Watson and Crick didn't propose a specific hypothesis for DNA replication. Their groundbreaking contribution was the discovery of the double helix structure of DNA in 1953. This discovery laid the foundation for understanding how DNA replicates, but the actual mechanism was not fully elucidated until later.

Here's why Watson and Crick couldn't have proposed a specific hypothesis for replication:

* Limited understanding of DNA's function: While they understood the structure, the precise function of DNA in terms of heredity and protein synthesis was still being unravelled.

* Lack of experimental evidence: The technology to study DNA replication at the molecular level was still in its infancy.

* Alternative models: At the time, other models for DNA replication existed, such as the dispersive model and the conservative model.

It was Matthew Meselson and Franklin Stahl who conducted the famous experiment in 1958 that provided the first strong evidence supporting the semi-conservative model of DNA replication. This model, now widely accepted, proposes that each new DNA molecule is composed of one original strand and one newly synthesized strand.

Therefore, while Watson and Crick's discovery of the double helix was crucial, the actual mechanism of DNA replication was not fully understood until later research.