Statement:\nCrime is a function of the criminal's biological make-up and his family relations.\nConclusions:\nI. The incidence of crime is higher in identical twins than in fraternal twins.\nII. Families in which parents lack warmth and affection fail to build a moral conscience in the children.

Introduction / Context:
This is a classic statement–conclusion problem. The statement claims that criminal behavior is a function (i.e., influenced by) two broad factors: a person's biological make-up and family relations. From this, we must test what necessarily follows, without adding external research or assumptions beyond the words given.

Given Data / Assumptions:

• Crime is influenced by biological factors.
• Crime is influenced by family-relationship factors.
• No statistics, comparative studies, or specific sub-claims (e.g., about twins or parenting warmth) are asserted.

Concept / Approach:
In logical reasoning questions, a conclusion follows only if it is a necessary consequence of the given statement. Any new specificity (particular populations, measurements, causal thresholds) that is not explicitly stated cannot be treated as a necessary inference.

Step-by-Step Solution:
1) Test Conclusion I: “Higher crime in identical than fraternal twins.” This injects a specific comparative claim about twin concordance. The statement says nothing about twins (identical or fraternal), concordance rates, or heritability magnitudes; it merely says biology is one influence. Hence I does not necessarily follow.2) Test Conclusion II: “Parents lacking warmth fail to build conscience.” While family relations are mentioned, the statement does not single out warmth/affection, nor does it assert that a lack thereof necessarily results in failing to build conscience. It is a new, specific causation not contained in the general claim. II does not necessarily follow.

Verification / Alternative check:
If the statement had explicitly compared twin types or specified parental warmth as a necessary condition for conscience, the respective conclusions might follow. In the absence of such details, both are speculative.

Why Other Options Are Wrong:
“Only I” or “Only II” import details not stated. “Either I or II” still assumes at least one must follow, which is untrue. “Neither” correctly respects the generality of the premise.

Common Pitfalls:
Confusing “is a function of” with exact quantitative predictions; adding outside scientific knowledge to force a conclusion.

Final Answer:
if neither I nor II follow