From the Vault: Carl Zimmer on Heredity's Power

Why does heredity hold such power over us? How did the ancients contemplate it and how is genetic technology changing the shape of future heredity? In this classic episode, Robert and Joe chat with acclaimed science writer Carl Zimmer about the topics explored in his  book “She Has Her Mother's Laugh: The Powers, Perversions, and Potential of Heredity.” (Originally published June 14, 2018)

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Episode Transcript

Speaker 1 (00:05):
Hey, you welcome to Stuff to Blow your mind. My
name is Robert Lamb and I'm Joe McCormick, and it's Saturday.
Time to go into the Old Vault. This time we're
going in for an interview. I want to say that
this was a really interesting interview. I really liked it.
This is the interview we had with the science writer
Carl Zimmer, originally published in June of about his book

(00:26):
on heredity called She Has Her Mother's Laugh The Powers,
Perversions and Potential of Heredity. And I thought this was
a really good talk. Yeah, this was a lot of fun.
You know, I just got him chatting about, you know,
his experiences writing the book, uh, you know, some of
the real you know, high points regarding like what heredity is,
how it works, and and also I remember we got

(00:48):
him talking a little bit about like okay, what if
what if you were to write your name and someone's genes,
Like how long would that signature last? Uh So, yeah,
it's a fun conversation and uh, you know it was
and it was on honor to get to talk to
Carl Zimmer, who's, you know, such a big name in
science communication. He's been one of my favorite science writers
for years and it was really cool. All right, let's

(01:09):
jump right in. Welcome to Stuff to Blow your Mind
from how Stuff Works dot com. Hey you, welcome to
Stuff to Blow your Mind. My name is Robert Lamb
and I'm Joe McCormick. And boy, do we have a
treat for you today. That's right, we're we're chatting with

(01:30):
Carl Zimmer about his new book, She Has Her Mother's Laugh,
The Powers, Perversions and Potential of Heredity. This is a
fantastic book. I was trying to finish it before we
talked to him today, and I was up till two
am last night and getting to the very last page.
But it was worth it. It is a great book.
I really highly recommended. It's a brick that's just full

(01:52):
of weird, interesting delights and insights about how our views
of heredity have changed over the years, all of the
good and all of the evil to that knowledge has
been used for and uh and also where it's going
in the future. Yeah, yeah, this it's a fascinating book.
I also I got to see him in conversation with
the Maria Knakova at World Science Festival this year, in

(02:14):
which he talked about the themes in the book as well,
So it was a real it's a real delight to
have him here on the show. And if you want
to check out She Has Her Mother's Laugh. It is
available in hardback, digital and as an audio book. So, uh,
we hope you enjoy our interview with him, but certainly
go check out his book as well for just an

(02:34):
in depth, riveting journey through heredity. Now, wait a minute,
we should say who he is. I don't think we've
done that if you're if you're not familiar with Carl
Zimmer and Carl Carl Zimmer is a prolific, excellent science writer.
He writes for the New York Times. I think I've
also seen these articles in the Atlantic and National Geographic
all over the place. Uh. He's written a lot about
parasites and uh, some of the most interesting stuff in

(02:57):
biology is is Karl's territory. And uh, and I really
had a good time talking to him today. Yes, some
of his past books include Parasite rex Evolution, The Triumph
of an Idea, and Microcosm. So, without further ado, here's
our conversation with Carl Zimmer. So, Carl, what led you
to write a book about heredity. I guess in a way,

(03:19):
I've been thinking about heredity for forever. Really. I mean,
I when I was a kid, you know, I would
uh think back on my ancestors that my parents told
me about, and you know, I wonder like, oh wow,
if if you know, Roger Goodspeed had not sailed from
England to Massachusetts in the sixteen thirties, would I ever exist?

(03:43):
You know, those sorts of things. And then when I
became a father, I've got two teenage girls now, and
you know that immediately brought to bear just how urgent
and mysterious heredity can be. Because now they these two
people walking around who have inherited a lot of my genes,

(04:04):
and you know what, what is it that I'm giving
them that that suddenly becomes a very pressing issue. And
I guess what really then kind of crystallize it all
for me, was that in the past few years, I've
been doing a lot of reporting from the New York
Times and elsewhere about the real revolution happening in biology,

(04:25):
allowing scientists to sequenced DNA, to rewrite DNA, and to
also look at other kinds of biology that might help
uh create this thing that we call heredity. Uh, and
so it just it all kind of came together, and
I realized that this would be something that I really

(04:45):
wanted to spend a couple of years really exploring deeply.
So you mentioned the idea of the sort of personal
curiosity about our ancestors, and you talk in the book
about how we often do family genealogies to sort of
learn something about ourselves, as if the seeds of who
we are are somehow present in our really distant ancestors.

(05:06):
But how many generations back do you have to go
before those relationships with our ancestors really don't matter all
that much in terms of genetic closeness. You know, you
don't have to go back that far. And that just
has to do with how parents passed down their DNA
to their kids. You know, we each have two copies

(05:27):
of each gene for the most part, but you know,
parents only passed down one copy of a given gene
to each child. And so if you repeat that process
generation after generation, there's a sort of a kind of
a stochastic, kind of random process that will basically lead

(05:47):
to you know, uh, some descendants not having any DNA
at all from a particular ancestor. Um, there's only so
much room in your genome and you can't pack in
all the DNA for all your ancestors basically, and so
geneticis have done some back of the envelope calculations and
if you go back let's say ten generations, um, that

(06:10):
would be like your ancestors in the sixt dreds. Uh,
maybe only about half of them have a genetic link
to you. The rest they're still your ancestors. But you
cannot point to any piece of DNA in your genome
and say, oh, I got that from from this particular
person you know. So Um, So I think that actually

(06:30):
like really shows how we have to, um think think
bigger when it comes to heredity. It's not just some
particular bit of DNA that that gives heredity its meaning. Well,
on the other side of that coin, UM, could you
talk a little bit about what the Yale mathematician Joseph
Chang discovered about human ancestry. It seems sort of like

