The orbital distributions of prominent asteroid families are thought to be
direct by-products of catastrophic disruption events among diameter D great
er than or similar to 100 kilometer bodies. Ejection velocities derived fro
m studying observed families, however, are surprisingly high compared with
results from impact experiments and simulations. One way to resolve this ap
parent contradiction is by assuming that D less than or similar to 20 kilom
eter family members, since their formation, have undergone semimajor axis d
rift by the thermal force called the Yarkovsky effect. interactions between
drifting family members and resonances can also produce unique eccentricit
y and/or inclination changes. Together, these outcomes help explain (i) why
families are sharply bounded by nearby Kirkwood gaps, (ii) why some famili
es have asymmetric shapes, and (iii) the curious presence of family members
on short-lived orbits.