"This kind" being the research we've been discussing, which is about socialisation and toy preference. Finger length and other easily-measured physical differences haven't been part of it.
It's briefly mentioned in the article as a possible indicator of toy preference because it correlates well with hormone levels. It clearly wasn't what the research, the discussion, or any of my comments were focusing on.
It's reported in all of the child studies discussed in TFA. Fault the article if you want but "hormones" is in the title, and the whole point of the entire line of research is that it's implausible that prenatal hormone levels could be affected by cultural biases.
The hormone levels are unlikely to be affected by cultural biases but that's not the potential weakness I'm talking about in these studies. It's during the observation, through the eyes of the parents and scientists, of what toys the children are playing with where expectations can affect the results. On top of that, you've got biases affecting what studies get published and which of those then make headlines and get repeated in blog posts like this one.