(06:51):
the flip side of what you're just talking about. Yeah,
I mean, so you know, so much about heredity is
counterintuitive and almost you know, it seems to contradict itself.
And that's in a way what makes it so fascinating.
So I just told you about how if you go
back a certain number of generations, you're gonna encounter ancestors
from whom you've inherited no DNA at all. Um. But

(07:15):
there's an interesting feature of human ancestry, which is that, um,
you know people uh, everybody today, Uh, you know, it
shares a common ancestor with some people who lived about
five thousand years ago, roughly speaking in other words, UM,

(07:37):
if you, if you, it's just a you can and
you can figure this out as just changed just by
looking at Genealogy is a mathematical problem. Um, just think
of think of our genealogy is a kind of a
branching network. Um. The thing is though that uh you
know are if you think about your family tree, um,

(07:59):
and you think while as me, and then you branch
off to your parents, and then they branch off to
their parents and so on and so forth. Um. If
you just keep branching in that simple way, you're gonna
end up, you know, a few thousand years back with
more ancestors than there are people who have ever lived.
You know, we're talking chillions of people. And that's absurd.
So so that's actually not a realistic model of your ancestry.

(08:23):
The fact is that your aunt all of you know,
your parents are cousins. Now either that you know, in
some cases first cousins get married, but in other cases
they're very distant cousins. Another what that means is that
your parents share an ancestor, a common ancestor somewhere in
the past. It could be hundreds of thousands of years ago,

(08:46):
but it doesn't matter. They have an ancestor. So what
that does is it folds the family tree back in
on itself. And what Joseph Chang realized was that that
actually does something very interesting to human ancestry. What it
means is that you do not have to go back
very far to find somebody who is the common ancestor

(09:07):
of literally everyone on earth. Uh And it's just in
the past few thousand years that you could find people
like that. Um. Now, of course you know those common ancestors,
you know they for each of us that that that's
one person or a few people out of thousands upon
thousands of ancestors. But it's something that ties us all together.

(09:31):
And the irony is that you know, people are really
uh uh, really love to connect themselves to someone famous.
You know, like, oh, did you know that I am
descended from William the Conqueror? And the fact is that
probably probably everybody of European descent is and is a
descendant of William the Conqueror. Probably everybody of European descent

(09:56):
is a descendant of Charlemagne Um. And you know, it's
possible that everybody on earth is a descendant of you know,
maybe Cleopatra. It's like, that's just the nature of human
genealogy is that it's we're all descended from kings. That
doesn't make anybody special. Well as as long as we're

(10:20):
gazing backwards in time, here, can you tell us how
ancient thinkers contemplated heredity? The weird thing is that they
really didn't. And they at least they didn't think about
heredity in the way that we do. Uh. You know,
if you go back and you you look at what
Hippocrates would say or Aristottle would say, Uh, this, this

(10:42):
whole model of how we inherit something you know, microscopic
and biological that that determines how we ended up the
way we are just would not compute for them. And so,
you know, you know, someone like Aristotle would say like, well,
you know, the thing that one generation looks like the
previous one is just because it's the same chemistry. Um,

(11:04):
you know, of course you're going to be the uh,
you're going to be the same because you know, it's
the same set of processes that produced a person that
produced you. So what's the big deal? And you know
the word heredity, You know, it's a very old word,
but it only referred to basically inheriting stuff. Um, you know,

(11:25):
and I'm talking not talking about jeanes, I'm talking about houses, uh,
you know, farmland things like that. You know, So in
the Roman Empire there are lots of rules about you know,
who got to be an heir, and that's what the
word meant at that point. And it's really fascinating, Like
you have to you have to wait a long time
before you start to even see the first glimmers of
how we think about heredity today. Um. My favorite example

(11:48):
is in the fifteen fifteen, around fifteen eighty, uh, Montana
this this famous essays. He writes an essay about his
father because Mathenniel now is starting to get older and
he's developing kidney stones, and it occurs to him that
his father had kidney stones and around the same age,

(12:10):
and he basically writes success saying, well, what is up
with that? Now? Did I get these kid stones from
my father? And like, if so, how because you know,
when I was born, my father was young and he
didn't have kidney stones, So what exactly went from him
to me? Um? And you want to just you know,

(12:31):
shout at the page like it's it's jeans, it's jeans.
But you know he can't hear you, you know, like
he his question went fundamentally unanswered for centuries. Um And
so yeah, so so uh, it's really need to look
back and and see how. You know, the way we
think is not how everyone always thought. You know, the

(12:53):
way we think about heredity is is a product of
really the modern age. So did the select the breeding
of animals and plants inform classical and medieval thinkers at
all about the possible nature of heredity, because it seems
it's I mean, it's kind of seems like people such
as Aristotle or Albertus Magnus would have would have looked
at how we bred flowers, crops and farm animals more

(13:15):
were at least in addition to the influence of geography
or experience, you would think so, I would I would
have thought so. But I think that's because we are
in the century and we look back and say, well,
everyone must have thought the way we did. But there
are actually, you know, whole books written, uh you know
by Roman writers about farming for example, UM, and you

(13:36):
can search them as I mean, I have sat down
and look through these books for anything resembling what you're
talking about, and it's just not there. They do not
talk about, oh, well, there's some you know quality in
this particular variety of olives that you know, if you
if you, if you breed it, it will pass it

(13:57):
down to two future generations of olive trees. That this
isn't there. Instead, they'll say like, well, make sure that
you know you're you're growing it on good soil, make
sure your your farm gets a good supply rain. It's
all about the environment. And it isn't really until I

(14:18):
would argue, it's not really until the seventeen hundreds that uh,
you start to see these farmers, these livestock breeders really
take interest in this um. And part of it is
that these European countries are all um looking for ways
to use science to uh make their countries wealthier. And

(14:45):
you know they're thinking, well, if we can we can,
if we can produce new varieties of animals implants, um,
then we we will enrich ourselves. Uh. And there's this
one breeder named Robert Bakewell who produces an entirely new
eat of sheep just by starting to think about heredity,

(15:05):
to think about which individuals those sheep is he gonna
mate together? Is he gonna just only mate within his flock?
Is he gonna go pick out other ones from other
flocks to mate? Um? And lo and behold he produces
this this very successful new breed. And you know, people
like Charles Darwin look at that and say, what has happened?
How did they do that? Um? And in Germany and

