Lathyrism, a debilitating neurological disorder caused by the consumption of the legume Lathyrus sativus, is widespread among the domestic animals of some countries. Attempts to use rats to study lathyrism have generally failed. Rats that ingested Lathyrus sativus did not produce the symptoms associated with the disorder. Which one of the following is most strongly supported by the information above? ['Laboratory conditions are not conducive to the development of lathyrism.', 'The physiology of rats is radically different from that of domestic animals.', 'The rats did not consume as much Lathyrus sativus as did the domestic animals that contracted lathyrism.', 'Not all animal species are equally susceptible to lathyrism.']