Lonesome George died when he was about 101 years old. It was not particularly old for a Galapagos turtle, which can live 150 years, nor was it particularly large, weighing just 194 pounds compared to the normal weight of about 330 for the turtles' relatives. What makes Lonesome George worth studying was not his naturalness – it is the fact that he was the last of his kind.
Giant turtles are used to wander, albeit slowly, in much of the world. Big atlas he roamed in the Punjab region of India and Hesperotestudo crassiscutata crossed Central America in the southern United States. Their gigantism is not the result of life on islands – and then it was huge. It is precisely that the only surviving giant turtles lived in remote landings isolated from oceans in several tropical parts of the world where an evolving climate and a rapidly growing human population could make relatively minor damage to them.
We were too late to save the species of George, Chelonoidis abingdonii, but geneticists are still trying to combine the understanding of these giants by looking at Lonesome George's DNA. Even if it was not excellent, its genes are. As one of the long-standing organisms on Earth, C. abingdonii and other giant turtles are of interest to anyone who wants to understand how some animals are able to live for such extensive stretches.
This is why this international group of geneticists and biologists collected samples from Lonesome George and another giant turtle, analyzed their genes and compared them with a bunch of other creatures. They published their results in the magazine Nature Ecology & Evolution. This comparison allows geneticists to understand which genes appear at higher rates in long-lived turtles compared to other reptiles or mammals (we call this positive option). By discovering what pieces of DNA are comparatively more common among the huge turtles, researchers can begin to understand what kinds of traits help animals live longer. This does not mean that none of the specific genes they found are "the gene to live longer", but it means that gene sets may tend to allow a longer life.
The classic example has to do with telomere. At the end of all DNA strands are repetitive sequence sequences called telomeres that act as end caps for the individual strands. We all start with very long telomere because the cell-replicating machine is incomplete and can not replicate the entire strand – a small piece at the end is cut off at a time. If DNA fragments encoding important proteins were continuously cut off, our cells could not function for more than a few cycles of replication. Instead, we interrupted our telomere, which does not encode anything. The problem, of course, is that you can not develop them back, and finally your telomere is so close that the blister can not divide. This seems to contribute significantly to the process of developing old, so many anti-aging centers around the way either slow down the weakening of the telomeres or regenerate them after leaving.
The giant turtles, as determined by this study, have genetic variants in proteins that repair and preserve DNA, especially the telomeric segments. Researchers have taken it to indicate that the maintenance of telomeres can play an important role in keeping these turtles alive for so long.
But perhaps more interesting is how giant species like Lonesome George avoid one of the wounds of our modern existence: cancer. "An important feature of large, long-lived vertebrates is their need for stricter cancer protection mechanisms," the authors write in the paper, quoting something called Peto's paradox.
You have never heard of Peter or his paradox, so let us process.
Richard Peto is Professor of Medical Statistics and Epidemiology at Oxford University who observed that older animals do not receive cancer at higher rates than smaller animals. This may not seem important to you, but it is really amazing because larger animals have more cells. Cancer is simply a cell division disease – whenever a cell is divided, it must replicate its DNA, and this process is prone to mistakes. This means that each division is an opportunity for a mutation to occur. More branches lead to more mutations and more mutations increase the risk of turning a cell into cancer. Since larger animals have more cells, it makes sense to be more prone to cancer – they just experience more divisions. But they do not. Studies on body size and risk of cancer do not show a correlation between species. Within a species is a different story, though. Higher people seem to have higher rates of cancer, even after testing for potential confounders. This is not definitive proof, but it adds the data. If even a little older people seem to develop more cancers, then much older species must have evolved ways to avoid cancer – otherwise each turtle will die from it.
Turtles, despite their huge size, almost never seem to have cancer. Indeed, when these biologists glanced at the giant genus of the turtle, they found more copies of the genes known to suppress tumor formation, as well as duplicates for other genes that can help the immune system identify and kill potentially cancerous cells. All of these changes are minor in themselves, but together they suggest that giant turtles are generally better able to avoid cancer.
It is not going to fit into all the other individual findings in this document, because there are a ton of them, most of which are incredibly detailed and in-house. Turtles seem to have slower metabolism, for example, which some scientists believe can help slow down the aging process. They also have mutations that can help them better regulate glucose uptake and resist hypoxia. All of this will require further research to determine exactly which genes contribute to a longer life and how – this research is only the first step. There is much more work before these findings help us keep us young – or, more forcefully, to help us save other species of Galapagos turtle. For the time being, it's nice to know that Lonesome George could contribute something to our understanding of his type even after he left. He may have been the last one C. abingdonii, but it was first in our heart.