"The first meta-analysis (in 2004) put together data from more than 800 participants, and the second, in 2008, included more than 2,000 participants. In both meta-analyses they found “no significant sex difference in functional language lateralization.” Interestingly, they also found that studies that found sex differences tended to have smaller sample sizes than those that didn’t.

Several researchers have recently argued that gender differences in language skills are actually more or less nonexistent.17 The supposedly larger female corpus callosum, a claim built on shaky foundations, is under no less serious dispute.18 This research has been thoroughly examined and critiqued by Brown University professor of biology Anne Fausto-Sterling who, in Sexing the Body, explains the challenges of establishing the size of a particular structure in the brain. And a meta-analysis conducted by Katherine Bishop and Douglas Wahlsten in 1997 concluded that “the widespread belief that women have a larger splenium than men and consequently think differently is untenable.”19 Summarizing this literature in a 2008 review, cognitive neuroscientist Mikkel Wallentin concluded that “the alleged sex-related corpus callosum size difference is a myth.” The culprit? Look no further than “the possibility of ‘discovering’ spurious differences when using small sample sizes,” says Wallentin."

Fine, Cordelia. Delusions of Gender: How Our Minds, Society, and Neurosexism Create Difference (p. 138). W. W. Norton & Company. Kindle Edition.