An Evolutionary Journey through Domestication

An Evolutionary Journey through Domestication


Professor Schaal is the Mary
Dell Chilton Distinguished Professor of Biology at
Washington University in St. Louis. She is also the
Dean of the Faculty of Arts and Sciences at
Washington University in St. Louis. She is nationally
and internationally recognized for her scholarship
over the last many years. And she was one of
the first people who was looking at evolution and
populations and domestication history to really get in
on that wave of using DNA and the molecular world to
infer some of the insights that we might now think
are quite remarkable, and were unimaginable
just 20 or 25 years ago. She has over 200 publications. She’s trained 36 PhD students. And she has advanced our
knowledge in everything from systematics, to the
biology of invasive species. She’s worked on the
way that genes move between populations in nature. And she’s done some
amazing things, although we won’t hear
about rice tonight, she’s been very important in
understanding and uncovering how the domestication
history of rice, one of the most
important food crops in which humans have essentially
grown up over the last 10,000 years. She’s done some
extraordinary work there. But she’s worked
on pitcher plants. If you like blackberries
and raspberries, I guarantee you she’s had her
hand in some of those things. Right? Yeah. It makes me hungry just thinking
about all of this stuff. And she’s also done
some things that are outside of the laboratory
and outside of leadership within the university context. She’s been the President of the
Botanical Society of America. She’s been the
President of the Society for the Study of Evolution. And she’s been President
of the American Association for the Advancement of Science. She’s an elected member
of the American Academy of Arts and Sciences, and
the US National Academy of Sciences, where she served as
Vice President for eight years. Former Secretary of
State, Hillary Clinton appointed her as a
US Science Envoy. And from 2009 to
2017, she was a member of President Obama’s
Council of Advisors for Science and Technology. I don’t think there are
any advisors for science and technology right now. So she might be out of
a job on that front. I say no more. It’s a great pleasure to welcome
Barbara here to this lecture series, and to Harvard. She has been an inspiration
for so many of us through just a total
devotion to plants from her growing up days. And I’ll just add, at the
National Academy of Sciences website, if you’d like to hear
something quite wonderful, there’s a wonderful interview
that they did with you that’s posted there that
goes back to your childhood, and reflects on what it means
to come to a career in science and botany and a love of
plants that I would encourage all of you to stream. Anyway, Barbara welcome. Well thank you. That was really very, very nice. It doesn’t sound
like anybody I know. I’m really absolutely
so delighted to be here, particularly on a
series that deals with evolution because evolution
is such an amazing process. And it’s so just
wonderful and interesting. And so I’m really
grateful to the Doctor Sewitt for providing support
to have a series on evolution. And I know I’ve talked
to some other folks that have given lectures
in the series and they’ve talked about
how enjoyable it was and how much fun it was
interacting with the audience. So thank you all for being here. So what I’m going
to talk about is something that is
really interesting, and that is the relationship
between biological species and humans. This has been going on for
a very long time obviously. And domestication of
plants and animals started maybe 15,000
to 13,000 years ago. And it’s actually
continuing now. And so we’re going to look
at the course of that, and some of the differences
between plants and animals. But let’s begin with just
looking at human populations. So plants and humans
have a co-evolutionary– plants and animals have a
co-evolutionary interaction with each other. And when we talk
about co-evolution it means that one
species as it changes influences the other species. It responds in response
to that change. And it goes back and forth. And this is really what
has happened between humans and a lot of biological species. Of course, the very first
thing is food, the relationship of food to humans. And this is one of our
ancestors, Australopithecus. And one of the
interesting things is that of course this hominid
was adapted to the food that it ate. And the thought is that looking
at the dentition, at the skull, it probably was a forced
organism that ate large nuts. You can see little nuts
in the corner there, tubers and things like that. And so it required a powerful
jaw, thickened enamel, there we go, on the teeth. And as humans evolved, if
we look at a human skull, this one didn’t have
a copyright so that’s why it’s got a screw
in its head, you can you can buy this at
universalmedical.com. And you can see the skull
here, the teeth are smaller, you don’t have a
brow ridge, and it’s thought that as humans began to
eat animal food, and to cook, that it was more digestible. So the skull was modified. The gut, it’s estimated
