Because it’s the difference in hormone levels compared to baseline that causes a high. While your first testosterone injection might cause a high, you will quickly get used to it.

Serotonin and dopamine are not just simply hormones that when released make you feel happiness. That’s a gross oversimplification.

There are a lot of ways to “cheat in happiness”, see any recreational drug.

One way to think about it is like artificial flavorings. The flavor of a cherry is complicated, so when a single chemical (usually benzaldehyde) is used to simulate the flavor of cherries or almonds, it’s a poor imitation of the real thing. It’s reminiscent of cherries because benzaldehyde is one of many flavor chemicals in cherries and almonds, but it doesn’t capture the full complexity of their flavor.

Similarly, a human experience like “winning” likely can’t be reduced to a single hormone or neurotransmitter. Brains and bodies are complex, so the experience of reward after winning likely includes many stimuli apart from testosterone - there are many subjective feelings and neurotransmitters/hormones involved in the struggle and victory, and these occur in a certain order during the experience of winning. The secretion of hormones and neurotransmitters is often local and has different effects in different parts of the body. Trying to achieve the same effect by injecting a single chemical is a bit like trying to swat a fly with a sledgehammer.

When the other cues of the struggle and victory are absent, it’s not surprising that even (a subset of) the same chemicals wouldn’t have the same effect. The brain’s expectations have a huge impact on our experience of events (consider the well-known placebo and nocebo effects), so even if we could perfectly simulate the hormonal effects of winning, a part of the subjective experience would be absent, so we might not expect the full effect to be present.

As for the god hypothesis… assuming one exists, he apparently has no problem with cheating, otherwise he wouldn’t have designed cuckoos to deposit their eggs in other birds’ nests so that they wouldn’t have to raise them on their own. Among thousands of examples where cheating occurs in nature and humans, often with impunity!

I can talk about your question on serotonin and dopamine (not so much testosterone).

Serotonin and dopamine are not "happy chemicals". That is a very common misunderstanding and a huge oversimplification. They are neurotransmitters with an enormous number of roles in the body, some of which are indirectly related to regulation of moods and emotions and most of which are not. But they do not, in and of themselves, cause "happiness" or feelings of reward. They're a means by which neurons communicate with eachother but they don't themselves carry information about what the message being communicated should be. Their actions are highly context dependent and depend on myriad other influences (neuroanatomical context, receptor type, modulating influence of other neurotransmitters...it's extremely complex). Trying to understand mood by looking at a neurotransmitter is a bit like trying to understand how a car works by studying the chemistry of the materials it is made from.

I kind of think of neurotransmitters sort of like sending messages in a large office. There might be several ways you can do that (email, written note, formal letter, telephone, face to face). Each method being analogous to a different neurotransmitter. Different methods may be more or less appropriate for different kinds of message but knowing the means of communication tells you nothing about the message itself. This is (very much simplified) the mistake people are making when they talk about serotonin and dopamine being "happy chemicals" and quote scientifically illiterate ideas like "dopamine hit".

We don't actually know how SSRI's work either. A lot of the "serotonin is a happy chemical" stuff actually comes from the observation that SSRIs do work, not the other way around. "SSRIs work therefore serotonin must improve mood". But there is growing evidence that their mechanism of action WRT depression may not be anything to do with serotonin at all. At least not directly. I mean they definitely do inhibit reuptake of serotonin but that is not necessarily how they are having their effect on mood.

This 2022 paper gives a good overview of where we're at with that stuff: https://www.nature.com/articles/s41380-022-01661-0

>The main areas of serotonin research provide no consistent evidence of there being an association between serotonin and depression, and no support for the hypothesis that depression is caused by lowered serotonin activity or concentrations.

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