Both the Australian marsupial bilby and the North American placental jack rabbit are found in hot, dry environments - HSC - SSCE Biology - Question 21 - 2008 - Paper 1

The Darwin/Wallace theory of evolution primarily relies on the principles of natural selection. In environments characterized by heat, such as the habitats of both the marsupial bilby and the jack rabbit, having larger ears can confer certain advantages.

Firstly, larger ear sizes may facilitate increased heat dissipation. This adaptation helps both species manage their body temperature more effectively in hot climates. According to the principle of survival of the fittest, individuals with traits that enhance their ability to adapt to their environment tend to reproduce more successfully.

Moreover, these organisms may have evolved similar ear sizes due to convergent evolution—a phenomenon where different species develop similar traits independently to adapt to similar environmental pressures. It's important to emphasize that this is not a case of Lamarckian evolution, where traits acquired during an individual's lifetime are passed on to offspring. Instead, the trait of ear size is a result of natural selection acting on heritable variations that existed within the populations.

In summary, the similarity in ear size between the bilby and jack rabbit can be attributed to the adaptive advantages of larger ears in hot, dry environments, supported by the mechanisms laid out by the Darwin/Wallace theory of evolution.