it was very long when you have very coarse food. And our gut, the estimations
are that it became shorter. So there was an
adaptation to food. This is over the
course of evolution. We can look a little more
recently about such things as when we had domestication. So this is a picture
of plowing in Taiwan. It’s going to be a rice field,
so no plants but it’s close. And as humans began to
domesticate cattle, and camels, and goats, and
horses, they first incorporated them into
their environment, and then began to drink milk. I think, as many of you
know particularly if you’re lactose intolerant,
that we have lactase and we can consume milk when
we’re very young mammals, when they’re very young. And as one ages you no
longer have in the course of evolution milk in the diet. And so we lose the ability
and become lactose intolerant. If you look at where there
was an original domestication of cattle, Neolithic farmers,
which are in these dark areas here, and then lay on
top of that in Europe where there is high frequencies
of lactose tolerance throughout the lifecycle,
there’s a correspondence. Even if you begin to look at
diversity of milk alleles, there’s a correspondence. And so even in the
evolutionary differences in the polymorphisms
within this group here, it’s the result of the
kind of food that we ate. And again, this happens all over
for different kinds of milk. So independently there
has been lactose tolerance for camel milk and for goat
milk, and different genes– different origins of this. So many people
feel that while we have the internet and Facebook
and we have airplanes and all of the amazing things
that happen now, strontium lattice
clocks, and GPS, that domestication
of plants and animals is probably the most
significant development over the last 10,000 years. Because what it allowed, was for
a much more consistent and more abundant food source. And so that’s what
allowed the opportunity to develop permanent villages. It allowed the human
population to grow. I’m not sure if you’d want
to call it an explosion. And it allowed a
division of labor. And it allowed
individuals to develop various kinds of technologies,
such as brewing beer, and which is an important one,
and also to develop culture. And so this is one of the
very earliest cities where again, there’s archaeological
evidence of plants being domesticated
and plants being used. So we’ve seen how the
association with plants and animals has changed humans. So humans have responded
to their diets. What we’re going
to talk about now is how plants and animals have
responded to their association with humans. And so the general feeling is
that animals, a major change and there’s many of
them, but one of them is that animals became more
docile and less fearful. It is natural for wild
animals to become aggressive when confronted. We see that very often. If you’ve ever seen a
skunk that gets angry, it’s pretty aggressive. And also, it’s very
common for them to be very fearful,
particularly hoofed animals. When they become frightened
they’re very, very skittish if you will. When they became
domesticated they’re much less aggressive,
much less fearful. Plants, when they
were domesticated, became easier to grow. Lots of changes in terms of
the ease of germinating seeds. They became also more robust
and they had a greater yield. And so these are
some major changes and we’re going to explore those
changes in plants and animals. And of course, some of
the Egyptian artwork really shows the
relationships between animals and plants and humans. So domestication is an
evolutionary process. When we say that a
species is domesticated, it means it has
undergone genetic changes from its wild ancestors. And I’m sure if you’ve been to
other lectures in this series, you know that there’s
sort of this name almost about domestication. And this is what
Charles Darwin showed, was that species are
genetically variable. So that if you go
out into nature and you look at a species
there’s variable traits. It could be traits
for robustness. It could be variation
in flower color. It could be all sorts
of different things. And this genetic,
then this variability has a genetic basis. And so that’s sort of the
substrate for evolution, genetically variable traits. And then for domestication,
some of these traits are going to be more favorable
in human environments. They’re going to with
animals cause the animal to be less fearful. For plants, they might the
ones that have better seeds or are better tasting. So there’s going to be
among the wild variation, the natural variation in the
species, some of the variance will be more
appropriate for humans. And then what
humans will do, they will select individuals
with these favorable characteristics. And this can be
done consciously, or it could be done
without even thinking about it, without particularly
selecting for something, but just simply by association. And so those individuals
that are most adapted or are most related to
humans, or that are more comfortable
around humans are the ones that will then
be used for producing the next generation, the
ones that will be bred or the seeds that will be
gathered and then planted. And so that is the
