In the sentence extracted from biomedical literature, identify all the disease entities. The required answer format is the same sentence with HTML <span> tags to mark up specific entities. 
### Entity Markup Guides:
Use <span class="disease"> to denote a disease.

### Input Text: The conservation of the Rb1 gene in higher primates at the corresponding equivalent chromosome locus ( 14q14 ) of the human may serve as a phylogenetic marker to further trace the evolutionary pathway of human descent .
### Output Text:
The conservation of the Rb1 gene in higher primates at the corresponding equivalent chromosome locus ( 14q14 ) of the human may serve as a phylogenetic marker to further trace the evolutionary pathway of human descent . 