(15:27):
in Central Europe there's a big push to do the
same thing with sheep, to do that with crops as well,
and uh and to try to understand what are these rules.
And one of those people who's trying to understand those
rules is none other than Gregor mendel Um. So his
his breeding experiments. You know, the foundation of genetics comes

(15:48):
out of this new push to try to use heredity
to enrich nations. All Right, we're gonna take a quick
break and then we're gonna jump right back in to
the interview and we're back. So at what point does
the modern idea of heredity really emerge. Well, I'd say

(16:09):
in the late eighteen hundreds, UM, people start to talk
about heredity as a scientific question. And Charles Darwin is
really important in all of this because, you know, he
comes up with this theory of evolution and it depends
on heredity. In other words, Um, you know, the only
way for natural selection to work is so if parents

(16:31):
can pass down traits to their offspring to give them
some advantage and surviving and reproducing. And so it's very
obvious to Darwin that, you know that that heredity is
this huge glaring question in the middle of his theory,
and he and he works really hard to try to
find out for himself how heredity works. And he's very

(16:53):
aware of a lot of the research that's going on
at the time looking to the discovery of cells and
the discovery that there are a little things inside of cells,
but no one's quite sure what they are, UM. And
so he developed a theory that there are particles in
the cells throughout our body that they somehow stream into
the eggs and sperm and uh then become something like

(17:16):
we the way we think of genes um. That doesn't
pan out. You know, his cousin Francis Galton, tries to
test it by injecting blood from uh, you know, black
rabbits into white rabbits, you know, different colored rabbits, and
seeing if that changes the color of their offspring. Doesn't happen.
Uh and uh So it's not really until after Darwin

(17:39):
is dead that scientists start to really understand chromosomes and
then rediscover mental and it all clicks together, and the
science that they that they call genetics is born in
nineteen uh and and you know, the it's really you
can see how exciting it is for the scientists at

(18:01):
the time. William Bateson, who coined the term genetics, he
writes at the time that you know, the science of
heredity has been revolutionized. You know that finally they feel
like they can they can understand heredity um in its
fundamental basis. So so how do we go from this
point of of of just excitement and discovery and just

(18:22):
fall so steeply into eugenics and then ultimately the horrors
of the Third Reich. Well, if you look back, the
roots of eugenics UM go back pretty far. Um. You
know so Uh. On the one hand, Uh, so our
modern conception of race UH starts to develop as early

(18:46):
as really the fifteen hundreds are the fourteen hundreds, even
where in Spain, uh, Jews are are being considered a
separate race of people, and and and noble families have
to do have to draw out genealogies to prove that
they don't have any Jews in their in their ancestry. Um.

(19:09):
Otherwise they you know, they won't be able to get
that good job in government or so on. And so
that starts to develop this idea that that groups of
people are fundamentally different in some way that is carried
on from one generation to the next. Um. Then Uh,
in the in the eighteen hundreds, you start to see,

(19:30):
you know, a real concern about UM poverty and crime,
and and a lot of people start to to make
claims that these are being carried down in certain families.
You know, there are these bad families and why is
it that one generation is just as bad as the
previous one. And you know, people talk about some sort

(19:52):
of hereditary curse that they must have. And and then
you know, how do we keep that curse from being propagated? Okay?
And so then when genetics gets discovered, um, a lot
of actual genesis themselves and uh and other and others
say well, aha, like here's here's the basis for what

(20:13):
we've been talking about for decades now. Um. And you know,
the word eugenics had actually been coined in eighteen eighties
by Francis Coulton, Uh, Darwin's cousin, and he just thought, well,
you know, if intelligence is inherited, then why don't we
just essentially breed people away we breed sheep, So you
just pick out the individuals who seemed to have, you know,

(20:36):
the most genius he would call it, and then encourage
them to have lots of kids. And and he had
these dreams that to produced what he called the galaxy
of genius in the future. Um. But by the time
that eugenics arrives in the United States and genetics emerges,
it takes on a much darker cast because people say, well,

(20:57):
what we really need to focus on is as these
people who have who we believe have genes that we
don't like, and we want to prevent them from reproducing,
because that's going to drag down our country, and so
what are we going to do to keep them from reproducing?
And um, that leads to sterilization and much worse. So,
in reading your chapter about Henry Goddard and the origins

(21:21):
of the American eugenics movement, I'm struck that this is
a potential example of the dangers of bad research. Like
you draw a really disturbing picture of how but like
sloppy or fraudulent work that became the basis of Henry
Goddard's published writings on heredity can be viewed in some
ways is contributing directly to real world consequences, like the

(21:43):
horrors of for sterilization in the United States or mass
murder in Europe. Do you ever think, when you see
bad science or pseudoscience being being publicized today that it
could ever lead to such nightmares that even its authors
might not have imagined? Uh, you know, I don't. I
think that we can't uh rule out those kinds of possibilities.

(22:07):
I mean, it might be very, very unlikely, but I mean,
if you look at history, you can see how bad
science combined with existing prejudices led to really horrific outcomes.
And it wasn't that the science was somehow appropriated by

(22:28):
pseudo scientists or something. Uh. Eugenics was embraced by most
of the leading um biologists of the time. Uh and Uh,
there were different forms of eugenics, you know. So some
people were very much sort of concerned. We were quite
racist and you know, concerned about uh, you know, the

(22:51):
white quote unquote race being you know, polluted by other races. Um.
But then there were progressives who thought that this was
going to be part of their grand plan for making
society a better, fairer place. Um. And I think it's
really important to look at these episodes in history to

(23:13):
see how things go bad. Um. And I think it's
I think it's arrogant for any of us to say, well,
things like this could never happen again, you know, and
somehow we're vaccinated from from these sorts of things. But
we can draw lessons from the past, and we can
see how, um, how humble we need to be in

(23:33):
the face of complexity in in our own biology. You know.
We you know, I think we're in like in another revolution,
the way we were a hundred years ago, you know,
a hundred years ago, genetics itself was profoundly new. That
gene was a new thing. Uh. Now we're at the
point where we're looking at genomes, in other words, all

