A large-scale population study of early life factors influencing left-handedness

Abstract

Hand preference is a conspicuous variation in human behaviour, with a worldwide proportion of around 90% of people preferring to use the right hand for many tasks, and 10% the left hand. We used the large cohort of the UK biobank (~500,000 participants) to study possible relations between early life factors and adult hand preference. The probability of being left-handed was affected by the year and location of birth, likely due to cultural effects. In addition, hand preference was affected by birthweight, being part of a multiple birth, season of birth, breastfeeding, and sex, with each effect remaining significant after accounting for all others. Analysis of genome-wide genotype data showed that left-handedness was very weakly heritable, but shared no genetic basis with birthweight. Although on average left-handers and right-handers differed for a number of early life factors, all together these factors had only a minimal predictive value for individual hand preference.

A sinister subject: Quantifying handedness‐based recruitment biases in current neuroimaging research

“…It is worth noting that when our data were limited to articles reporting at least one adextral participant, average adextral representation rose to around 12%. This value is more consistent with whole‐population prevalence rates of adextrality (given that estimates range between 10% and 13%; de Kovel et al., ; Gilbert & Wysocki, ; Peters et al., ), and highlights and interesting feature of the data: while most studies focused exclusively on dextral participants, those that did not recruite adextral and dextral participants proportional to the representation of each at the whole‐population level. This finding should dispel potential concerns that the observed bias in the overall sample is simply due to lack of available and eligible adextral participants.…”

“…Based on past work such as Willems et al. () and anecdotally observed trends, we predicted that this effort would reveal a disproportionate bias in favour of dextral recruitment, evidenced by less than 10% of research subjects—the lower end of estimated prevalence rates for adextrality (Gilbert & Wysocki, ; de Kovel et al., ; Peters et al., )—being classified as adextral.…”

“…Handedness refers to an individual's preferential use of one hand for fine manual tasks, such as writing, eating and using tools. While the majority of human beings are right‐handed (dextral), approximately 10%–13% of the human population are adextral, showing either no preference (ambidextrous) or a left‐handed preference for most manual tasks (Gilbert & Wysocki, ; de Kovel, Carrión‐Castillo, & Francks, ; Peters, Reimers, & Manning, ). Despite their sizable representation at the population level, adextrals are often overlooked by research in human neuroscience.…”

The genetics of situs inversus without primary ciliary dyskinesia

“…In utero environmental effects such as prenatal drug exposure might also affect left-right determination 87 . As regards handedness, this is known to associate with various early life factors including birthweight and breastfeeding, although not to a degree which is remotely predictive at the individual level 88 . As noted in the introduction, left-handedness has a heritability of roughly 25% in family and twin studies, and lower in SNP-based heritability studies.…”

Different laterality indexes are poorly correlated with one another but consistently show the tendency of males and females to be more left- and right-lateralized, respectively

“…In fact, it is well established that environmental pressures might force the use of the right hand for writing in left handers [13]. This phenomenon was mainly observed in past generations, and still applies to some cultures [1,14]. The EHI, similarly to other handedness questionnaires, leads to scores with a J-shaped distribution, indicating that the majority of people present an overall right-or left-hand preference with a few individuals in between.…”