  This paper answers a basic question about the Birman exact sequence in the
theory of mapping class groups. We prove that the Birman exact sequence does
not admit a section over any subgroup $\Gamma$ contained in the Torelli group
with finite index. A fortiori this proves that there is no section of the
Birman exact sequence for any finite-index subgroup of the full mapping class
group. This theorem was announced in a 1990 preprint of G. Mess, but an error
was uncovered and described in a recent paper of the first author.
