From a more reliable source:
In the course of the approximately 5,700 tests conducted by the researchers, they found that for 22 of the 56 gene pairs studies, the paralogous gene took over in the absence of its counterpart. “Gene function is maintained by the paralogous gene still present in the cell, which supports the hypothesis that genetic duplication ensures genome resilience,” said Christian Landry. However, for 22 other pairs, the absence of one of the two paralogous genes interfered with cellular function. “The presence of both paralogous genes from the pair is sometimes essential to maintain cellular function,” he explained. In these cases, the spontaneous mutation of one of the paralogous genes would be sufficient to create a situation where gene function is no longer assured. Duplication of the gene therefore made the genome more fragile.”
Read more at: https://phys.org/news/2017-02-tenet-dominant-evolutionary-biology.html#jCp
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This makes sense. The longer a duplication exists, the more likely an organism may become dependent on it. But a newer duplications should be more conducive to beneficial mutations.
In these cases, the spontaneous mutation of one of the paralogous genes would be sufficient to create a situation where gene function is no longer assured. Duplication of the gene therefore made the genome more fragile.”