Moral theories and statements that involve references to nature, or more precisely references to biological facts in the context of human valuing and/or normativity, face significant objections. Perhaps the most popular one is the “is-ought” problem: the question of whether norms (and values) can be derived from facts. The problem can also be referred to as the problem of the relation between facts, values and norms. This thesis examines this relation by proposing a differentiation between ontological and epistemological perspectives of the problem. On the one hand, such approach reflects and acknowledges points about differences between biological facts and values (and norms) that lead some authors to object to such references. The analysis of the is-ought problem, as means of addressing the epistemological perspective of the fact-value problem, leads to the conclusion that a valid derivation of a norm from a fact requires an appropriate justification by reasons and/or values. On the other hand, the approach involves inquiring into what urges philosophers to make references to nature by investigating parallels between biology and human valuing. This inquiry is understood as an inquiry into the ontological aspect of the problem. Empirical evidence that demonstrates our embedment in nature, as frequently cited by philosophers such as Philippa Foot or Michael Ruse, is discussed and interpreted clearly delineating its descriptive and normative statements, thus interpreting its relevance to evaluative and normative exercises. The understanding of references to biological facts in valuing and normative exercises is further discussed in the light of discussing both the parallels and the differentiation between purposeful understanding of human decision-making and biology. Finally, the developed understanding of values` relation to facts is applied the understanding of values as subjective and objective.