In the latest episode of Genetics Unzipped, presenter Kat Arney takes a look at the genetics of giants and the science of small. Why do some species grow so large? What’s the genetic legacy behind the Giants of Ireland? And what was it about life on a Mediterranean island that miniaturised a mammoth?
Go big or go home
Giants have a knack of capturing the imagination. Whether it’s a new titanosaur, tales of mythical giants, towering redwoods, or the awe inspired by a close encounter with a whale, everyone loves REALLY BIG THINGS.
Dinosaurs are the most obvious of nature’s giants, such as the towering Titanosaur that may have measured up to 40 metres. But there are also plenty of others – some extinct and others still with us – including clams, beetles, rodents, squid, beavers, elk, birds, sloths and armadillos.
Go big or go home is a philosophy that goes way back in time. From the moment that multicellular organisms became a thing around 3-billion years ago, the stage was set for the emergence of absolutely massive organisms. There are giants – now extinct or occasionally still with us – in just about every multicellular branch of the tree of life.
However, with more size comes more problems. Big animals have large appetites so there’s a limit to how many giants any given ecosystem can sustain. This may help explain giants – every time they have evolved – do not last long. As geologist Geerat Vermeij puts it, “Large size has never been a long-term advantage.”
But if there’s one thing that the fossil record tells us, it’s that life always finds a way and that giants will emerge.
The Irish Giant
Kat also explores the story of Charles Byrne, the 18th century ‘Irish Giant’ who clocked in at an incredible 7 feet 7 inches. Despite Byrne’s wish to be buried at sea when he died, his skeleton somehow ended up in the collection of the anatomist John Hunter, eventually becoming part of the Hunterian museum.
Centuries later, researchers discovered the reason for his great height: a benign adenoma tumour in his pituitary gland, which meant that Byrne kept producing growth hormones long into adulthood. By isolating DNA from Byrne’s teeth, endocrinologist Marta Korbonits discovered a single DNA ‘letter’ change in the middle of a gene called AIP.
When she sequenced the DNA from patients with similar pituitary adenomas currently living in Ireland, she found they were all carrying the exact same alteration. In fact, the area where Byrne was born has an unusually high number of very tall people, and a higher prevalence of this genetic variant. It’s fair to say that Byrne – once touted as “the tallest man in the world” – has made a giant contribution to science.
Giants and dwarves
Finally, Kat goes island hopping to explore the science of insular dwarfism and gigantism – the phenomenon by which some animals evolve to become unusually small or large when trapped on islands.
We meet Welsh palaeontologist Dorothea Bate, who got a job at the Natural History Museum in 1898 and was probably the first woman ever employed as a scientist by the institution.
Her explorations of Mediterranean islands revealed a huge number of strangely sized animals including a species of unusually large mice on Crete, a huge, possibly flightless swan on Malta with a wingspan of around 3 metres, massive, fiercely-toothed shrews on Corsica and other islands, and a giant dormouse on Majorca that would have been about the size of a grey squirrel.
Best of all, she also discovered miniature elephants and mammoths, which only died out relatively recently in the past few thousand years.
At the same time as Bate was working in the Med, another researcher was finding examples of island dwarfism without even setting foot on a boat. Baron Ferenc (Franz) Nopcsa von Felső-Szilvás was a Hungarian aristocrat born in 1877, gained a PhD in geology by mapping the area surrounding his family estate. He discovered examples of miniaturised dinosaurs fossils which led him to suggest that the area was once an island.
He also found time to smuggle weapons and work undercover as a spy, hijack an aircraft, and jack in his job as head of the Hungarian Geological Institute to ride around Europe on a motorbike looking for fossils. A fascinating character!
Listen to the Genetics Unzipped podcast
Listen to the whole episode and find show notes and a full transcript at GeneticsUnzipped.com.
Genetics Unzipped is the podcast from the UK Genetics Society, presented by award-winning science communicator Dr Kat Arney and produced by First Create the Media. Follow Genetics Unzipped on Twitter @geneticsunzip, and the Genetics Society at @GenSocUK