(23:54):
the genes in our in our selves, and we can
we can see them down to the atomic detail. UM,
but there's still a vast amount we do not understand
about it, and UM, you know, we we cannot let
that be an opportunity to uh, you know, card out
our old biases and prejudices and say, oh, I see

(24:17):
now science backs up what I was saying all along
about those other people. UM, we can't. We just we
cannot let that happen again. I think that's a really
good point. And I also think you can even look
at it as there's a flip side to it where
modern discoveries of genomics really complicate or in some sense

(24:37):
is undermine what many people have traditionally understood as the
concept of race within humans. Right. Yeah, So the scientific
concept of race UH developed in in the seventeen hundreds,
and it was really UM very much spurred on by
UH by what Europe was doing at the time. So

(25:01):
Europe was in the midst of building up huge colonies
UM and enslaving many many people. There was a need
for sort of legal and moral justifications for doing this,
and a lot of it, uh was based on these
concepts of race, so that for example, you know, Africans

(25:21):
were were claimed to be a completely separate race, uh
that you know, had inherent uh inferiority to the white race.
And so therefore slavery is okay. And you can see
this again and again in in lots of lots of
writing at the time. Uh. Now, even in the early

(25:44):
nineteen hundreds, Um, there were there were indications that this
kind that genetics was not aligning with these these uh
old ideas about race. They just weren't fitting neatly. Um.
You it was very it was it was becoming harder
and harder to sort of draw any particularly bright line

(26:07):
between groups of people. I mean, obviously people are different, uh.
You know, there are lots of differences and people in
terms of skin color and height and shapes of faces
and culture and all the rest of it. But the
genes were not supporting these old ideas about race. And
by the midnighteteen hundreds of people, a lot of anthropologists
and geneticisis we're saying, you know, the word race is

(26:31):
so burdened with so much that's terrible and immoral and
has so little connection with the way we're starting to
understand populations. Let's just get abandoned it. Um, that really
hasn't that really didn't happen. But nevertheless, like now where
we can look at whole genomes. Um. Yeah, the whole

(26:53):
thing with race now is is it just is it's
a bit one. The way one Jenet has put it
to me is, well, you know, like talking for us,
like talking about races, like the way Greeks talked about
the you know, the four elements, air, fire, water, earth,
like you know it. You know, Aristotle could explain all

(27:13):
sorts of things, uh that way, and they seemed good
to him. But you know, we know that there's things
are much more complex than the four elements, and if
you forced physicists to go back to the four elements,
they'd be very unhappy. So genets are saying, like, please
don't make us go back to you know, the genetic
equivalent of the four elements. You know, we're you know,

(27:34):
they're very interested in ancestry and how populations mixed together,
how they become isolated, and all the rest of it.
But these old ideas about race and on all the
connotations of race, they don't map onto it at all,
so they just don't want to use it now. Of course,
in addition to just the passing on of genetic information, UH,
we also have epigenetics. And even as you explore the

(27:57):
effects of the microbiome, can can you talk about how
these if changed our definition of heredity. So in the
eight hundreds, heredity becomes a scientific question. You know, what
is it that makes one generation connected to the past?
Why is it that generations resemble their forerunners? Um? What
what are these connections? And uh, genetics provided a huge

(28:21):
part of that answer, which is that well, genes get
copied and then transmitted through eggs and sperm and uh.
And so that was a huge revolution and understanding. But
that doesn't mean that that is all that heredity can be.
I mean there's still the at least the logical possibility

(28:43):
that there are other ways that each generation be can
be connected to the to the previous ones. And so
in my book I talk about different forms of heredity
that scientists are exploring. Um. And so you know, one
one very sighting possibility is what you referred to as
epigenetics and epigenetics is kind of a broad term, but

(29:07):
roughly speaking, what it refers to is the molecules inside
our cells that control our genes. That that allows some
genes to be switched on and to produce proteins and
others that are kept silent um. And you know, it's
it's very clear that this is incredibly important to our existence.

(29:27):
You know, it's what makes your skin cells be skin cells,
and you're you know, brain cells be brain cells, like
they are using different genes in the same genome. And
when these cells divide um, the you know, a skin
cell does not normally instantly become a neuron or or
you know it doesn't you don't grow a tooth on

(29:48):
your back of your hand um. And that has to
do with epigenetics um. And so what does this have
to do with heredity, Well, you know, when the cells divide,
there are basically inheriting the genes and the epigenetics of
their mother's cell. But you know that the possibility rises, well,
what if you pass those down to the next generation altogether,

(30:10):
you know, through eggs and sperm um. And there's some
evidence that that that can happen. And what makes us
especially exciting is that you know, through our lives, experiences
can change the epigenetic makeup of ourselves. You know, so
if you if you get sick, if you smoke, if

(30:31):
you experience stress, those all seemed to have an influence.
And so the open question is, well, how much can
those experiences we have in our lives then influence future generations.
I think that the jury is still very much out
when it comes to people, um, but in other species,
especially plants, there's lots of it, and that that really

(30:54):
is something that happens. You know, a plant goes through
a drought and generations later there's still an epigenetic mark
on its descendants. So yeah, epigenetics is in a really
exciting area. So you just alluded to some of the
controversy about epigenetics, and I guess there are other forms
of ideas of non genetic inheritance, but epigenetics in some

(31:14):
ways still remains controversial, especially in humans. Like you're talking about,
if you're comfortable speculating and if you had to guess,
how would you imagine our picture of non genetic inheritance
might change over the next fifty years or so? What's
your sense? You know? I think that it is actually
possible that we'll just find that, um, human epigenetics is

(31:36):
just not really that important. I mean, I'm actually I
think there's a reason to be kind of pessimistic. Um
that you know, there are these very cantalizing studies, but
they're small, and they could just be the result of
noise and so on, and and yet you know, we
really want epigenetics to be real. Um. I mean, epigenetics

(31:56):
has totally taken hold of the popular consciousness. And you know,
I was astonished to learn not long ago that you
can take classes and epigenetic yoga, which is not kidding,
you can google it. And the thinking is, the claim
is that you know that by doing this yoga you

