The latest episode of the Eons podcast is a special Q&A
episode featuring all three Eons hosts and special guest Hank Green!
Blake, Michelle, Hank, and I discussed a bunch of things that y’all have been
curious about including why studying deep time matters and more serious questions
like “Did dinosaurs taste like chicken?” Check it out now wherever you get your podcasts!
Of all the charismatic, giant animals that roamed the planet during the last ice age,
the most iconic may have been the woolly mammoths.
Massive, powerful, and capable of surviving temperatures as low as 40 degrees below zero,
they ranged from Western Europe through Russia and into North America.
But despite being so well-adapted to extreme cold, they were rather recent arrivals to the northern
hemisphere - the result of great migrations from much warmer, southern environments.
Some of the adaptations that allowed them to thrive in the icy north were pretty obvious,
while others were invisible, but no less important.
And figuring out exactly what those adaptations were has been a truly
mammoth challenge - and one that has revealed many surprises.
Because, it turns out that, in the quest to understand how evolution basically
built the woolly mammoth, we may have found the blueprints for building them ourselves.
The fossil record of woolly mammoths tells us that their ancestors migrated to northern Eurasia
around 2.5 million years ago, and eventually North America about 1.5 million years ago.
Before that, they lived in Africa. And there, around 5 million years ago,
the first mammoths evolved.
Now, those early mammoths would’ve been adapted for shedding heat, rather than retaining it.
So they probably had some traits in common with today’s elephants… like not having any fur,
for example, and having their famously big ears, which helped dissipate heat.
But when mammoths left their home in Africa and ventured into Eurasia,
they encountered a new set of environmental pressures.
Over the course of the next two million years or so,
through the early and middle parts of the Pleistocene epoch,
they radiated into a succession of mammoth species, often overlapping in time and space.
And one of these species, called the Steppe mammoth,
eventually gave rise to the woolly mammoth, around 700,000 years ago.
Their thick, insulating coats and smaller ears
were two of the obvious adaptations they had for coping with the cold.
But they’d also picked up other, invisible adaptations on their
evolutionary journey - ones that can only be seen by studying their DNA.
In 2010, for example, researchers were able to isolate the woolly mammoth genes that code
for hemoglobin - the protein in red blood cells that carries oxygen around the body.
Identifying these genes allowed scientists to actually synthesize
woolly mammoth hemoglobin in the lab.
And by comparing it to the hemoglobin of modern elephants,
they found that the mammoth’s version had picked up some structural changes
that allowed it to function much more efficiently at colder temperatures.
Then, in 2015, a team of researchers went a step further. Instead of isolating individual genes,
they studied whole woolly mammoth genomes.
They sequenced the ancient DNA of two woolly mammoths, both from Siberia,
one dating to 20,000 years ago and the other to 60,000 years ago.
After piecing together as much of each genome as possible,
the researchers compared them to the genomes of Asian elephants - their closest living relatives.
And it turns out, the woolly mammoths had changes to more than 1600 genes – many of
them associated with traits that made the mammoths more likely to survive in the cold.
For example, lots of variants were in genes associated with hair development,
and more than 50 were found in genes involved with adipose tissue - aka fat.
These probably contributed to the mammoths having
thicker and more widespread fat deposits … which helped them conserve heat and store energy.
And eight of the genes were involved with the circadian system - the internal clock that
syncs the body’s biology and behavior with daily cycles of day and night.
At high latitudes, the cycles of light and dark swing between seasonal extremes - with long,
dark winters and summers of near-constant daylight.
So it makes sense that this system would’ve changed over time to help mammoths survive
in their Arctic range – affecting their patterns of sleeping, eating, socializing, metabolizing,
and all of the other things that are coordinated by the circadian rhythm.
But one of the most intriguing changes was in an ancient gene called TRPV3,
which is common to a lot of vertebrates.
This single gene affects multiple traits, including sensing temperatures,
hair growth, and the formation of fat tissues.
For example, studies have found that when this gene is turned off in mice,
the mice prefer colder temperatures. And they grow longer, wavier hair …
In woolly mammoths, this gene still worked,
but the protein it produced was much less active compared to the elephant’s version.
So dialing down the activity of this one gene
may have contributed to several of the woolly mammoths’ most impressive
adaptations - including their cold tolerance, increased fat formation, and distinctive coat.
Now, while all of these studies seem like they’re only useful for looking into the
woolly mammoths’ past, they might actually have implications for their future as well.
Because, the basic question at the heart of this research is:
what makes a woolly mammoth a woolly mammoth?
If we can identify the genes responsible for their distinct features – and where they differ from
their living and extinct relatives – it might give us a blueprint for woolly mammoth de-extinction.
Now de-extinction is the process of resurrecting an extinct species - either by bringing it back
just as it was or by creating an organism that closely resembles it physically and ecologically.
And while the idea of resurrecting woolly mammoths has captured peoples’ imagination for a long time,
it's only recently that we’ve begun to understand their genetics enough
to work out how it could actually be done.
Because all of this research has essentially given us an incomplete list
of the genetic changes that separate a woolly mammoth from an Asian elephant.
And the rise of gene-editing technology has made it at least theoretically possible that
some of those changes could be edited into the embryo of an Asian elephant.
Now, the result wouldn’t be a true woolly mammoth,
but more like a partially mammoth-ized, cold-adapted Asian elephant.
Depending on which of its genes were tweaked to resemble those of a mammoth,
it might have some of their typical traits, like woolliness, more fat deposits,
cold-tolerant hemoglobin, and a circadian system suited to the Arctic.
But, that’s assuming those genes are actually connected to those traits.
Their actual contributions to complex traits in mammoths might
be messier than we realize or can predict ahead of time in the lab.
And then there’s another problem. To paraphrase the great Dr. Ian Malcolm,
We might become so preoccupied with whether we could, that we don’t stop to think if we should.
After all, there are many ethical concerns around doing this kind of work
on such highly intelligent and deeply social endangered animals.
Plus, the environments they lived in have changed a lot since their heyday in the Late Pleistocene.
Like, the planet is a lot warmer now and is getting warmer still.
So even if we could create animals that resembled woolly mammoths, and give them a habitat like the
arctic tundra they once roamed, we have to ask, would that be a sensible thing to do?
Or would we just be trying to imitate a world that’s long gone?
That question is the elephant in the room.
Did you know mammoths were still around when the Great Pyramids were built?
Check out our episode, “The Island of the Last Surviving Mammoths” for more information.
And we /woolly/ gotta thank this month’s Eontologists!
Annie & Eric Higgins, Chase Archambault (R-sham-bow), Colton, Jake Hart,
John Davison Ng, Melanie Lam Carnevale (karr-nuh-vayl), and Yanshuo Li (yan-show lee)
By becoming an Eonite at patreon.com/eons, you can get fun perks like submitting a joke for us
to read, like this one from Hosni Why do Pteranodons got a P?
Same reason as us, they would explode otherwise.
And as always thank you for joining me in the Adam Lowe studio.
Subscribe at youtube.com/eons for more evolutionary escapades!