“Human is a species” and “Every human is an animal” both feature the term human, but their judgments differ in target.
Human is a species: a logical classification of human nature as universal.
Every human is an animal: predication of animality of every human individual.
If the first were applied to individuals, “Zayd is a species” would follow, which is not intended. The second applies to every individual such as Zayd and Amr. That is the distinction between a nature considered in itself and the instances of that nature.