The camelid lineage has a good fossil record. Camel-like animals have been traced from the thoroughly differentiated, modern species back through early Miocene forms. Their characteristics became more general, and they lost those that distinguished them as camelids; hence, they were classified as ancestral artiodactyls.[citation needed] No fossils of these earlier forms have been found in the Old World, indicating that North America was the original home of camelids, and that Old World camels crossed over via the Bering Land Bridge. The formation of the Isthmus of Panama three million years ago allowed camelids to spread to South America as part of the Great American Interchange, where they evolved further. Meanwhile, North American camelids died out at the end of the Pleistocene.

One of the main uses for llamas at the time of the Spanish conquest was to bring down ore from the mines in the mountains. Gregory de Bolivar estimated that in his day, as many as 300,000 were employed in the transport of produce from the Potosí mines alone, but since the introduction of horses, mules, and donkeys, the importance of the llama as a beast of burden has greatly diminished.

The most-noticeable difference between the two animals is their sizes. Alpacas are smaller, around 90 cm (35 inches) high at the shoulder and between 55 and 65 kg (121 to 143 pounds). Llamas are the biggest lamoid at about 120 cm (47 inches) at the shoulder and about 113 kg (250 pounds). So llamas are going to be a lot bigger than their cousins. Their faces are also dissimilar: alpacas have small, blunt faces with short ears, while llamas have more-elongated faces with banana-sized ears.

The gestation period of a llama is 11.5 months (350 days). Dams (female llamas) do not lick off their babies, as they have an attached tongue that does not reach outside of the mouth more than half an inch (1.3 cm). Rather, they will nuzzle and hum to their newborns.

An "orgle" is the mating sound of a llama or alpaca, made by the sexually aroused male. The sound is reminiscent of gargling, but with a more forceful, buzzing edge. Males begin the sound when they become aroused and continue throughout the act of procreation – from 15 minutes to more than an hour.

While the social structure might always be changing, they live as a family and they do take care of each other. If one notices a strange noise or feels threatened, a warning bray is sent out and all others become alert. They will often hum to each other as a form of communication.

The question is complicated by the circumstance of the great majority of individuals that have come under observation being either in a completely or partially domesticated state. Many are also descended from ancestors that have previously been domesticated, a state that tends to produce a certain amount of variation from the original type. The four forms commonly distinguished by the inhabitants of South America are recognized as distinct species, though with difficulties in defining their distinctive characteristics.