A story that says that values are real-world entities that are open to scientific investigation has to say something about what values are and how values came to exist. It is a story about how moral values themselves came to take form and grow out of a sea of general values.
Desirism has a story to tell here. It is a story compatible with the view in general, and moral-value in specific, is not to be found exclusively in some amorphous concept of "well-being".
Value exists as a relationship between states of affairs and desires. Moral value exists as relationships between malleable desires and other desires. The story of how value in general, and moral value in specific, came to exist is the story about how desires in general, and malleable desires in specific, came to exist.
Beliefs and desires came to exist when brains came to exist. Neural nets became complex enough that the entity with this net could devote a part of it to creating a (necessarily imprecise) model of the external world - a set of 'beliefs'. It acquired the ability to run simulations of this model to test the probable outcome of various actions, and then to choose those outcomes that had the best outcome.
Of course, this required the ability to assign values to potential outcomes - to states of affairs - which is where desires entered the picture.
This model gives us beliefs and desires as propositional attitudes that aim to correspond to facts about the external world. Beliefs refer to the model itself - what it says about how the real world is. Desires are used to evaluate the outcomes of mental simulations. This simulate-and-evaluate system gives the creature an ability to choose among different possible intentional actions. Note that it does so without requiring the possibility of contra-causal free-will.
Once we have desires, we have relationships between states of affairs in desires. That is to say, we have value.
The desires that early creatures acquired had nothing to do with well-being. If a particular desire contributed to well-being, this was a side-effect, or an unintended consequence of how the system worked.
We cannot even argue that evolution, over time, would favor desires that contribute to well-being and shun desires that avoid well-being. There would be some tendency along these lines. However, the driving force of evolution is to create an entity that chooses actions that results in genetic replication. This will lead to choosing the action that contributes to the agent's well-being when it is useful for genetic replication, but to choose actions that are contrary to individual well-being when that promotes genetic replication.
Animals do not have sex because they seek to have offspring and to reproduce the species. This is the effect of those actions. However, animals are brought to engage in these actions by means of a desire for sex, not by means as a desire for reproduction. This is why we, as humans, have a desire for sex, and not (or not so much) a desire for reproduction.
We also have a desire to eat. We do not have a desire to maintain our health through the consumption of calories. We have a desire for the consumption of calories. Our food tastes - our desires for particular types of food - are desires for those foods that tended to keep our biological ancestors alive. Our environment has since changed. We have changed it. However, some of our desires - our desire for food - are still more fit for that older environment than for the environment that we have now.
How did desires become malleable?
Well, let us start with beliefs.
Hard-wiring beliefs into a system has some drawbacks. The most important of these is that individual creatures will find themselves in different environments. It would be useful for the creature to have a way of discovering truths about this environment and changing its mental model accordingly. Furthermore, environments change. If one fixes a set of beliefs about an environment, and the environment changes, then the model that the creature is using to evaluate intentional actions is going to fail. It is better to have a mental model where, if the environment changes, the model changes, and the creature retains the ability to use the model to choose intentional actions.
It is useful to have desires be somewhat malleable in some instances as well. This is because assigning a particularly high value to a particular state may be useful in one environment, but not useful if the environment changes. The eating of toads may be useful if toads represent calories and protein. Yet, a creature's taste in toads may not fit it for an environment in which toads are poisonous.
One good bout of sickness should be enough for a creature to acquire an aversion to eating a particular type of toad. Acquiring the aversion is far more efficient than acquiring and maintaining a memory that eating the type of toad in question caused illness when young associated with the desire to avoid illness. It's simply more efficient to learn an aversion to eating a particular type of toad.
Besides, beliefs and desires are both housed in the same brain. If we allow the brain to be modifiable by interaction with the environment so that a creature learn new beliefs, then we have a plastic brain that can also be used to learn new desires.
So, now, a creature finds itself in an environment where it is surrounded by other creatures that have malleable desires. Some of those creatures are creatures that it interacts with repeatedly. In other words, an entity with the ability to modify its environment so as to fulfill its desires finds that the environment contains entities with malleable desires. The next leap in the development of morality is one in which the modification of the environment takes the form of modifying the malleable desires of others. Using the mechanisms by which desires are acquired, one arranges for others to have experiences that will cause the learning of desires that one finds useful.
Desires are learned by their relationships with positive and negative experiences - the way a bout of illness created an aversion to eating a particular type of toad. Positive and negative experiences - praise, condemnation, reward, and punishment - are readily available tools for modifying the desires of others.
These are also tools available to others for modifying the desires in oneself. While the creature is teaching others to have desires that are useful to him, he is being taught the desires that are useful for others. The next loop in the spiral is that in teaching others to have desires that are useful to him, he is teaching others to have desires that are useful for the fulfillment of his own desires which, in turn, are desires that are useful to others. And so it goes, until a moral system emerges.
So, the person who is molding the desires of others to promote desires that tend to fulfill his desires, will come to be molding desires that others have made into desires that tend to fulfill their desires. The person make kind and honest by social conditioning will find himself using praise and condemnation to mold the desires of others so as to fulfill his own desires for kindness and honesty.
So, here we have a story concerning the rise of morality. It is a story that fits very well into the fact that humans evolved. It is a theory that does not postulate anything other than desires as reasons for action that exist in the real world. It does not require a god. Nor does it postulate any type of intrinsic values, social contracts, hypothetical imperatives, impartial observers, committees making decisins behind a veil of ignorance, or any of the other conventionial fictions that are found in other stories. For the record, it also does not require evolved moral sentiments, nor does it give any weight to moral intuitions.
It is a story that explains why praise and condemnation are such an integral part of moral practices - a feature of morality that other stories simply ignore as if it needs no explaining.
Yet, it is a story that finds moral value in desires that tend to fulfill other desires.