(32:16):
change the epigenetic profile of yourselves. And you know I
and you know there are psych psychiatrists who will offer
you epigenetic analysis to basically undo the trauma that you
inherited from past generations. Um. It really speaks to us
in a very profound way. But I actually don't think
the science is going to really hold up very well. Um,

(32:39):
because are but I don't think it looks like our
biology just doesn't really allow that to make much of
a difference. But you know, the flip side is that
culture UM is actually, I I would argue, an incredibly
important form of forredity, especially for our species. We we
passed down not just our genes to the next generation,

(33:02):
but all of our knowledge and and beliefs and customs
and so on, and those those get propelled down through
the generations UM in a very hereditary way and UM,
and that's actually very different from other species. And I
would and you know in the book, I talk about

(33:23):
how you could argue that civilization itself is the product
of our very special form of cultural inheritance. So in
talking about non genetic inheritance, you've got potentially epigenetics, though
the juries out on that, you've got, you've got culture.
But we should talk a little bit about microbiology. Can
you tell the story of how you found out that

(33:44):
your belly button contained bacteria only known to exist in
the Mariana Trench? Absolutely? Yeah. So I've been incredibly fascinated
by the microbiome, you know, all the bacteria that live
on us and in us. For quite some time, him
In and I have been doing some reporting on it
as scientists have found new ways to to explore our microbiome.

(34:09):
And it used to be that you just have to
scrape you know some you know, a little bit of
skin or take a stool sample and taken into a
lab and try to grow bacteria. And the fact is
that very few of the bacteria that live on us
uh or in us enjoy being in a petri dish

(34:31):
on their own. It just it makes them miserable and
they don't grow. So we had a very impoverished view
of this inner world until scientists were able to just say, okay,
we're going to grow into this sample and just grab
out all the DNA and we're gonna sequence all the
DNA and from that we're going to figure out what

(34:52):
is in there. And that totally revolution I studied the
microbiome because now you didn't have to grow these critters.
You could just fish out there DNA and look at that.
So it turns out we have hundreds, maybe thousands of
species in our guts and on their skin and so
on and um and so you know, one day at
a meeting, UM I was walking past a scientist who

(35:14):
was holding out a qute tip and he said, I'm
doing a study on people's belly buttons. Would you mind
giving me some of your belly button lint. Belly button lint,
and I want to see what's in there, you know,
and for someone like me, you don't have to ask
me twice. I'm like, give me that cute tip. So
you know, I go off into the bathroom and I,
you know, fiddle around and dunt get in a little tube.

(35:36):
But they gave me and handed it back. And then
they went off and they looked at all the DNA
there was on that cute tip, and you know, a
lot of it was my own skin cells, but then
a whole lot of it was not um. And actually
they identified fifty three species as I recall, of bacteria
just in my belly button, and uh, it was amazing

(35:59):
to to look at, uh the information about each of
those species. And so one of them it had only
it's only known from a sample at the bottom of
the ocean. They marry on a trench um. And there's
another one that I have that's only been found in
soil in Japan. I've never been to Japan, so um.

(36:25):
But you know, this was entirely unsurprising to this scientist,
because you know, he was looking at lots of people
and was finding people with you know, over a hundred
species just in their belly button alone and from all
sorts of different places. UM. So what does this have
to do with heredity? Well, you know, I I did
not inherit that marry on a trench bacteria from my parents. UM.

(36:49):
It's just you know, we have all of this, these
these bacteria in the environment, um, and some of them
have become very well adapted to living on our body um,
and we just pick them up um through our life.
But it does seem that the microbiome that there is
some heredity to it. UM. The best examples come from

(37:13):
certain animals like that passed down bacteria to their offspring.
Then these bacteria can only live inside these animals, and
without those bacteria, these animals die. The cockroaches are actually
a great example of this. So you know, one reason
the cockroaches are so successful is because they harbor one
species of bacteria in a special little organ um where

(37:35):
it breaks down some of their food and gives them nutrients. Um.
And these bacteria never live outside of the cockroaches, and
actually they're they're sitting inside of cockroach cells and then
in the female cockroaches, those cells crawl over to an
egg and rip open, and then the bacteria infect the eggs,
so that cockroaches are born completely infected with these bacteria.

(38:00):
That's that to me, just seems that's heredity. I mean,
these bacteria are being passed down from millions of years
from parents to offspring. Um. So the question now is, well,
are is that true for humans? Um? Maybe not, uh,
you know, in that particular way, but um, you know,
it is possible that there are a lot of species

(38:20):
that are very much adapted to us. You know, maybe
mothers are passing down certain kinds of bacteria and the
birth canal or during breastfeeding. Um. And maybe the most
dramatic example of all is that in all of ourselves
we generate fuel with these little blobs called mitochondria, which
have their own DNA in them. And the reason they

(38:41):
have their own DNA is because they started out as
bacteria and about two billion years ago and our single
celled ancestors, those bacteria infected our ancestors and then took
up permanent residence in there and we cannot live without
them today. So um so, so MicroB is gonna have
a very powerful part in heredity. Do you think our

(39:05):
expanding consciousness about the full scope of heredity, from like
cross generation into symbionts or even to camerism, should force
us to re examine our ideas about what it means
to be an individual and individual animal and what the
biological and categorical boundaries of the self really are. Absolutely, uh,

(39:27):
you know, I think that uh, you know, heredity does
not actually follow a lot of the simple rules that
we assume it does, uh, and it and it does
bring into question what it means to be an individual
because you know, we think of he started out with

(39:50):
some original genome in a fertilized egg, so we inherited
half of that genome for me to our parents. It
came together in this new combination and that's us. But
you know that is not actually us. Um and in
lots of different ways. So in one way, I mean,
if you actually follow the cells that divide in an embryo,

(40:14):
those cells can mutate and then you tate again and
youtate again, so that if you were to look at, say,
any two neurons in your brain, they would be different
from each other because they have acquired different mutations as
we developed. UM. So there is no one genome in
our body because we are what scientists say call us

(40:37):
our mosaics. UM. But then that's not the not the
end of it. Um. So you know, we think of
heredity is going down through the generations, but heredity can
also come back up in reverse. Uh. And so one
example of this is um when when and become pregnant, uh,

