“How?” asked Desh, not wanting to have the conversation bog down but unable to repress his curiosity. “Just give me the Cliffs Notes version.”
Kira paused, as if considering how best to frame her response. “As I said before, our brains aren’t optimized for thought. Well, not surprisingly, our bodies aren’t optimized for longevity either. Again, all natural selection cares about is reproduction.” She took a sip of iced-tea and set it back down on the table. “If you have a mutation that enhances your ability to survive to childbearing age, this mutation will preferentially appear in future generations. But longevity genes don’t kick in until you’ve already done all the reproducing you’re ever going to do. The guy who dies at forty has just as much chance of having scores of children, and passing on his poor longevity genes, as the guy who dies at eighty has of passing on his good ones. There’s no evolutionary advantage to long life.”
Desh’s eyes narrowed. “But parents who live longer can increase their offspring’s chances of survival. So longevity genes should confer an advantage.”
“Very good,” she said. “This is true. There is evolutionary pressure on our genes to keep us alive long enough to ensure our children can take care of themselves. But after this point there’s no advantage to further longevity. In fact, there might even be evolutionary pressure against it.”
Desh looked confused.
“The elderly can be a burden on the clan when resources are scarce,” explained Kira. “Decreasing the chances of survival for future generations.”
A look of distaste came over Desh’s face. “So those clans whose elders have the decency to drop-dead early on and not drain further resources thrive more than those whose elders live forever?”
“During times of scarcity at least, yes. This is one probable explanation for why most life on Earth, including ours, is programmed to die.”
Desh’s brow furrowed in confusion. “What does that mean?” he said “I thought aging was the result of errors accumulating in our DNA.”
“Partially true. But a large part of aging is due to a form of planned obsolescence. Our immune systems weaken, we stop producing hormones like estrogen, our hair grays or falls out, our skin shrivels, the acuity of our hearing diminishes, and so on. Our bodies are programmed, at the level of our genes, to die.”
“You’re the scientist, but it’s hard for me to believe that’s true.”
“That’s because it happens gradually,” she said. “In some species, like pacific salmon and marsupial mice, it happens all at once. One day they have no signs whatsoever of aging and the next—bam—they’re dead from old age.” She paused. “Other species aren’t programmed to die at all, like rockfish and certain social insect queens.”
Desh tilted his head. “But they do die, right?”
“They die. They just don’t age as we know it. Eventually accidents or predators or starvation kills them.”
Desh had further questions but knew that now was not the time. “Go on,” he said.
“I studied these species extensively to understand why they didn’t age. I also took DNA samples from people who suffer from a rare aging disease called progeria. By the age of twelve progerics look and sound like elderly people.”
Desh shook his head sympathetically. “I’ve heard about that. What a horrible disease.”
He paused. “Can I at least assume their DNA was illuminating?”
“Very. It led directly to the breakthrough I needed,” she said. “I had been studying everything I could find on the molecular basis of aging for years. But when I added data on the genetic differences between progeria victims and normals my optimized brain was able to put all the pieces together.”
“And you’re positive your treatment will work? That it really will double the span of human life?”
“Absolutely certain,” she said without hesitation. “One hundred percent.”
Desh had become stiff from his angled position in the booth as he continued to watch the entrance, and he shifted temporarily into a more comfortable position. “How can you be so sure?” he asked, rubbing the back of his neck with his left hand while continuing to grip the gun with his right.
“There are a number of ways,” replied Kira. “But you’d need a much deeper knowledge of molecular biology and medicine to understand most of them. One way is to look at cellular doubling times. Most people don’t know this, but most of your cells will only divide about fifty times in culture. This is called the Hayflick limit. As they approach fifty doublings they take longer and longer to divide and show signs of aging.”
“What happens after they divide fifty times?” asked Desh.
“They die,” she said simply.
Desh pondered this for a few seconds. “What about cancer cells?” he asked.