Which extinct animals could be cloned right now?

photo by Nancy Steffens

This question draws forth images of children heading off to school each morning, riding on their saber-tooth cats, pet moas stalking along behind, dodging roaming mammoths along their way.

What is cloning, really?

Cloning is a process that makes genetically identical copies of an organism.  There is such a thing as natural cloning – this occurs with some plants and single-cell organisms which copy themselves without fertilization, and identical twins are also natural clones.  As for artificial cloning, there are three basic types – gene, therapeutic and reproductive.

Gene cloning makes copies of genes or DNA, and therapeutic cloning makes stem cells for creating new tissues.  But here we’ll be talking about reproductive cloning -- the method by which an animal can be created from material cells, such as those from skin and hair. 

The basic process is this: an egg is taken from a living animal and the cell’s nucleus is removed.  To review, the nucleus is where the DNA hangs out, which instructs the cell as to what to do with itself.  Then a cell is taken from the animal to be cloned, and its nucleus is removed and put into the host egg.  This is done either by just sucking it out with a syringe and inserting it into the egg, or by joining the two with an electric pulse.

Now you have a living animal’s egg containing a nucleus from another (could be dead) animal.  The egg is spurred into action with electricity, and after it grows to embryo size in a lab, it is placed into the womb of a related species. 

There’s a handy illustrated fact sheet about the process here.

Now you could have a kitten growing in Cat C that came from the egg of Cat B and a skin cell of Cat A.  Or a saber-tooth baby going for a ride in a lion.  Or even a Tasmanian tiger, the genes of which have been made to be produced in the fetus of a mouse -- not that the mouse in this case carried a tiger to term, but it illustrates that you don’t need to have the same kind of animal to recreate age-old genes.  Surrogate mothers for full-term, fully-formed creatures should, however, be at least somewhat related to the original species.

So thanks to the existence of elephants, we could find a surrogate mother for a mammoth, and recreating the passenger pigeon via a rock pigeon’s egg would be easy (as easy as cloning is, that is.)  But the lack of availability of a suitable womb would postpone the de-extinction of some species, notably the giant ground sloth, which will have to wait for an artificial womb because its closest living relative – the 8-kg two-toed sloth – would have a mighty hard time birthing a 1,000-kg ground sloth baby.

As for animals that have no existing relatives, there is still hope.  As recently as 2007, a method was found for reverting adult cells into embryo-like stem cells, which could then be made to produce any kind of tissue call.  So finding an egg to host is not necessarily necessary, but the technology still has a ways to go before it becomes particularly efficient.

Does it work?

Most of the time, actually, no.  Cloning has a very low success rate compared with good ol’ regular reproduction.  The first animal successfully cloned from an adult cell – the famous Dolly the sheep, born in 1996 – followed 276 failed attempts. 

While cloning from adult cells of living creatures has gradually gotten more successful, the overall baby production process is still way less efficient than letting the animals reproduce naturally, not to mention that clones have a higher propensity for health problems than non-clones. 

So as far as, say, producing livestock, cloning makes no sense.  But in the case of extinct animals, it is the only way.

So whose DNA do we actually have available to clone right now?

Creatures that died off more than a few tens of thousands of years ago are gone for good; their DNA has broken down by now.  However, animals that have gone extinct during or after the last ice age stand a chance if some of their tissue was preserved.  Ice-age creatures have been found preserved in -- no surprise -- ice, as well as tar pits, and animals that died more recently have been collected by curators of museums and labs.

The San Diego’s FrozenZoo has cells from over 1,000 different species, including critically endangered species like the northern white rhino.  Around the globe, cells are on hand that could possibly be reborn into a number of extinct species, including the recently extinct Tasmanian tiger and passenger pigeon, the giant moa, the Irish elk, and yes, saber-tooth cats and mammoths.

Also in the lineup for de-extinctable species are – ready for this? – Neanderthals.  Recent evidence has suggested that those beefy cave-dwellers were actually much more intelligent and articulate than previously believed, and it turns out that they’re not so separate of a species from us after all.  In fact, interbreeding certainly occurred, and still does, sort of – it so happens that a lot of us have Neanderthal DNA in us right now!  My own uncle recently got confirmation that he’s 2% Neanderthal, so I guess I’m in the club.  Does that explain why I lumber around so much before I get coffee?

 

Has anyone brought an extinct species back?

Yes, indeed – but sadly, not for long.  In 2003, scientists cloned a Pyrenean Ibex, the first to exist on Earth since the species’ presumed extinction in 1999.   Unfortunately, the youngster died soon after birth from a malformation in its lungs.

Still, hope is in the air, and plans are ever afoot to clone lost creatures, especially the iconic mammoth.  Japan’s Dr. Akira Iritani claims he will produce a mammoth by 2016…which is pretty optimistic, considering the general failure rate and the fact that the critter will have to gestate for a good year and a half at least.

It seemed like a good idea at the time

So should we really be doing this?

When faced with the question of whether the dinosaurs in the movie Jurassic Park should exist, Jeff Goldblum’s character Dr. Malcolm says, “Your scientists were so preoccupied with whether or not they could that they didn't stop to think if they should!”

There are those who believe that we owe resurrection to creatures that humans drove to extinction.  This excerpt from a NationalGeographic article shows the stance nicely:

“If we’re talking about species we drove extinct, then I think we have an obligation to try to do this,” says Michael Archer, a paleontologist at the University of New South Wales who has championed de-extinction for years. Some people protest that reviving a species that no longer exists amounts to playing God. Archer scoffs at the notion. “I think we played God when we exterminated these animals.”

There is also the belief that we should carry on with cloning because, well, we can.  As Insung Hwang of the Sooam Biotech Research Foundation says, “The thing that I always say is, if you don’t try, how would you know that it’s impossible?”

Some reasons to reconsider just up and cloning everything include concern about the survival of the animals once they’re back on Earth.  For some species, their former habitat is greatly reduced or entirely unavailable.  Alternately, some species whose habitat is intact may pose a threat to the ecosystem that has established itself since the animals’ departure, making the extinct species now an invasive one.

Others believe that resources would be better spent focused on the preservation of existing endangered species.  Cash goes a lot further in environmental preservation efforts than it does in the realm of low-success-rate cloning.  Proponents of the focus-on-the-now crowd also see cloning as better used to preserve tissues and attempt to clone living endangered animals before working on those that are already extinct.

The seven-year-old who brought up this question thinks that science should certainly try to clone some extinct species, but cautions against reviving the “dangerous” species of the past.  “Wooly mammoths could be stomping on and destroying everything…and saber-tooth tigers would do damage to alive creatures.”  I can see some wisdom in that.

Truth, bro.

But really, pros and cons aside, wouldn’t it just be neat to see some ice age megafauna cruising around in the flesh?  Hank Greely, a leading bioethicist at Stanford University, agrees:

“What intrigues me is just that it’s really cool,” Greely says. “A saber-toothed cat?  It would be neat to see one of those.”

Especially if we could ride it to school.