these rigorous requirements. The conceptual topology of the three phalanx finger is selected based on competitive analysis. Employing Pseudo-Rigid Body Model and Finite Element Analysis, a genetic optimization problem is formulated to minimize bending stresses within compliant flexures. The result is a fully functional demonstrator capable of flexing 180o in finger rotation. The prototype is fabricated from flexible high strength nylon and requires no assembly steps beyond 3D printing. Experimental testing verifies the design method with an acceptable error of