Unit 42 Answer to the Mystery of Life Is Four Scientists have found a simple mathematical relationship that connects the whole nature, from the tiniest cell to the vast forest of the Amazon. The connections are all based on the three dimensions of the physical world -- length, depth and width -- plus one, making the number 4. "Four is the magic number of life," says Dr. Geoffrey West of the Santa Fe Institute in New Mexico, a keynote speaker at the NZ Institute of Physics annual conference last week. Dr. West, a British-born physicist, and US ecologists James Brown and Brian Enquist have found more than 50 biological relationships, such as between body size and heart rate, which are based on numbers taken to the power of 1/4. Much of the theory is based on mathematics that can confuse the mind of anyone who struggled through School Certificate maths. Suffice to say that it centers on equations involving square roots and numbers to the power of 1/4. In simple maths, says Dr. West, "if you are 16 times bigger than your dog, your heart rate is half the dog's rate." Average body size and lifetime are also related in the same ratio. So in principle, if you are 16 times the size of your dog, you will live twice as long. We do better than that, thanks to modern medicine, but the average lifetime of pre-European Maori was around 30. Remarkably, combining these two relationships means that the heart of every mammal beats roughly the same number of times in its average lifetime -- around 1.5 billion times -- regardless of whether it is a dog or a human, a mouse or an elephant. The implication is clear -- we can't beat nature. "This says that there is a maximum lifespan for a given size," Dr. West says. He and his colleagues have found that similar "quarter-power" rules govern every kind of life on Earth, from the rate at which single-celled bacteria absorb energy to the height of those Amazon trees. They believe this uniformity is because every living thing is made up of distribution networks carrying blood, air and other nutrients first through big tubes such as the aortic artery and then through a succession of smaller tubes to the capillaries, which finally distribute the nutrients to cells. Within each class of the last stage of the chain, species, such as mammals, the size of the capillaries, is the same. So are the cells that we are all made of. But as the organism gets bigger, the distribution network increases more than would be expected -- as if it had a fourth dimension. It is this increase in dimensionality that accounts for the 4. The 4 represents actually 3 + 1, where 3 is the dimensionality of the space we live in. Auckland University physicist Dr. Peter Wills says the theory developed by Dr. West and his colleagues is widely accepted, even though it is still being developed. "There is a great deal of interest in the approach he has taken," Do. Wills said. "I don't know anybody who thinks it's nonsense.