Tuesday, June 05, 2018

On Desire 2018. Part 29: The Appetites

Here is where I begin to tell you the secret to losing weight.

There is a good reason for humans to evolve to be creatures whose desires fade or extinguish entirely upon being satisfied. After all, if they did not, then we would keep doing the same things until we died. Instead, it is better to eat until we are full, then to do something else. Get something to drink, perhaps. Have sex. Build a nest or burrow. Take care of the children. Sleep.

These are the desires that guide a simple animal's life. There isn't anything here that looks to means-ends rationality. Animals do not eat in order to survive - they eat in order to eat. They do not have sex in order to reproduce and perpetuate the species, they have sex in order to have sex. But they can't be doing any one of these things constantly. They must do one for a while - until they have satisfied that desire - and then move on to the next. If they should reach a state where all desires are satisfied, they lay in the shade under a tree and watch the world go by.

In the philosophy of desire, we are looking at the "death of desire principle", which Fredrico Laurie described as follows:

It appears that desire is incompatible with the representation that its content obtains. (Lauria, Frederico, (2017), “Guise of the Ought-to-Be” In Deonna J. & Lauria F. (eds). The Nature of Desire. Oxford University Press.)

We are, indeed, built so that the strength of a desire diminishes when satisfied. However, it has nothing to do with belief.

Take hunger for example.

There are two hormones associated with hunger.

Your stomach, when it is empty, produces ghrelin. Ghrelin produces hunger - it motivates you to eat. In the language that I have been using to describe the value-assignment theory of desire, ghrelin acts on the brain to assign a slowly increasing value to the proposition, "I am eating". When this value gets high enough, you fill your stomach, it produces less ghrelin, and your hunger subsides. Thus, we witness the death of desire. This death of desire may come with believing, "I am eating," but it is not the belief that "I am eating" obtains that kills hunger. It is the reduction of ghrelin in the bloodstream. As your stomach empties, it produces more ghrelin, and you get hunger again. Time for lunch!

If you eat too much, your body produces fat. Fat cells produce leptin. Leptin suppresses hunger. This keeps a person from getting too fat. It means that you can spend less time eating and more time working on other things . . . taking care of your children, building a shelter, quenching your thirst.

This is a simplistic description of these biological systems. As described, it seems that there would be no such thing as obesity. However, the biological systems motivating us to eat work a bit better than the biological systems suppressing our hunger. Also, there are maladies such as leptin resistance. The fat cells produce leptin, but the brain receptors do not receive it efficiently, meaning that the appetite is not suppressed as strongly as one would like. Taking a leptin pill will not help - the body is not reacting as it should.

Besides, your body likes to have a certain amount of leptin in your system. This is your leptin threshold. If it gets too low, you are motivated to eat - to produce more fat cells - to increase the leptin levels. Once the leptin levels get back up to what your body likes, then it will suppress your hunger again. But, what your brain wants in terms of leptin levels and what you want in terms of amount of fat and the leptin that amount of fat will produce may not be in agreement.

Something similar happens with sexual orgasm. At orgasm, the body produces prolactin, which diminishes sexual desire - at least for a time - particularly in men. The death of desire occurs because the body, in having realized a biological objective, takes steps to lower the value assigned to an act so that the agent can go on to do other things. This is a story for the death of some "desires that P" that has no need for a "belief that P obtains". Indeed, if a belief is all that is required, then there would be no need for these counter-systems to evolve.

This has a couple of important implications - other than what it has to say about the death of desire principle.

First, it suggests another distinction between beliefs and desires. It is important that the value assigned to the importance of proposition P being true changes over time. The importance of "I am eating" being true increases when the body needs food, and decreases when it has consumed the food it needs and then needs to work on other things. There is no similar reason for the value of the credence of a proposition to change over time.

Second, this reason for values to change is more applicable to positive desires than negative desires. By positive "desires that P" such as "that I am eating" or "that I am having sex". By negative desires I mean desires such as "that I am not in pain" or "that my child is not in danger." These aversions can stay perpetually high, motivating agents to avoid pain or danger to their child in everything else they may do.

I did say that I would tell you something about how to lose weight.

The short story is . . . research the biology of hunger. Find out how your body works. And make your plans based, not on folk stories and uninformed assumptions, but on the basis of science.

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