There are a few documented cases of well-trained monkeys who live with humans without causing harm, but in the vast majority of cases, it’s just too risky. Monkeys are essentially permanent toddlers who require full commitment from their human partners and must be constantly entertained or else they can become aggressive. They never grow up or mature, and a pet monkey who is ignored can quickly develop severe behavioral problems—or even die.
Most monkeys are found in the wild, and many are highly social animals that form troops consisting of several females with young and either one male (as in hamadryas baboons, mandrills, and most guenons) or several males (as in savannah baboons and langurs). Females have menstrual cycles and are sexually active throughout the year, although they often stop mating once they’ve reached maturity.
When a little monkey sees his mother pick up leaves and put them in her mouth, mirror neurons trigger the urge to do the same thing. And when he does, dopamine—a natural reward chemical—is released, and that feeling motivates him to do it again.
A monkey’s brain is wired to seek new experiences—that’s why they’re so curious, adventurous, and playful. But in some cases, monkeys are also trained to help with chores and everyday tasks like retrieving dropped items, turning pages of a book, scratching itches, pushing buttons and switches on remote controls or computers, and repositioning limbs on wheelchairs. These monkey helpers are known as companion primates, and they can be very beneficial to people with physical disabilities or Alzheimer’s disease, for example.