Instincts, Predators, and Animal Rights
Recently, I mentioned this to an animal rights vegetarian, and she said that there's an important difference between my cat and Jeffrey Dahmer - cats act on instinct, while humans have choices.
It would be a great argument, if it actually fit the facts. But it doesn't. It's wrong on both counts.
First, let's clarify what having instincts means. A lot of people, when they think of instinctive behavior, think of something like a songbird who, having never heard his species' song before, reproduces it perfectly upon adolescence. Or a duckling following the first thing he/she sees upon hatching.
Those are certainly instincts, but most instincts are more subtle. They're more on the level of certain connections being easier to learn, certain stimuli producing emotions that nudge you into certain actions, and so forth.
And it's mostly the more subtle instincts that humans have. Think of the most dangerous things a modern person is likely to encounter - cars and electricity. Most electrical outlets have several hundred times the amount of electrocity needed to kill us. And car accidents are one of the most common causes of accidental death. Yet the number of people who are afraid of cars or electricity is greatly outnumbered by the number of people who fear snakes or spiders. The simple reason is that we're genetically programmed to be more likely to fear spiders and snakes. Therefore, it takes a lot less to teach us to fear spiders and snakes than to fear electricity or cars, both things that cave men didn't have to worry about.
Sexuality is another example. It used to be that sex education was very poor, with many young couples marrying without either person knowing how babies are made. Yet they managed to make babies nonetheless - in fact, lack of sex education increases the likelihood of a teenager getting pregnant, instead of decreasing it. The reason? Sex is instinctive. You find yourself craving the touch of the other person, and the exact same sexual actions that are most pleasurable for the majority of people are also the ones most likely to cause pregnancy. The majority of people most enjoy heterosexual penis-in-vagina intercourse. Other activities may be fun, especially for a bit of variety, but standard intercourse, the only sexual activity that results in pregnancy, is also the most enjoyable one. Teens with no sex education will, by simple experimentation, end up figuring this out soon enough.
Language is another instinct. Attempts were made to explain language development in children by learning alone, but none of those theories could explain how good most children are at it - and the specific kinds of errors children make when learning, such as overregularization (eg 'haded'). The current theory is that children have an inborn 'language module' that leads them to expect a certain kind of structure to language, and they apply these rules to the specific language they're exposed to. If you look at all the languages in the world, they all have certain things in common, despite their vast differences. (Incidentally, children with specific language impairment seem to have genetically based abnormalities in the language module. One gene, FOXP2, has been found to be particularly important for learning how to do the rapid complex movements needed to say words.)
Another instinct is particularly relevant to the likes of Jeffrey Dahmer - instinctive morality. Children as young as 3 or 4, if asked, will tell you that some things are wrong only because an authority figure forbids them, and others are inherently wrong. The things that are inherently wrong are things that the children believe causes harm to other people. (These things can be justified by appealing to greater harm if they're not done, but that's another matter.) All cultures make this distinction, even if religious beliefs cause them to predict harm in different circumstances. And the only groups who don't draw this distinction are psychopaths and people with a specific kind of brain injury. Psychopathy, incidentally, seems to bear little relationship to the child's environment (abused kids are mostly normal on this particular test). Instead, psychopathy is genetic - for example, identical twins are much more similar on psychopathic personality traits than non-psychopaths. And though most psychopaths aren't serial killers, most serial killers are psychopaths.
So, though Jeffrey Dahmer did indeed have choices, his actions weren't simply a matter of choosing differently from most people. He most likely lacked certain instincts that strongly discourage the average person from doing the horrific acts that he did. On the other hand, one of the main reasons that I am not a serial killer is not a matter of what choices I've made, but the presence of certain instincts that make me feel horrified and disgusted at the thought of murdering in cold blood. It would take considerably more to push me into murder than it takes for a psychopath, and that's not something either of us have chosen. Instincts, or the lack of them, can have a considerable influence on a human's life - despite the common belief that we're above instincts.
And, conversely, cats can make choices, too. Certainly, attacking and killing rodents is largely instinctive (though it is affected by learning, since cats raised on mice hunt differently from cats raised on birds). But there are many cases of cats who befriend rodents. I had such a cat myself, a kitten named Hermes. The urge to attack his rat friends was clearly strong - he'd put his paws on them, lick them obsessively, and watch them with that 'predator focus' that cats have. But he never once hurt them, despite his instincts pushing him that way. He knew they were friends, and even though they were delicious, he must not eat them.
So, we're not really that different. Sure, our behavior is much less instinctive than cats, and we're much better at learning. But it's a difference of degree, not of kind. That argument may work with an insect, I don't know, but it certainly doesn't work with a cat.