Here’s the eighth piece from my BBC column
Tens of thousands of years ago, woolly mammoths roamed the northern hemisphere. These giant beasts may now be extinct, but some of their bodies still remain in the frozen Arctic wilderness. Several dozen such carcasses have now been found, and some are in extremely good condition. Scientists have used these remains to discover much about how the mammoth lived and died, and even to sequence most of its genome. But can they also bring the animal back from the dead? Will the woolly mammoth walk again?
Akira Iritani certainly seems to think so. The 84-year-old reproductive biologist has been trying to clone a mammoth for at least a decade, with a team of Japanese and Russian scientists. They have tried to use tissues from several frozen Siberian specimens including, most recently, a well-preserved thighbone. Last year, Iritani told reporters, “I think we have a reasonable chance of success and a healthy mammoth could be born in four or five years.”
A few months ago, a second team led by Korean scientist Hwang Woo Suk also expressed interest in cloning a mammoth. While Iritani comes with impressive credentials, Hwang’s resume is less reassuring. He is perhaps best known for faking experiments in which he claimed to have cloned the first human embryo and produced stem cells from it. The fact that he has confessed to buying mammoth samples from the Russian mafia does not help to instil confidence.
Regardless of their pedigree, both teams have their work cut out. Any attempt to resurrect the mammoth faces an elephantine gauntlet of challenges, including the DNA-shattering effects of frost and time, and the rather unhelpful reproductive tract of the eventual surrogate parent—the elephant.
In the desert of the United Arab Emirates, there is an unusual series of flat discs imprinted in the sand. Each one is about 40 centimetres wide, and they snake off into the distance in several parallel lines, for hundreds of metres.
They are tracks. They were made by a herd of at least 14 early elephants, marching across the land between 6 and 8 million years ago. The track-makers are long dead, but in the intervening time, nothing has buried their tracks or eroded them away. Today, their social lives are still recorded in their fossilised footsteps.
It turns out that elephants have a sixth toe. They’ve adapted one of their wrist bones into a strut that supports their giant squishy feet. I wrote about this for Nature (excerpt below), but here’s my full interview with John Hutchinson, the man behind the discovery, and the owner of (probably) the world’s largest collection of frozen elephant feet.
Elephants walk on the world’s biggest platform shoes. Now, John Hutchinson at the Royal Veterinary College in London and his team have found that their footwear also contains hidden stiletto heels.
Even though an elephant’s leg looks like a solid column, it actually stands on tip-toe like a horse or a dog. Its heel rests on a large pad of fat that gives it a flat-footed appearance. The pad hides a sixth toe — a backward-pointing strut that evolved from one of their sesamoids, a set of small tendon-anchoring bones in the animal’s ankle.
This extra digit, between 5 and 10 centimetres long, had been dismissed as an irrelevant piece of cartilage. Almost 300 years after it was first described, Hutchinson finally confirmed that it is a true bone that supports the squishy back of the elephant’s foot. The ones on the hindfeet even seem to have joints.
To round off my brief stint at the Guardian, here’s a piece about a mastodon specimen with what looks like a spear-tip stuck in its rib. This specimen, the so-called “Manis mastodon” has been a source of controversy for several decades. Is that fragment man-made or simply one of the animal’s own bone splinters? Does it imply that humans hunted large mammals hundreds of years earlier than expected, or not?
Having re-analysed the rib in an “industrial-grade” CT scanner, Michael Waters thinks it’s definitely a man-made projectile. He even extracted DNA from the rib and the fragment and found that both belonged to mastodons. So these early hunters were killing mastodons and turning them into weapons for killing more mastodons. How poetically gittish.
Anyway, read the piece for more about why this matters. In the meantime, I want to draw your attention to this delicious tete-a-tete at the end between Waters and Gary Haynes, who doesn’t buy the interpretation. Note, in particular, the very last bit from Waters, which made my jaw drop.
But despite Waters’ efforts, the fragment in the Manis mastodon’s rib is still stoking debate. “It’s not definitely proven that it is a projectile point,” says Prof Gary Haynes from the University of Nevada, Reno. “Elephants today push each other all the time and break each other’s rib so it could be a bone splinter that the animal just rolled on.”
Waters does not credit this alternative hypothesis. “Ludicrous what-if stories are being made up to explain something people don’t want to believe,” he says. “We took the specimen to a bone pathologist, showed him the CT scans, and asked if there was any way it could be an internal injury. He said absolutely not.”
