An essential part of what makes us happy is seeing ourselves as healthy, natural creatures. We might have different conceptions of what "natural" means but our assessment of our own happiness - as well as our assessment of the happiness of others - is to a very large extent defined by our own definition of "natural". This is why it is so important to understand our place in the universe.
"For these reasons it will be useful for us to investigate nature: first, we shall leave behind what is sordid; next, we shall keep our mind, which needs to be elevated and great, separated from the body; next, when our critical faculty has been exercised on hidden matters, it will be no worse at dealing with visible ones. And nothing is more visible than these remedies which are learned in order to counter our wickedness and madness, things we condemn but do not forsake"
- Seneca, Naturales quaestiones 3.praef.18
"What will be the benefit?” you ask. The greatest possible benefit, the knowledge of nature. The investigation of this subject has many benefits, but none is finer than the fact that it captivates people with its own magnificence, and their motives for studying it are not gain but wonder"
- Seneca, Naturales quaestiones 6.4.2