The Swedish Psychologist K. Anders Ericsson has published many reports stating that talent is "made and not born". In his book 'The Cambridge Handbook of Expertise and Expert Performance', he has stated that "Consistently and overwhelmingly, the evidence showed that experts are always made, not born."
On the other hand, a recent twin study has stated that on average, a human's ability is 50% influenced by genetic factors, and 50% influenced by environmental factors. This seems to contradict Ericsson's experiment, as he has asserted that genetic factors influence a person's abilities by less than 1%.
Does the twin study contradict Ericsson's assertions, and if so, why would there be such a large contradiction? What factors could have caused these large differences in findings?