Jonathan the Tortoise, World's Oldest Land Animal, Turns 190

Jonathan the tortoise, older than the Eiffel Tower and has survived two World Wars, seven British monarchs, and 39 U.S. presidents, is now celebrating his 190th birthday.

How come turtles have such long lives? According to Lori Neuman-Lee, an assistant professor of physiology at Arkansas State University who studies turtles and other reptiles, there are biological and evolutionary explanations for the phenomenon.

The evolutionary explanation is relatively simple: Animals like snakes and raccoons like eating turtle eggs. Turtles must regularly reproduce, sometimes more than once yearly, and deposit many eggs to pass on their genes. Given how many children turtles produce, Neuman-Lee said to Live Science, "It is astonishing that turtles do not overrun the globe."

More complex biological processes underlie the lifespan of turtles.

According to Neuman-Lee, telomeres, which are structures made up of noncoding DNA strands and cap the ends of chromosomes, is one indicator of turtle lifespan. As cells divide, these structures aid in chromosomal protection. Telomeres shorten or deteriorate over time, which makes them less effective in protecting chromosomes and causes problems with DNA replication. Also, DNA replication mistakes can result in problems, including tumors and cell death.

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