Saturday, February 23, 2013

Why Larger Species Live Longer

Adrian Bejan, the J.A. Jones Professor of mechanical engineering at Duke and father of the Constructal Law, is the author of a paper (1) in which he tries to explain the longer lifespan of larger creatures. What Constructal Law says is that anything that flows, be it blood, a river, a jet stream, a highway system, will evolve toward a similar mathematical configuration to maximize efficiency.

It's all about Math.
He then proposes to look at an animal simply as a flowing mass in motion. Mathematically calculating the size and age of both animate and inanimate objects, he found the same correlation: larger rivers are older, larger jet streams last longer, larger animals live longer. They all also cover larger territories of travel.

Breaths of Life.
Even more interesting, however, is the finding that if body size and lifespan of animals are plotted on a curve, they fall on a slope of about ¼. And then, if you plot the frequency of breathing to body size, it forms a slope of - ¼. Combining the two lines of inquiry he found that an animal has a constant number of breaths per lifetime. (2) The larger animals breathe more slowly in order to cover a longer lifespan.

Monday, February 11, 2013

Do We Really Want Physical Immortality? Part II

Psychological Consequences

· Belief in religion – One of the main functions of most religions is to provide an answer to the question of what happens after death. The immortality of the soul is an essential part of most religious traditions. If we have immortality of the physical body, would there still be the same need for religion?

· The big questions. Existing indefinitely in the physical world would prevent us from getting the answers to the big questions: is there a soul, is there life after death, is there a reason for our existence, does God exist? We will be forever relegated to living in the black box of the physical world. Or maybe there is a way of getting out of it without dying?

· Risk aversion. If life is indefinitely long, there would be a lot more to lose. People may restrict their daily actions to reduce the chance of being severely injured or losing one’s life. Sports like skiing, hokey, football, skydiving, mountain climbing, car racing and so on may no longer be tolerated. Even driving a car or traveling by any mode of transportation may be seen as too dangerous. A time may come when people will no longer even be willing to leave their homes. They will just live in cyberspace, letting their avatars take all the chances.

Saturday, February 9, 2013

Do We Really Want Physical Immortality? Part I

There are many theories that try to describe the biological cause of aging. They include the antagonistic pleiotropy hypothesis, the astrocytic hypothesis, DNA damage theory, evolutionary theory, free-radical theory, network theory, reliability theory, reproductive cell cycle theory, stem cell theory and others. But to quote David Rollo, “In any field of science, the true degree of understanding is inversely proportional to the number of explanatory theories that prevail.”

Programmed to die.
Whatever the details, the fundamental basis for aging has to reside in our DNA. Each species has its own particular average lifespan (excluding a few that seem to be “immortal” by regressing to an earlier stage). DNA is a code—a very complicated code, but a code nonetheless. With our computational abilities increasing at an exponential rate, it is clear that one day—maybe in 50, maybe in 100 years—we will break that code and find a “cure” for aging.

Saturday, February 2, 2013

The Longevity Gene

A new study published on January 31, 2013 in the journal Cell Reports (1) found that by infusing the blood stem cells of old mice with a so-called “longevity gene,” SIRT3, they were able to rejuvenate their regenerative potential, in effect to become younger.

SIRT3 is a protein among a class known as sirtuins which are known to regulate the aging process. SIRT3 is found in a cell’s mitochondria, which has its own DNA apart from that of the nucleus. Previous studies have shown that the SIRT3 gene is activated during caloric restriction, and that caloric restriction extends lifespan in some species, though that hasn’t yet been shown in humans.

Studies have shown that having an extra copy of another sirtuin, SIRT2, extends the lifespan of yeast, worms and flies. (2) In mammals there are now known to be at least seven sirtuins (SIRT1-SIRT7).