(41:02):
cells from their fetus will circulate around in their blood.
You can actually you can actually draw blood from a
pregnant woman and sequence the genome of the fetus. Uh.
We that is done in a regular basis. Now uh
after pregnancy, Uh, those fetal cells may go away because

(41:24):
of the mother's immune system is clearing them out. But
surprisingly often UH those cells can establish them cells in
a mother's liver or thyroid gland, even her brain. And
scientists refer to uh such people as chimeras. Um. It's
after the you know, the beast of Greek mythology. And

(41:47):
you can get chimeras also from twins in the womb
who are sharing DNA sharing cells uh. And so you
can literally like have um. You know that one of
the first discoveries of this was a woman who gave
blood in the nineteen fifties and totally baffled the blood

(42:10):
bank because she was giving two types of blood at
the same time. And he said, this is not possible.
You know, there must be some contamination somewhere. But it
turned out that her blood was made up from two individuals,
herself and a twin who had died when he was
in infancy. Uh. And so you know, and this is

(42:30):
not something that's rare. Timerism is probably quite common among humans,
and it really challenges these these ideas that we we
tell ourselves about heredity and individuality. One of the weirdest
and most interesting types of heredity you discussed in the
book is that I think you said it's eight or
so lines of contagious cancer found in nature so far.

(42:52):
Can you talk a little bit about contagious cancer and
does it make sense to think of this cancer as
an independent animal or organism of its own type, or
as sort of an infection from an original animals genome. Yeah,
this is where credity gets really weird, because you know,
when when cancer arises in our bodies, it's a it's

(43:18):
another one of these cases of mosaicism. In other words, Uh,
these cancer cells are gaining mutations that the rest of
the body doesn't have, and those mutations allow them to
reproduce quickly and to be very aggressive and destructive. Now,
UM cancer usually UH, you know, either is wiped out

(43:42):
by the body or is lethal. In either case, you
don't have cancer surviving beyond the life of its host.
We we think of that as being weird, but it
turns out that in fact cancer can endure UM. And
this was really first discovered UM in in a uh

(44:07):
in a case with dogs where dogs would be uh
developing UM these these tumors UH, and it was very
odd that they the cancer seemed to spread like an
infectious disease, and so people scratching their head over this,
and then they realized that actually what had happened was
that the cancer cells themselves were spreading from one dog

(44:32):
to another to another UM and so that the cancer
cells were not in fact related to the dogs that
they were in. And if you look at the DNA
of this cancer, it goes back to some dog that
lived maybe ten thousand years ago, and it has just
been spreading from dog to dog ever since, and it's

(44:52):
been mutating along the way. And it's and so it's
the thing that you know, it's it's what you call it.
I mean I don't know what we could call it,
but you know, some have argued that it should be
just given its own species name, because it's it's this,
it's this lineage of animal cells that has its own
genome UM, and has its own way of getting around

(45:14):
in the world. It's it's doing just flying UM. So
surely it deserves a name. UM. And then it turns
out that in a few other cases, scientists have founded
another species, so Tasmanian devils in Tasmania, they get a
facial tumor because they bite each other when they're fighting,
and they spread this cancer to each other. UM. And

(45:36):
this this cancer has actually arisen a couple of times
in Tasmania just in recent decades, so it isn't something
that only happened once a long time ago. And what's
most mind blowing is that some scientists stumbles across this
yet again, just in the past few years, UH in clams,
in shellfish UH and have discovered that there there's contagious

(45:59):
cancer in the ocean. UM. So you're swimming. As you're
swimming in the ocean, you're swimming around cancer cells that
are moving from host to host. An infectious cancer as
its own type of organism. What kingdom of life would
that be? Would it be an animal? I yes, it
would be an animal simply because it's descended from animals. Yeah,

(46:19):
I mean I would say they would have to be given,
you know, a place in the animal kingdom. But and
you know, maybe you should just still call it like
a species of you know, maybe the dog cancer should
be a species of dog. Maybe you know, canus canus
cancer or something. I don't know, I don't know, um,
but you know it's and you know, when when and

(46:42):
when you talk about or what makes up an animal,
you know, like, uh, what makes up up us? You know,
like we think of cancer cells as being part of ourselves.
They they originate from our own cells. But um, imagine
if your body was actually made up of your own
cells and then cells that came from someone ten years ago,
that that would be weird. Yeah. Alright, time for a

(47:06):
quick break. Then we will be right back for more
of our conversation with Carl zimmer Than. All right, we're
back now. We can't talk about the future of heredity
without touching on crisper. How is this technology affecting the
future of human redity? Well, you know, we're going to
have to wait and see exactly what happens, but certainly

(47:30):
the potential is profound. UM Crisper is just a few
years old, and it's this is this technology essentially to
zero in on any particular bit of DNA, cut it out,
and if you want, insert a different little stretch of
DNA in there. So um, this raises the possibility of

(47:52):
being able to cure hereditary diseases by rewriting uh, the
DNA in cells, you know, to repair or a faulty gene.
But what some scientists have been already exploring is, well,
what if you take human embryonic cells. What if you
take you know, human embryos are just a tiny little
cluster just you know, seven or eight cells, and you

(48:16):
use Crisper to rewrite their DNA. UM, let's say you
fix a hereditary disease in just this handful of just
as few cells. Well that if if you if that
if a person were to develop from those cells, they
they would have Crisper altered genes throughout their whole body,
and if they were to have children, they would pass

(48:38):
on those Crisper altered genes as well. And so you
know that that that these experiments have already begun on
on these tiny little human embryos, and so really, you
know what what needs to happen now is for us
to have a really a kind of global conversation about

(49:04):
whether we want to use this or not, whether it's safe,
whether it's ethical, UM, how do we feel about who
should have access to this? UM? Do we have the
right to alter future generations? Um? And you know we
and maybe we'll feel comfortable with, say, you know, eradicating

(49:26):
hunting news disease. But what if somebody says, well, yeah,
but I want I'm using IVF and I want to
just give my kids, Uh, this mutation that we know
reduces your odds of getting Alzheimer's? Could I do that
as well? And then you know what if you add
on other things? What if you add on things that
are not don't have to do with immediately treating some

