He divided the group into male and female camps and left them on an island.
After a few days the men had a water-tight shelter, a campfire with reserves of wood, they were hunting and fishing and generally dealing with the hardships. To be fair they didn't all get along but they worked together in common interest.
The women quickly split into cliques and invested their time and energy in rivalry. They built no shelter. They mostly slept and sunbathed. Half the group decided to go off on a recce. They spent 3 or 4 days totally lost and eventually made it back to camp with no intel, food or other resources - but lots of new causes for division.
Then the weather changed. The men were warm and dry and had food. The women were soaked, cold and hungry. They trekked to the men's camp and cried a lot.
The women had been supplied with a fishing net. They had caught nothing. The men offered to take the net, catch fish and share them with the women. The women told the men to f. off. The women went hungry.
To be fair there are women who could perform as well as many men in similar circumstances - there are one or two female candidates in the latest series of 'Who Dares Wins' who are very impressive. In general the results of the Bear Grylls experiment was entirely predictable. The best grouping would undoubtedly be a mix of male and female members but if it is single-sex, only one of those groups will survive.
Our brains evolved over hundreds of thousands of years on the Savannah where the ability to hunt, fight and navigate on the one hand, and nurture infants on the other, was a matter of life-and-death.