活着的野生物种就像装满未读书本的图书馆……破坏它们就等于烧毁那个图书馆—— John Dingell
In the savannahs of Kenya, two female northern white rhinos
Nájin and Fatu, munch contentedly on the grass.
At the time of this video’s publication,
these are the last two known northern white rhinos left on Earth.
Their species is functionally extinct–
without a male, Nájin and Fatu can’t reproduce.
And yet, there’s still hope to revive the northern white rhino.
How can that be?
The story starts about 50 years ago,
when poachers began illegally hunting thousands of rhinos
across Africa for their horns.
This, combined with civil wars in their territory,
decimated northern white rhino populations.
Concerned conservationists began trying to breed them in
captivity in the 1970s,
collecting and storing semen from males.
Only four rhinos were ultimately born through the ambitious breeding program.
Nájin, and her daughter Fatu were the last two.
In 2014, conservationists discovered that neither can have a calf.
Though Nájin gave birth to Fatu, she now has weak hindlegs,
which could harm her health if she became pregnant again.
Fatu, meanwhile, has a degenerated uterine lining.
Then, the last northern white rhino male of the species, Sudan,
died in 2018.
But there was one glimmer of hope: artificial reproduction.
With no living males and no females able to carry a pregnancy,
this is a complicated and risky process to say the least.
Though scientists had stored semen, they would have to collect the eggs—
a complex procedure that requires a female to be sedated for up to two hours.
Then, they’d create a viable embryo in the lab–
something that had never been done before, and no one knew how to do.
Even that was just the beginning–
a surrogate mother of another rhino species
would have to carry the embryo to term.
Females of a closely related species, the southern white rhino,
became both the key to developing a rhino embryo in a lab
and the leading candidates for surrogate mothers.
Northern and southern white rhinos diverged about a million of years ago
into separate— though still closely-related— species.
They inhabit different regions, and have slightly different physical traits.
In a fortunate coincidence, several female southern white rhinos
needed treatment for their own reproductive problems,
and researchers could collect eggs as part of that treatment.
In Dvůr Králové Zoo in October 2015,
2015年十月 在Dvůr Králové动物园
experts of IZW Berlin began collecting eggs from southern white rhinos
and sending them to Avantea, an animal reproduction laboratory in Italy.
并送到意大利一个动物繁殖实验室 —— Avantea
There, scientists developed and perfected a technique
to create a viable embryo.
Once they mastered the technique,
researchers extracted Nájin and Fatu’s eggs
on August 22, 2019
and flew them to Italy.
Three days later, they fertilized the eggs with sperm
from a northern white rhino male.
After another week, two of the eggs made it to the stage of development
when the embryo can be frozen and preserved for future.
Another collection in December 2019 produced one more embryo.
As of early 2020, the plan is to collect Nájin and Fatu’s eggs
three times a year if they’re healthy enough.
In the meantime, researchers are looking for
promising southern white rhino surrogate mothers–
ideally who’ve carried a pregnancy to term before.
The surrogacy plan is somewhat of a leap of faith–
southern and northern white rhinos have interbred
both during the last glacial period and more recently in 1977,
so researchers are optimistic a southern white rhino
would be able to carry a northern white rhino to term.
Also, the two species’ pregnancies are the same length.
Still, transferring an embryo to a rhino is tricky
because of the shape of the cervix.
The ultimate goal, which will take decades,
is to establish a breeding population of northern white rhinos
in their original range.
Studies suggest that we have samples from enough individuals
to recreate a population with the genetic diversity the species had a century ago.
Though the specifics of this effort are unique,
as more species face critical endangerment or functional extinction,
it’s also an arena for big questions:
do we have a responsibility to try to bring species back from the brink,
especially when human actions brought them there in the first place?
Are there limits to the effort we should expend
on saving animals threatened with extinction?