  The evolution of thousands of orbits of Jupiter-family comets and asteroids
under the gravitational influence of planets was calculated. Comparison of the
results obtained by a symplectic method with those obtained by direct
integration showed that a symplectic method is not always good for
investigations of the orbital evolution of such bodies. Basing on the results
of orbital evolution of bodies, we concluded that a considerable portion of
near-Earth objects could have come from the trans-Neptunian region. Some large
trans-Neptunian objects could be formed by the compression of rarefied dust
condensations, but not by the accumulation of smaller planetesimals.