Waters adds, “If you break a bone, a splinter isn’t going to magically rotate its way through a muscle and inject itself into your rib bone. Something needed to come at this thing with a lot of force to get it into the rib.”
The spear-thrower must have had a powerful arm, for tThe fragment would have punctured through hair, skin and up to 30 centimetres of mastodon muscle. “A bone projectile point is a really lethal weapon,” says Waters. “It’s sharpened to a needle point and little greater than the diameter of a pencil. It’s like a bullet. It’s designed to get deep into the elephant and hit a vital organ.” He adds, “I’ve seen these thrown through old cars.”
In natural history films, lionesses are usually portrayed as the hunters of the pride, while male lions mope around under shady trees. But males are no layabouts – they’re effective killers in their own right, particularly when they target larger prey like elephants and buffalo. Aside from humans, lions are the only predators powerful enough to kill an elephant. The males, being 50% heavier than the females, are especially suited to the task. It typically takes seven lionesses to kill an elephant, but just two males could do the same.
Even a single male can overpower a young elephant. Between 1994 and 1997, Dereck Joubert found that the lions of Botswana’s Chobe National Park were getting better and better at hunting elephants. He wrote: “In one notable case, a single male lion ran at nearly full speed into the side of a 6-year-old male calf with sufficient force to collapse the elephant on its side.”
Male lions clearly pose a great threat, and older elephants know it. Karen McComb from the University of Sussex has found that older matriarchs – the females who lead elephant herds – are more aware of the threat posed by male lions. If they hear recordings of male roars, they’re more likely to usher their herd into a defensive formation. Their experience and leadership could save their followers’ lives. “Family units led by older matriarchs are going to be in a position to make better decisions about predatory threats, which is likely to enhance the fitness of individuals within the group,” says McComb.
In Lampang, Thailand, two elephants have a problem. They’ve walked into adjacent paddocks separated by a fence. In front of them is a sliding table with two food bowls, but it’s out of reach and the way is barred by a stiff net. A rope has been looped around the table and one end snakes into each of the paddocks. If either jumbo tugs on the rope individually, the entire length will simply whip round into its paddock, depriving both of them of food. This job requires teamwork.
And the elephants know it. Joshua Plotnik from Emory University has shown that when confronted by this challenge, elephants learn to coordinate with their partners. They eventually pull on the rope ends together to drag the table towards them. They even knew to wait for their partner if they were a little late. It’s yet more evidence that these giant animals have keen intellects that rival those of chimps and other mental heavyweights.
It’s a classic David and Goliath story, except there are 90,000 Davids and they all have stings. On the African plains, the whistling-thorn acacia tree protects itself against the mightiest of savannah animals – elephants – by recruiting some of the tiniest – ants.
Elephants are strong enough to bulldoze entire trees and you might think that there can be no defence against such brute strength. But an elephant’s large size and tough hide afford little protection from a mass attack by tiny ants. These defenders can bite and sting the thinnest layers of skin, the eyes, and even the inside of the sensitive trunk. Jacob Goheen and Todd Palmer from Kenya’s Mpala Research Centre have found that ants are such a potent deterrent that their presence on a tree is enough to put off an elephant.
At first glance, the African elephant doesn’t look like it has much in common with us humans. We support around 70-80 kg of weight on two legs, while it carries around four to six tonnes on four. We grasp objects with opposable thumbs, while it uses its trunk. We need axes and chainsaws to knock down a tree, but it can just use its head. Yet among these differences, there is common ground. We’re both long-lived animals with rich social lives. And we have very, very large brains (well, mostly).
But all that intelligence doesn’t come cheaply. Large brains are gas-guzzling organs and they need a lot of energy. Faced with similarly pressing fuel demands, humans and elephants have developed similar adaptations in a set of genes used in our mitochondria – small power plants that supply energy to our cells. The genes in question are “aerobic energy metabolism (AEM)” genes – they govern how the mitochondria metabolise nutrients in food, in the presence of oxygen.
We already knew that the evolution of AEM genes has accelerated greatly since our ancestors split away from those of other monkeys and apes. While other mutations were reshaping our brain and nervous system, these altered AEM genes helped to provide our growing cortex with much-needed energy.
