Attempts to determine the sex of prehistoric hand-stencil artists have turned up contradicting conclusions. Researchers in England and South Africa suggest focusing on hand size and finger length is unreliable.

To solve the problem, scientists adopted a forensics technique to yield more definitive results. Scientists believe the new analysis strategy can sex 40,000-year-old hand stencils with 90 percent accuracy.

"The problem with focussing on hand size and finger length is that two different shaped hands can have identical linear dimensions and ratios," Patrick Randolph-Quinney, a forensic anthropologist at the universities of Central Lancashire and Witwatersrand, said in a news release. "To capture shape, we applied geometric morphometrics, a technique used in forensic studies that had never been tested on hand stencils before."

Researchers developed the technique by training a computer model to translate 2D stencils into 3D hands. Scientists armed their model with data from known-sex hand stencils and the hands that created them. The model identified series of 2D landmarks linked with hand shape and form, and highlighted the correlations most predictive of sex.

"This geometric approach is very powerful as it allows us to look at the palm and fingers independently," Randolph-Quinney said. "It revealed that the shape of the palm is actually most indicative of the sex of the individual, rather than the finger size or length."

The oldest hand stencils -- at least 40,000 years old -- are found in Indonesia. Hand stencils found in the caves of Europe are thought to be 37,000 years old.

The new technique hasn't yet been used to analyze actual prehistoric hand stencils. Scientists want their technique to be tested on a variety of ethnicities and populations to confirm its validity.

"We would encourage other researchers to apply this method to different human populations so we can build a more global understanding of hand variation," said Anthony Sinclair, an archaeologist at the University of Liverpool.

The new research was published in the Journal of Archaeological Science.