Okene's horrific ordeal is believed to be the longest amount of time that any human being has ever survived for underwater without the assistance of any diving equipment.
Living organisms for millions of years depended on their instincts to survive, over time for some animals this evolved from an instinct to a feeling of fear.
Various interventions, such as infection-fighting drugs, can increase a population's average survival time, but only approaches that slow the body's rate of aging will increase the maximum lifespan.
So individuals with mutations that reduced the length of their tails became more successful at life on land, surviving long enough to pass their short tails on to the next generation.