I would say the "plan" is for creation to awaken to itself and to God. How those species evolve towards that end simply follows that reach. What form it takes will be many and varied, some reaching higher than others, but none unnecessary.
Look at it this way. We humans will likely cease to exist as a species in the not-so-distant future, on a grand cosmological scale. Does this mean then end of that "plan" in creation? Oh no, not at all. The system created us, and I have no doubt at all other forms capable of 'knowing itself and God' have, do, and will continue to arise throughout the entire universe writ large, if not even here on this planet in ways we cannot know or see given our current arrogance.
Humans are a wonderful creation, "poised midway between the gods and the beasts," as Plotinus phrased it. But we assume in our arrogance, we are the highest evolved beings, in not only our biological abilities, but our mental and spiritual capacities. I think we have a long ways to go, to say the least, and "God's plan" to use that language, does not begin and end with us!
How much we create God in our own image to believe so!
It's it's God's nature to create, and all life is a reflection and expression of God. "The heavens declare the glory of God". "Consider the lilies of the field", etc. When will humans quit being arrogant about their position in the universe? I know? When they come face to face with God. Humility is the beginning of wisdom, and knowing God in the world and in ourselves.
The "only" children? Does it say that? What's more though, this story of ours about our origins as humans is a story we tell ourselves for various reasons, not the least of which is to speak about that very existential anxiety (angst), which causes humans to try to find God in all our substitutes, our projects, to know eternal life and avoid death. There are many deep layers to this story I'd love to discuss sometime, and I can tell you that it being about a scientific description of historical events, is definitely not one of them. This is not a compendium of God-knowledge on those pages, and a whopping big mistake to limit your understanding to them in that manner.
Oh, we're well on our way to doing just that right now in our arrogance, thinking we are the masters of our world. The sad joke will be on us, of course, or rather our children we are condemning.
What pray tell me in this entire universe is "not" God's creation? What?
And herein lies the crux of the existential anxiety. "We get away safe". No. We will all die. Everything is impermanent. It is only in resting in the timeless being of ourselves in God that the world may rise and fall, and we simply are. Eternal life is not after you die. Eternal life is now. And you either live within it, or out there somewhere in your anxieties, freaking ourselves out about death and dying and creating all manner of things to tell ourselves we will "get away safe". You don't get away, you simply open to what exists eternally now, within you, and you do so either by choice now, or by facing death then.