evolutionary aspect of this. And this has been
an amazing process for the history of humans. It’s amazing for
archeology to look at. But one of the
interesting things as an evolutionary biologist. Is that this has been very,
very strong selection. Very strong selection on
the genome of organisms. So when we start to look at
the consequences of selection in a theoretical way and
in an experimental way, we very often use
natural plant species, that’s what I work with, to
look at selection because it is so strong and so powerful. And we know a lot about the
basis of selection, which I’ll show you in a little bit. So this is not only
an amazing process that has important consequences
for humans and for the course of our culture and
civilization, but it also provides some very
important model systems for studying evolution. Just one little aspect
of the evolution in domesticated
species, and that is the concept of a
genetic bottleneck. And so if you go out and
there’s a wild species, we talked about
Columbines before– this, not–
Columbines the plants. And they’re variable. If you wanted to select one
type of them, what would happen is that you would choose
just a few individuals. So if this were a wild
population of wild horses, of wolves, of Columbines, of
the ancestor of rice, what would happen is
humans would basically pick only a few individuals
for the next generation. Those would be the individuals
that were the most docile. Those would be the
individual rice grains that were the largest
or the most fragrant. And that would found
the next generation. So what this does is it
reduces the genetic variation. And it also very often
changes the morphology just simply by sampling. So this constriction
of population size is something that people
use to study all the time. So what happens during the
course of domestication? Well, because of the
genetic bottleneck, there’s a reduction
in genetic variation. There are morphological changes. You’ll see some of them are
directly selected by humans, and others happen
as a consequence, an unintended
consequence of selection. For animals, there’s
behavioral changes. There’s also changes in
the timing of reproduction. And then something that we’re
not going to talk about, but that is very,
very interesting, and that is very often in
the course of domestication it’s not an abrupt isolation
between the wild ancestor. Wolves gave rise to dogs. It’s not an abrupt isolation. But rather there’s
crossing back and forth. And particularly
in populations that are very closely associated with
humans such as rice or cattle, humans when they migrate, and
of course the human history is migrating from one place to
another, lots of migrating populations, they took with
them their domesticated animals, and they’re domesticated
plant seeds of rice, and all sorts of things. And then there would be
hybridization and crossing with not only any
wild ancestors, but also with perhaps
sometimes other species. We see that in the
domestication of cattle. So some very, very
complicated evolutionary histories, and very, very
difficult to unravel. And some of the more
recent work is really looking at these
processes and trying to figure out how actually
did domestication occur. So one of the interesting
things that Charles Darwin noted throughout his work
on evolution is that there was
this domestication syndrome in animals, a
suite of characteristics that come together. And what he noticed was
that domesticated animals tended to be docile. We understand how that happened. Those would be the individuals
that you would want around you. But they also
develop floppy ears. And nobody’s selected
for floppy ears. In border collies, it’s
exactly the opposite. You want pointed ears. Also, all of a sudden he noticed
that the wild ancestors might be uniform in color,
but the domesticates had all kinds of
variation in coat color. And did humans select for that? He didn’t think so. It seemed to be– it was sort of
a mystery to him, a conundrum. Reproduction, timing of
reproduction changed. Skull shape has changed,
and there’s also a lot of size variation. So this has been a puzzle. How did all of this happen? And the thing
that’s remarkable is that we see it– get ready for
a lot of cute animal pictures. This is completely, you
know just gratuitous animal pictures. But what it does show is
what Charles Darwin noticed, is here you got all
these floppy ears. Here’s a pointed ear one. But a little piglet with
floppy ears and that’s sheep. And that’s a floppy
eared animal, a rabbit. And the other thing
that you notice is that there’s
variation in color. And I think the rabbit
and the little piglets are a good example of that. It’s very common to see
domesticated animals be spotty. So how does this all occur? Darwin thought and
folks have thought that this was the result
of sort of the consequences of selection, but unintended
consequences of selection. So we’ll get back to
that in just a moment. There’s been a lot of work done. This is from Zeder in
2012 about domestication, particularly of animals. And so it’s thought now
that there were actually three different ways that
domestication occurred. One was a group of organisms