Now, Morris Goodman from Wayne State University has found evidence that the same thing happened in the evolution of modern elephants. It’s a good thing too – our brain accounts for a fifth of our total demand for oxygen but the elephant’s brain is even more demanding. It’s the largest of any land mammal, it’s four times the size of our own and it requires four times as much oxygen.
Goodman was only recently furnished with the tools that made his discovery possible – the full genome sequences of a number of oddball mammals, including the lesser hedgehog tenrec (Echinops telfairi). As its name suggests, the tenrec looks like a hedgehog, but it’s actually more closely related to elephants. Both species belong to a major group of mammals called the afrotherians, which also include aardvarks and manatees.
Goodman compared the genomes of 15 species including humans, elephants, tenrecs and eight other mammals and looked for genetic signatures of adaptive evolution. The genetic code is such as that a gene can accumulate many changes that don’t actually affect the structure of the protein it encodes. These are called “synonymous mutations” and they are effectively silent. Some genetic changes do, however, alter protein structure and these “non-synonymous mutations” are more significant and more dramatic, for even small tweaks to a protein’s shape can greatly alter its effectiveness. A high ratio of non-synonymous mutations compared to synonymous ones is a telltale sign that a gene has been the target of natural selection.
And sure enough, elephants have more than twice as many genes with high ratios of non-synonymous mutations to synonymous ones than tenrecs do, particularly among the AEM genes used in the mitochondria. In the same way, humans have more of such genes compared to mice (which are as closely related to us, as tenrecs are to elephants).
These changes have taken place against a background of less mutation, not more. Our lineage, and that of elephants, has seen slower rates of evolution among protein-coding genes, probably due to the fact that the duration of our lives and generations have increased. Goodman speculates that with lower mutation rates, we’d be less prone to developing costly faults in our DNA every time it was copied anew.
Overall, his conclusion was clear – in the animals with larger brains, a suite of AEM genes had gone through an accelerated burst of evolution compared to our mini-brained cousins. Six of our AEM genes that appear to have been strongly shaped by natural selection even have elephant counterparts that have gone through the same process.
Of course, humans and elephants are much larger than mice and tenrecs. But our genetic legacy isn’t just a reflection of our bigger size, for Goodman confirmed that AEM genes hadn’t gone through a similar evolutionary spurt in animals like cows and dogs.
Goodman’s next challenge is to see what difference the substituted amino acids would have made to us and elephants and whether they make our brains more efficient at producing aerobic energy. He also wants to better understand the specific genes that have been shaped the convergent evolution of human and elephant brains over the course of evolution. That task should certainly become easier as more and more mammal genomes are published.
Reference: PNAS doi:10.1073/pnas.0911239106
More on elephants:
This is a bull elephant firmly establishing why it is he, and not the lion, who is king of beasts. The elephant’s penis is not only massive but prehensile. As we watched in baffled amusement (and the faintest tinge of inadequacy), he used his penis to prop himself up (as in the photo), swat flies from his side and scratch himself on his stomach. David Attenborough never showed us that…
There’s good reason for elephants to have prehensile penises. It’s hard enough for a six-tonne animal to get into the right position for sex, let alone having to do the rhythmic thrusting that’s required. So he let’s his penis do all the work for him.
You’ll also note the dark stain behind his eye – that’s a leak from his temporal gland. It means that this male was entering musth, the period when their testosterone shoots through the roof and they get incredibly horny and aggressive. We tried to drive round this male and he basically charged us. Tramply doom was averted by our driver who slammed his palm against the car door as hard as he could. The elephant stopped and huffed and puffed. We did our best to not soil ourselves.
This picture gives you an idea of how close he was. After a seemingly infinite standstill, he moved aside, extended his enormous penis and had a wee. It’s amazing how terror can convert into comedy so quickly…
We had numerous elephant sightings on our South Africa trip including a few family groups and a couple of lone males. Seeing them in documentaries or in zoos never quite captures just how big and impressive they are in the flesh, especially when they do things like beat up a tree. Note how this male uses his tusks and trunks to break off branches.
Also note how quiet it is except for the breaking of branches. Elephants may look like lumbering beasts, but their footfalls are dainty and quiet. They are ‘digitigrade’, meaning that they walk on their toes like a cat or a dog. Their heels rest on a spongy cushion that gives their foot its flat, round appearance – they’ve essentially got the world’s largest platform shoes. And that means that walking elephants make precious little noise. You could watch a group disappear behind a bush about 10 metres away and have absolutely no idea that they were there.