(49:47):
pready disorder, but you know, change a trait, change, hair color, change, height, change,
all these things are people who are going to be
comfortable with that, UM and this all you know this
science fiction writers have had a monopoly on this conversation
until now, but I think that everybody else needs to
be talking about it too now as far as crisper

(50:09):
altered genes go, given like a near future scenario, would
they be detectable? What would somebody be able to say
to to look at individual's genome and say, oh, well
you've had there's gene altering evidence here. Or would a
future civilization be able to look back at our genetic
information and say, oh, well look here in this particular

(50:30):
family line, we see evidence of of of of crisper alteration.
That's an interesting question. Um, I I think you would.
I think that it would be possible if the people
doing the crisper changing um left behind, you know, a
mark of what they were doing, you know, a little

(50:51):
water mark. Think of it that way. You know, some
distinctive sequence of non coding DNA nearby that basically says hello,
you know this is this, this crisper alteration has brought
to you courtesy of such and such hospital. You know, UM,
you could totally encode a message in DNA people. You know,

(51:11):
people have enquoded entire books in DNA now, so you
could do that. Um, But if you if somebody decided
not to leave a water mark, then no, actually, I
think it might be very difficult to um to say, oh, well,
this person descends from a crispered ancestor knowing knowing tech companies.

(51:33):
I know we'd end up with like thirty page el
agreements in there, sure absolutely, But you know the problem
is that you know that over the generations that would
get that agreement would mutate and uh, you know, the
legal language would would change into things that the lawyers
didn't have in mind. So given the great power that

(51:53):
crisper has to to allow us to alter our chenes,
what what do you think are the best is you've
heard about how to guide it in a way that's
that's fair, that's uh going to have good outcomes and
not bad that uh you know the people have access
to in in equitable ways. I mean, have you encountered

(52:16):
anybody who has done the best what you would consider
the best thinking so far on the ethics of gene alteration?
You know, I I in the United States, the government
is really just being very uh emphatic and not wanting
to really talk about these issues at all. So uh,
you know, not only is it not allowed to do

(52:39):
germ line modification, but you can't do any research that
might lead to that, and so um, we're not really
having a meaningful conversation in the United States. Yet I
think UM and UH. Unfortunately, what that means is that
people are going to want to go to other countries

(53:00):
where there is no particular regulation one or the other
and do that in you know, in UM, in you know,
clinics or that are hidden from view. UM. And in
my book I talk about one case where actually this
has already happened. UM. A couple went to Mexico and
an American doctor joined them there to uh to basically

(53:25):
replace the mitochondria in this woman's eggs with with healthy,
healthy ones. UM. So you know, there are some genetically
modified people alive today. UM. There there are a few, UM,
but they're they're already here. UM. But they I think
that it's a better, better way to deal with this

(53:48):
is what England is doing. So in England this treatment
called mitochondrial replacement therapy. UM. There was there was a
lot of research that was done on it, um uh
using animals, using using you know, eggs, human eggs, and
so on and then UM and then Parliament actually had

(54:09):
a big, full debate about it and you know, the
advantages and the possible risks and the ethics and so on,
and then they decided, well, we're going to allow this
to happen, but it's going to happen under these rules.
So you know, you can't just like walk into any
doctor's office and get this therapy like that. You know,
we're gonna really make really uh take We're gonna take

(54:33):
real care to make sure that this has done safely
and responsibly and under the right circumstances. And so now
there is a university that has actually you know, gotten
permission to basically open their doors for business UM. And
I think that's the way to go UM, because then
you can you can have these discussions and say, like,

(54:53):
you know what, as a society, we don't want uh
people to be trying to make their kids more intelligent
by altering their genes. We think that's a that's bad
for individuals and bad for society. We're not going to
allow it. Um, and that will actually happen rather than
sending people to other countries to have you know, possibly

(55:14):
dangerous treatments. UM. That's the way I think uh things
should go. UM. And you can see an example of
it in England. And it would be great if if
the United States could follow suit, you know, on this
show a lot we talk about how often like science
fiction is sort of the playground for people working out
these problems before they're dealt with in the real world.

(55:36):
Have you encountered any any science fiction or fiction in
general that you thought did a good job of dealing
with you know, raised the interesting questions, had intelligent things
to say about the implications of genetic engineering and humans.
Oh yeah, I think that there's a long tradition of

(55:56):
genetic engineering in science fiction. Um and uh and even
before people really knew what genetic engineering was. You know,
A Brave New World is a fascinating book even now.
I mean, and it's amazing when you think how um,
how much uh uh was just only discovered after the

(56:19):
publication of the book. Um and I I find that
one quite quite prophetic. I think the problem with science
fiction comes when people think that anything can happen. That
when people think that biology allows anything you can imagine
to be a possibility. Um and the fact is that

(56:44):
biology doesn't work that way. And so you know, when
when we're actually talking, you know, today about well, what
are the real possibilities that Crisper could create? I think
we need to sort of I think we need to
make sure that we're not um, just letting our fantasies
run wild. You know. Some people have said, like, oh,

(57:06):
well you'll just be able to um Christoper your kid
and and turn them into a genius. UM. And that
it's not what science indicates. I mean, you know, intelligence
is this incredibly complex phenomenon that is, you know, influenced
by genes, it's influenced by the environment. It's partly a

(57:28):
social thing, you know, in terms of like you know,
intelligence really sort of gaining its meaning in you know,
in a society. UM. And you can't just zoom in
on a on a few genes and make a tweak
here and there and say ah ha, like now my
child is going to you know, get into the very
best colleges. It just does not work that way. UM.

