Do parents favor their adoptive or biological children? Predictions from kin selection and compensatory models

Evolutionary reasoning (Kin Selection Theory) predicts less favorable behaviors directed by parents toward their unrelated children, relative to their biologically related children. By extension, it may be argued that parents should also have less favorable perceptions of the intellectual, personality and other behavioral traits of unrelated children, compared with biologically related children. However, recent work has modified this expectation, given the distinction between unrelated adopted children (who are acquired intentionally) and unrelated stepchildren (who are acquired via mating effort). The compensatory model takes into account evolved desires for parenting and the evolutionarily novel availability of unrelated children. It predicts that adopted children may be viewed as favorably, or even more favorably, than biological children due to parents' compensation for the perceived challenges and stigma linked to their exceptional family structure. In the present study, IQ Adjective Checklist and Child Behavior Checklist scale scores were available for 135 virtual twin pairs (same-age unrelated siblings raised together). Virtual twins included 41 adopted-biological pairs and 94 adopted-adopted pairs, with a mean age of 6.14 years (SD = 3.51). These unique data allowed tests of hypotheses and predictions concerning parenting perceptions, given the matched age and placement of the biological and adoptive siblings. Consistent with prior research, the IQ scores of the biological children exceeded those of the adopted children, both between and within pairs. A between-pair analysis revealed no difference between biological children and members of adopted-adopted pairs in ratings of favorable or unfavorable traits. However, more telling within-family comparisons of adopted-biological pairs revealed higher scores for adoptees on unfavorable traits, consistent with Kin Selection Theory, but no differences between adoptive and biological children on favorable traits, consistent with the compensatory model. These ...