Fig. 3

Force-dynamic models of evolutionary reasoning. Generalized representations of force-dynamic reasoning are exhibited when the presence (a) or absence (c) of a force causes a change in the state of the object. When a force is present, it causes the ball to roll up the ramp, against its intrinsic tendency (being at rest). In the absence of a the force (c), the ball is no longer being pushed up or held on the ramp and so returns to its intrinsic state as it rolls down the ramp. This reasoning can be applied to evolutionary examples such as that shown in the gain (b) and loss (d) of a trait. In trait gain (b), the force is the pressure that causes the development of thorns on roses, whereas in trait loss (d), the absence of said pressure causes the loss of the trait (thorns)