After food, the greatest human need and human desire is meaning. Even more so than the ability to reason or even to speak, this is the great divide between human and animal. We share all other needs with the higher animal species and share many needs with some of the lower animal species. Like them, we need food, shelter and companionship. But, while human beings seek and need meaning more than anything except food (and companionship — but for human beings, companionship usually provides some meaning, and sometimes enough), no animal needs or seeks meaning.
— Dennis Prager in The Question That Explains Almost Everything
Nozomi is about as domesticated as a dog can get. She spends 23 hours of every day inside a house built for humans and she sleeps at least 16 of those hours. When she's awake and moving about, she's doing so mostly out of curiosity and in search of attention. Both of these are valid reasons to be surveying the house, but neither can offer any sense of meaning.
The same can be said about the boy despite his superior cognitive abilities over Nozomi. He has a greater degree of freedom and far more options to choose from, but he does not yet seek nor need meaning in his life. This fundamental motivation will begin to manifest in a couple of years as he continues to explore the world and discover his interests.
For many adults, however, meaning means a great deal. It's part of the answer to the ultimate question: Why am I here?1
On days when I'm feeling particularly depressed, I try to think of an additional answer to the question of why I exist. There are the obvious reasons, like "I am here to be a good father and role model to my son" and "I am here to be a good companion and friend for my wife". These are strong, valid reasons to exist. But is there more that a person could be doing?
Of course there is.
For a great deal of my adult life I thought the reason for existence was to help solve difficult problems through the use of software, as it's really the only skill I possess that is even remotely marketable. This was probably true for a time but, as I continue to progress into middle age, it seems silly to tie a personal meaning to a corporate expectation. Yes, I can certainly continue to work with software to solve problems, help people, and pay the bills … but this isn't something that should provide meaning. Work as meaning is a shallow substitute for something that can be meaningful.
This year I'll pass the midway point of my expected lifespan. Over the last 40-odd years I've found meaning with all sorts of relationships, activities, and endeavours. Some have been shallow and some have been more worthwhile than anything else. But as I think about the next four decades, I'd like to continue finding meaning in new ways with new people and new objectives. Hopefully by doing this, I'll have the opportunity to look back on my life and see that it wasn't completely consumed by career ambitions. There's a lot more to life than work, after all.
The biological answer to this question is irrelevant. Anyone self aware enough to ask the question with any sort of seriousness understands they exist because their ancestors have successfully procreated for countless generations.