Five jumbled up sentences (labelled 1, 2, 3, 4 and 5), related to a topic, are given below. Four of them can be put together to form a coherent paragraph. Identify the odd sentence and key in the number of that sentence as your answer.

1. No known real researcher of human behaviour would say that gender is all nature or all nurture.

2. The evidence for a biological basis for gender certainly doesn't mean we should be complacent in the face of sexism.

3. Many people are uncomfortable with the idea that gender is not purely a social construct.

4. Despite this empirical truth, researchers who study the biological basis of gender often face political pushback.

5. There's a political preference for gender to be only a reflection of social factors and so entirely malleable.