A human cell can divide roughly 50 times before it dies out. It's called the Hayflick limit, and it's become a real headache for the anti-aging science. As long as the limit holds, it suggests a maximum human lifespan of 120 years — but a new crop of research suggests the limit may not be as hard as we thought. Under lab conditions, mouse cells can keep dividing forever, while other animal cells only require smaller quantities of oxygen to keep dividing beyond their Hayflick limit. Another hopeful trend involves telomeres, the shortening DNA sequence once thought to represent humanity's biological clock. Recent studies indicated that telomere's aren't as important in aging as we thought, and can be rebuilt with the right enzymes. That's not a silver bullet, but it's reason to believe the 120-year limit isn't as hard and fast as scientists previously thought.