New proteins and modules have been invented throughout evolution. Gene "bir
th dates" in Caenorhabditis elegans range from the origins of cellular life
through adaptation to a soil habitat. Possibly half are "metazoan" genes,
having arisen sometime between the yeast-metazoan and nematode-chordate sep
arations. These include basement membrane and cel adhesion molecules implic
ated in tissue organization. by contrast epithelial surfaces facing the env
ironment have specialized components invented within the nematode lineage.
Moreover, interstitial matrices were likely elaborated within the vertebrat
e lineage. A strategy for concerted evolution of new gene families, as well
as conservation of adaptive genes, may underlie the differences between he
terochromatin and euchromatin.