Two people are dancing a waltz, and it is not going well. One is tall and the other short; one is graceful, the other flat-footed; and both are stepping to completely different rhythms. The result is chaos, and the dance falls apart. Their situation mirrors a problem faced by all complex life on Earth. Whether we’re animal or plant, fungus or alga, we all need two very different partners to dance in step with one another. A mismatch can be disastrous.
Virtually all complex cells – better known as eukaryotes – have at least two separate genomes. The main one sits in the central nucleus. There’s also a smaller one in tiny bean-shaped structures called mitochondria, little batteries that provide the cell with energy. Both sets of genes must work together. Neither functions properly without the other.
Mitochondria came from a free-living bacterium that was engulfed by a larger cell a few billion years ago. The two eventually became one. Their fateful partnership revolutionised life on this planet, giving it a surge of power that allowed it to become complex and big (see here for the full story). But the alliance between mitochondria and their host cells is a delicate one.
Both genomes evolve in very different ways. Mitochondrial genes are only passed down from mother to child, whereas the nuclear genome is a fusion of both mum’s and dad’s genes. This means that mitochondria genes evolve much faster than nuclear ones – around 10 to 30 times faster in animals and up to a hundred thousand times faster in some fungi. These dance partners are naturally drawn to different rhythms.
This is a big and underappreciated problem because the nuclear and mitochondrial genomes cannot afford to clash. In a new paper, Nick Lane, a biochemist at University College London, argues that some of the most fundamental aspects of eukaryotic life are driven by the need to keep these two genomes dancing in time. The pressure to maintain this “mitonuclear match” influences why species stay separate, why we typically have two sexes, how many offspring we produce, and how we age.
In the caves of Slovenia and Croatia lives an animal that’s a cross between Peter Pan and Gollum. It’s the olm, a blind, cave-dwelling salamander, also called the proteus and the “human fish”, for its pale, pinkish skin. It has spent so long adapting to life in caves that it’s mostly blind, hunting instead with various supersenses including the ability to sense electricity. It never grows up, retaining the red, feathery gills of its larval form even when it becomes sexually mature at sweet sixteen. It stays this way for the rest of its remarkably long life, and it can live past 100.
The olm was once described as a baby dragon on account of its small, snake-like body. It’s fully aquatic, swimming with a serpentine wriggle, while foraging for insects, snails and crabs. It can’t see its prey for as it grows up, its eyes stop developing and are eventually covered by layers of skin. It’s essentially blind although its hidden eyes and even parts of its skin can still detect the presence of light. It also has an array of supersenses, including heightened smell and hearing and possibly even the ability to sense electric and magnetic fields.
Warning: Since writing this article, it has become clear that the research in question has some serious flaws that came to light after it was published and widely reported. The conclusions here should be treated with caution. UPDATE: The paper has since been retracted.
The developed world is an ageing one. In 2008, the number of pensioners in the UK exceeded the number of minors for the first time in history. Centenarians – those who’ve lived for a century or more – are our fastest-growing demographic. By 2030, ageing baby-boomers will swell the ranks of centenarians to around a million worldwide. That will have important implications, not just socially and economically, but scientifically too. The genomes of these ‘oldest old’ provide a window into the biology of ageing and the secrets to a longer (and healthier) life. It’s a window that Paola Sebastieni from Boston University School of Public Health has just peered through. By studying the genomes of over a thousand centenarians, she has developed a model that can predict a person’s odds of living into their late 90s and beyond with an accuracy of 77%. On the surface, this might seem like a very complicated piece of fortune-telling, but getting accurate predictions isn’t an end unto itself. The point of the exercise is to better understand the full complement of genetic variants that can affect our risk of living to an older age and doing so healthily.
An assortment of tree-living mammals
In The Descent of Man, Darwin talked about the benefits of life among the treetops, citing the “power of quickly climbing trees, so as to escape from enemies”. Around 140 years later, these benefits have been confirmed by Milena Shattuck and Scott Williams from the University of Illinois.
By looking at 776 species of mammals, they have found that on average, tree-dwellers live longer than their similarly sized land-lubbing counterparts. Animals that spend only part of their time in trees have lifespans that either lie somewhere between the two extremes or cluster at one end. The pattern holds even when you focus on one group of mammals – the squirrels. At a given body size, squirrels that scamper across branches, like the familiar greys, tend to live longer than those that burrow underground, like prairie dogs.
These results are a good fit for what we already know about the lives of fliers and gliders. If living in the trees delays the arrival of death, taking to the air should really allow lifespans to really take flight. And so it does. Flight gives bats and birds an effective way of escaping danger, and they have notably longer lives than other warm-blooded animals of the same size. Even gliding mammals too tend to live longer than their grounded peers.
People diet for many reasons – to fit into clothes, to look more attractive, or for the sake of their health. But to improve their memory? It’s an interesting idea, and one that’s been given fresh support by Veronica Witte and colleagues from the University of Munster in Germany.
Witte found that elderly people who slash the calories in their diet by 30% were better able to remember lists of words than people who stuck to their normal routine. It’s the first experiment to show that cutting calories can improve human memory at an age when declining memory is par for the course.
The benefits of low-calorie diets have been extensively studied in animals, ever since Clive McCay discovered that “caloric restriction” doubled the lifespan of rats, over 70 years ago. Many studies have found that such diets could help to slow the brain’s eventual decline and protect its neurons from the ravages of ageing. But until now, no experiments had confirmed that the same benefits are relevant to the human brain.