Aliens...and Moral Valuing

Silliman's book seems to rely heavily on biology as
the solid backing, the facts, for his explored theories.
The discoursing pair touch upon the brain and
nervous system as being the points of reference when
noting non-human animals as being valuers and valued
beings in the incremental system. While I don't believe
that our Earthly knowledge has found conclusively
whether plant life is very sentient, or can feel pain (how
I cringe at that anti-vegetarian argument about a plant's
sense of pain), I find this focus on the brain to be limiting.

Not to totally jump into hypotheticals here, but I
would like to speculate that there is potential for
life in this universe, outside of what we know on Earth.
And as this hypothesis is somewhat of a likelihood,
it is important to recognize that different conditions
yield different bio-developments. What the brain
looks like, and functions as, on Earth may manifest
itself entirely differently in other beings.

Taking a wider look at the various ways life
(with greater levels of sentience) can develop is important
in that it gives us a more balanced perspective on the
life-as-we-know-it details on Earth.

If one can agree that different life-forms may have
different biological makeup, the they must (should) concede
that their point of agreement also submits that
other life-forms on Earth may follow this same trend.