that were commensal, there was a commensal pathway. And that meant simply that
there was wild animals that tended to associate with
human habitations, things like dogs and cats, because
humans of course have waste. They have garbage
piles, waste piles. Seeds will germinate there. A human habitation attract
small mammals and predators are attracted to that. And so there was this
suite of organisms around human habitations. One of the early hypotheses
was that humans domesticated animals because people
kept the young little baby animals as pets. And that now I think is less
prominent and there’s much more thought that it was
this commensal pathway. But there was another pathway
where the organisms, so dogs and cats would be an example
of this, another where the organisms were first prey. And that would be things such
as horses, and goats, and sheep. That first humans
hunted them, and then in the course of interacting
with these species they slowly began
to manage the herds. They would for example
only kill males and let females live because
they would reproduce. And so there was
this prey pathway. And we’ll talk more about that. And then finally, just
the directed pathway. In many cases with
many organisms that are long term
domesticates, after a while it’s not inadvertent
selection for something. It’s very, very directed. So modern plant breeding, the
breeding of dogs and horses, all of this is now very
conscious selection, artificial selection. And this is interesting because
we are domesticating, even as we speak, some new species. So the commensal
pathway, it is not intentional because
the human niche, our camp sites
attracted animals. This is very early picture
of a dog with a hunter. And what happens is that again,
the most docile, least afraid gets food because it’s
close to human habitation. And so you have just
by the animals that are non fearful being able
to go and grab some food that has been cast off or grab a
bone that’s been cast aside, this is this kind of
inadvertent selection. And the course of
this is habituation. First the animal gets used
to being around humans. Then it in fact
becomes not dependent, but uses a commensal
relationship. And then you develop
a partnership, a hunting partnership. And then there’s
actually domestication, the genetic changes
association with domestication. And then later on in the course
of a much more recent times, then actual genetic
domestication where you select for
particular characteristics. So let’s look at the
domestication of dogs. It’s thought that dog
domestication was the earliest domestication. And dogs come from wolves. Canis lupus. And there are two species, not
two species, two subspecies, the European Grey
Wolf, which gave rise to one lineage of
domesticated dogs. And then the Asian
wolf which gave rise to another lineage
of domesticated dogs. And domesticated dogs have a
fairly complicated history. And one of the remarkable things
about looking at domestication studies is the advent
of using genomics to understand the relationship
among wild ancestors and the domesticated
species, and looking at the course of domestication. One of the thrilling things
that’s happened in the last 15 years is the ability to take
bones from archaeological sites to get DNA, and to
analyze that DNA and then compare
it to individuals from different sites,
and also extant species and wild species. And so we’ve really made
a tremendous progress by this sort of
genomic archeology. It’s very, very exciting. And I think there’s some
really wonderful work that’s done here at Harvard looking
at human evolution, which is just I think that the
results are mind boggling. And species that we didn’t
know about that are ancestors, it’s very exciting. And likewise with
animal domestication. So there’s been a
number of studies that have tried to understand
the domestication of dogs from these two subspecies
of canis lupus. And so this is what’s
thought has happened. You have in the ancestral
wolves way back in time. You have Asian wolves. Ancient Asian dogs
to modern Asian dogs. And then again,
humans move around and good things
get passed around. These Asian dogs
were transported over at the same time European
wolves were being domesticated paleolithic European dogs. We have DNA from some
of the Neolithic dogs and here’s the
Newgrange dog which we have DNA from 4,800 years ago. Modern dogs and again, this
movement back and forth. And of course now with
modern animal breeding and with people really fancying
various breeds of dogs, there’s just a huge amount
of crossing back and forth. So this is the history of dogs. And we know this because
of studies of ancient DNA. So the yellow parts are
the modern European breeds. The red are the Asian breeds. Down here, you’ve probably
all seen these relationships. They’re phylogenetic
trees but it basically shows a groups things based by
their genomics, by their DNA. And so what we
see, the Asian dogs like [INAUDIBLE],, these a lot
of village dogs from Asia, they come out all here. Then we start to have
some intermediate. And then here are the
modern European breeds. And then right next to it
is this Newgrange Ireland, which is a dog from 4,800. So we know that that
