Traits are often lost during evolution, either because they are no longer beneficial or because they are too costly to maintain. When this happens, it is generally believed that the genes underlying the trait will eventually degrade as well, making it difficult if not impossible for the trait to re-emerge. Yet there are numerous examples in nature of once-lost traits re-emerging in descendent lineages.
ENDANGERED SPECIES ESSAY I'm still here. Don't let me go. ~Robert Krulwich Once deemed extinct in Lord Howe Island (LHI), where they are endemic, today