Accumulating evidence indicates that some protein-coding genes have originated 
de novo from previously non-coding genomic sequences. However, the processes 
underlying de novo gene birth are still enigmatic. In particular, the appearance 
of a new functional protein seems highly improbable unless there is already a 
pool of neutrally evolving peptides that are translated at significant levels 
and that can at some point acquire new functions. Here, we use deep 
ribosome-profiling sequencing data, together with proteomics and single 
nucleotide polymorphism information, to search for these peptides. We find 
hundreds of open reading frames that are translated and that show no 
evolutionary conservation or selective constraints. These data suggest that the 
translation of these neutrally evolving peptides may be facilitated by the 
chance occurrence of open reading frames with a favourable codon composition. We 
conclude that the pervasive translation of the transcriptome provides plenty of 
material for the evolution of new functional proteins.