plural adjectives?

[leisor]

I have doubts about the best way to express a "quality of many" in english. The following sentence start sounds good to me:
"Among human abilities..."

But, what if I want to start the sentence referring to one ability that belongs to all humans. Would it be OK to put like this?:
"Humans ability to..."
I know I could just say: "Human ability to..." but I'd like to know if it is correct to say it as the previous sentence.

Likewise, I have a list of symptoms for a sickness and every symptom has a scale of "seriousness". So if I want to say that there are various symptoms with a variety of expression, it would be OK for me to say: Symptoms severity?

Many thanks for your help

[Barb_D]

The human ability to -- says that this is an ability shared by [all] humans.

I would use "the severity of the symptoms" rather than "symptom severity."

Does this answer your questions?

[a writer, not a teacher]