(57:49):
And and I think that if people just go ahead
with it anyway, UM, those children are going to be born, um,
not just with these odd little changes to their genes,
but with a whole huge set of expectations um from
their parents. You know, I spent a hundred thousand dollars

(58:10):
to change your genes to make you a genius. And
why are you getting these grades in math? What's what's
wrong with you? I just see a That's where I
see the real dystopia emerging. Is just expecting heredity to
do much more than it can possibly do, uh to
to alter ourselves. That's really interesting and it raises another

(58:31):
question that definitely comes up in the book, which is
that even when we're talking about traits that are to
some large extent heritable, what are some of the reasons
that it can create misunderstandings for us to talk about
there being quote a gene for a certain trait. Yeah,
we really have come to look at genes as being

(58:51):
all powerful and and that is a real mistake and
it's but it's hard to really um get your head
around the paradox of heredity in this regard um. And
one of the examples I like to talk about is height.
You know, height seems like it's simple, like it's just

(59:12):
it's just a number that you get off a tape measure,
Like how hard could that be to understand? But you know,
in in fact, um, you know, heredity is this very
weird mix of genes in the environment. Um, you know
gene so height is is very what scientist say, very heritable,
meaning that if you look at the variation among people

(59:37):
in a particular population. Why are they tall, why are
they're short? Uh, you can explain a lot of that
because of the genes that they inherited from their parents.
So tall parents tend to have tall children, short parents
tend to have short children. And it's so that means
it's very heritable. UM. But that does not mean that,
you know, height is somehow um law sped in and

(01:00:00):
fixed that. It does not mean that you can actually,
you know, finally predict um the you know how tall
it could will be, just based on their genes. In fact,
we didn't even know about any of these genes until
the past decade or so. Uh. And now scientists are
discovering literally thousands of genes that influence height, each one

(01:00:21):
in a tiny little bit. You know, I got my
genome sequence and discovered you know that I had. It's
very interested to find that a one particular gene. It
was the first gene that was ever linked to height
in population. And uh, I'm I'm about an eighth of
an inch taller than it would be otherwise because of
the variant that I have, So you know, it's it's

(01:00:43):
almost invisible. UM. But you know, the genetic influence just
is the some of all of these different variants. UM.
And yet on top of all of that, UM, you know,
you can have, you know, all the tall genes you want,
but if you're not getting a good diet when you're
a kid, and if you're facing dysentery on a regular basis,

(01:01:04):
you're just not going to grow that tall because your
body is going to be basically channeling all those resources
to fighting disease and to you know, fight defend against starvation.
And you know, on top of that, even more amazing
to me is that in the whole world has actually
gotten several inches taller over the past century because life

(01:01:26):
overall is better. You know, there's more people have a
better nutrition, better medicine. Education probably plays a role in this. Uh.
And so it's not that people inherited you know, quote
unquote tall genes, it's that they inherited a world that
favors greater height. So I've got one last question that

(01:01:47):
might be kind of weird, but we'll see what you
think of it. I often hear hear people talking about
their relationship with their own genome, um with their own
genes into basic ways. One is self identification, you know,
it's like, my genes are why I am like X,
and so there there's a sort of I identify with

(01:02:09):
my genes mentality. And then there's a kind of antagonistic
kind of thing people think about with their genes, like
the genes are this other disembodied force that made them
and it's almost like another person that they have to
negotiate with in some way. To what extent do you,
given all of the research you've done and after having

(01:02:30):
written this book, to what extent do you feel you
are your genes or that your genes are this separate
other force from you as a person. That's interesting. I yeah,
I've heard that kind of language too, you know. And
people will get their DNA sequenced and they'll discover they
have a particular variant linked to some train and say, ah,

(01:02:51):
well that's why I do X, Y Z, or or
they'll discover they have ancestry from a particular place and say, ah,
well that's why I that's why I like to tell stories,
or that's why I like to run or what have you.
Um And you know, you see ads on TV for
these companies like ancestry dot com that play on that
exact attitude towards our genes that somehow, you know, what

(01:03:15):
we do in our lives is encapsulated in these genes
that we inherit from our ancestors. Um. And then yeah,
then there are people who just want to fight against it, um,
you know, and part of that sometimes feels like, you know,
it's it's sort of a displaced fight they're having with
their parents, you know, like I'm not gonna be like
you were, you know, and I don't care if I
inherited gens from you. I'm going to be my own person, um,

(01:03:38):
I would say, in my own experience. UM. You know,
I got my genome sequenced and part of the research
for this book, and I really looked at it very deeply.
It's been a fascinating experience. But I can't find anything
in there that is quote unquote me. I think that
it's just not there, you know. I I was able

(01:04:01):
to look at the genes that I inherited from Neandertal,
you know, tens of thousands of years ago, and you know,
which is fascinating. But then I say to these scientists, like, Okay,
you've given me this catalog, got the indertal genes, let's
talk about them. Like, what what does it mean that
I inherit this particular Like, here's one gene, Tell me
about it, and the scientists be like, well, it looks
like no one actually knows what this gene does at all,

(01:04:24):
you know, and then that you're just left there. But
with the state of the science, you know, maybe I
found that I have a neandertal gene that UM is
linked to an increased risk of nose bleeds. I don't know.
I don't know what to do with that, you know,
And it also makes me wonder why neandertals might have nosebleeds.
But that's a whole separate issue. But you know, I

(01:04:47):
I don't I I can't say that anything I've done
looking at my own d d n A has given
me some deep insight about my inner self as a person,
you know, as it's much more relevant to me to
think about, you know, how my parents raised me and
what my experiences were as a kid, and what it

(01:05:09):
has been like, you know, being married and and and
being a father, Like the lived experience matters much more
to me than UM than the details of the genome
I inherited from my parents. UM. And that's that's kind
of where it stands for me now, all right, yeah, well, well,
thank you so much, Carl. It's been a real pleasure

(01:05:31):
talking to you today, and we appreciate you taking time
to speak with us. My pleasure, my pleasure. I really
enjoyed the conversation and I'm I'm glad you enjoyed the book.
So there you have it. Thanks once again to Carl
Zimmer for coming on the show and having this wonderful
chat with us about his new book, She Has Her
Mother's Laugh, The Powers, Perversions and Potential of Heredity Again.

(01:05:54):
That's available in hardback, as a digital and as an
audiobook right now, and you can check out Carl's website
Carl Zimmer dot com for even more about him and
his projects. That's right, go to that website. And hey,
be sure to check out our website as well. It's
Stuff to Blow your Mind dot com. That's who you'll
find all of our episodes. You'll also find links out

(01:06:14):
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(01:06:35):
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(01:06:57):
Is it how stuff works dot com. They four stars
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