Using literature data on reciprocal crosses, I estimated the influence of maternal effects on morphological and behavioral traits and compared these effects between mammals, birds, insects with homogametic females, and butterflies. In birds and in both groups of insects, no detectable difference between the reciprocal hybrids was observed on average, showing that in these groups, the contribution of maternal effects to the difference between the parental lines is at least rather small. In contrast to the other groups, mammals showed a significant and large influence of maternal effects on the examined characters. The large maternal effects in mammals are probably due to the extended period of parental care during gestation and lactation. It is concluded that maternal effects contributing to differences between parental lines are only widespread and important in mammals. It should be noted that these results do not show that maternal effects are absent in other animals. In the three examined groups, maternal effects may only evolve much more slowly than traits influenced by nuclear genes.