Reared-apart/reared-together Chinese twins and virtual twins: Evolving research program and general intelligence findings.

China's One-Child Policy (1979-2015) limited rural families to two children and urban families to one child. This practice, which led to the abandonment of hundreds of thousands of female infants, is indirectly responsible for the separate placement of infant twins. The availability of this sample launched the first prospective study of these pairs. Participants include families and twins comprising 15 monozygotic (MZA) pairs and 7 dizygotic (DZA) pairs from countries throughout the world. The research program is described, and the initial wave of IQ scores for MZA and DZA twin pairs is examined in the first comprehensive report from this study. The twins' mean age at participation was 9.41 years (SD = 6.36), and their ages ranged from 3.19 to 24.98 years. Informative contrasts with adopted-together Chinese twins and virtual twins (same-age unrelated individuals reared together) highlight shared genetic and environmental effects on intellectual development. Applied directions based on findings from these novel samples are described.

Fullerton Virtual Twin Project: Overview and 2019 Update.

Virtual twins (VTs) are defined as same-age unrelated siblings raised together from early infancy. This special class of adoptive siblings replays the rearing situation of twins, absent genetic relatedness. The first such pair was identified and studied in 1990 at the University of Minnesota, leading to the creation of the Fullerton Virtual Twin Study (FVTS) at California State University, Fullerton (CSUF) the following year. The registry currently includes 169 VT pairs, mostly children, with new pairs identified on a regular basis. These sibling sets provide a direct estimate of environmental influences on developmental traits and, as such, offer informative comparisons with ordinary monozygotic and dizygotic twins, full siblings and adoptive brothers and sisters. The sample characteristics, assessment battery and findings to date are summarized in this 2019 update.

Senatorial signatures Absence of male-female differences in left-handedness.

A greater frequency of left-handedness among males than females has been observed in general populations. Past studies have explained this difference with reference to males' greater susceptibility to adverse birth events, while more recent studies have identified other contributing factors. On January 16, 2020, U.S. senators signed an oath to act impartially during the president's impeachment trial. This televised event allowed direct comparison of the proportion of right-handedness and left-handedness in a professionally accomplished sample of males and females. As expected, no sex difference in the proportion of left-handed senators was found, although the small sample size offered low statistical power. Replicating this finding with a larger sample would support the view that left-handedness among select groups of males is linked to genetic factors.