This was true in the 19th century and it's still true in the 21st century. A gap in human knowledge is a research opportunity, not a hiding place for the god of the gaps. Scientific research will eventually solve every problem.

The Descent of Man (1871)

Ignorance more frequently begets confidence than does knowledge: it is those who know little, and not those who know much, who so positively assert that this or that problem will never be solved by science.

• It has often and confidently been asserted, that man's origin can never be known: but ignorance more frequently begets confidence than does knowledge: it is those who know little, and not those who know much, who so positively assert that this or that problem will never be solved by science.