The phenomenon of de novo gene birth from junk DNA is surprising, because random 
polypeptides are expected to be toxic. There are two conflicting views about how 
de novo gene birth is nevertheless possible: the continuum hypothesis invokes a 
gradual gene birth process, while the preadaptation hypothesis predicts that 
young genes will show extreme levels of gene-like traits. We show that intrinsic 
structural disorder conforms to the predictions of the preadaptation hypothesis 
and falsifies the continuum hypothesis, with all genes having higher levels than 
translated junk DNA, but young genes having the highest level of all. Results 
are robust to homology detection bias, to the non-independence of multiple 
members of the same gene family, and to the false positive annotation of 
protein-coding genes.