A juvenile Guanaco is Driven from its Herd

The guanaco are intelligent sociable animals, displaying traits like play and flirting. Like other ungulates (deer, goats, sheep, elk, etc), they typically roam in groups of either bachelor males or a single male with a harem of females. As juveniles go through puberty, they are driven out from the herd by the dominant male. I witnessed this, with the larger male chasing the younger, biting at its groin from behind in an attempted castration. Domesticated Llama also sometimes exhibit this behavior, which is why their front teeth are often removed. The mother then challenged the alpha, getting between them and angrily spitting at it. As harsh as this behavior is, it's evident how those who had that tendency would be more likely to amplify that trait into the gene pool of future generations by denying competitors the opportunity to mate, eventually becoming a characteristic of the entire population. This kind of aggressive behavior though only tends to become dominant in those patriarchal pack animals where the young don't require much support from the male to reach maturity. Newborns can begin to walk and graze shortly after birth.