dog at that point was very closely
related to the ancestors of the modern European breeds. The other thing that’s
very interesting, here are wolves down here. So there they’re
still quite different. This thing down here
that you can’t see is actually a wolf dog hybrid. And so all of this sorts
out to the ancestry, and to the domesticated dogs,
and to even some hybrids. So very, very good information
on the relationship of ancestral dogs. And a lot of this is really
edified because of the ability to use ancient DNA. And this is just simply the
distribution of those variants. And so you can see that there’s
this cluster of Asian dogs. There’s also lots of
potential hybridization. And then lots and
lots of dogs that have either a European
ancestry or mixed ancestry. So you can begin to see how
these genomes, these two genomes from the Asian wolf
and the European wolf sort out. So the changes. One of the things that
we can do is begin to ask about molecular changes. And there is an insulin like
growth factor, which people think is a gene, is related to
some of the size differences. I think one of
the amazing things is you have these
giant Great Danes. This looks like maybe a pug. We’ve got things that are
a lot smaller than that. And so in the course
of domestication there is this huge variation for
size that people have selected. And a lot of these
related to functions. So dachshunds and a
number of the terriers, they were for getting vermin. And so they have a
size, and a short shape, and a morphology
that allows for that. These are the skull variations. So lots of differences
in the skull. This is a gray wolf here. Very elongated nose, which
is the natural state. This is looking at the side. And you can see the large teeth. And then ventral, so looking up. And this is a Great Dane. This is a Rottweiler. This is a Greyhound. And Yorkshire terrier here. And this is our pug down here. So this is the ancestral
state and these are the kinds of
modifications that humans have been able to do. And a lot of this was
directed breeding. The initial domestication, the
initial changes, was probably do just inadvertently, but now
we have very strong selection on all of these different
characteristics. Let’s get back to
Darwin’s question. And this is something that
is relatively recently and it’s a very
interesting hypothesis. So in 1959 in Russia, Dimitri
Belyaev and Lyudmila Trut, I hope I’ve said
those names correctly but I wanted to shout out
their names incorrectly or not, they were beginning to
look at the silver foxes. These were used for fur
in the fur industry. And in 1959 they began
a domestication study. What they did was they
just simply selected for the next generation,
the wild foxes that were the ones that were
most receptive to humans, the ones that might come closest
to a human, the one that might take a little bit of food. And they did that
generation after generation. And what they found
in 10 years, this is the first pup that
appeared with floppy ears. So the selection
was for tameness and for lack of aggression. And one of the things
they began to get was floppy ears after 10 years. Only in 10 years. This is a picture of
Lyudmila with the foxes. And you can see obviously
they like her very much. They’re very social. And this is pixilated, but
these are some of the results. So after a period
of time you ended up getting a fox that looks like
one of my border collies. It has the spotted
black and white. It has a shorter snout. And one of the other
characteristics is that they begin to
develop curly tails. So they were able to duplicate
the domestication the way we thought that
domestication occurred. And you ended up getting
these unanticipated changes, floppy ears, and black and
white, and curly tails. So that’s been a real
question, how does this occur? How can you select
for domestication and for behavioral
characteristics, and end up with a suite of
morphological characteristics that we see once in one
species after another. So there is a neural
crest hypothesis. And the neural crest is
something that happens early in embryonic development. And it’s something that
affects the development of many different
parts of an animal. And so one of the things
that we see it affects– and the thought is that the
neural crest in some cases is less active,
there’s fewer cells, or there’s less
cells moving around. And so what it does affect,
what the selection is, is to really affect the
brain, and to reduce the parts of the brain that
cause the fight or flight response. So it’s thought
that that was one of the things that has changed. And as part of that, if there’s
less active neural crest, that you’re going to
have fewer melanocytes. So you’ll have pigment changes. It affects cartilage, and
so the cartilage of the tail might be different,
likewise of the ear. And this is a hypothesis. A lot of folks thought it
really explained everything. I think people have
pulled back on this. And now it’s thought that
it probably works in dogs, but there’s still lots
of work to be done. But a very interesting
idea to try to explain this sort
of inexplicable suite of characteristics. One of the things that
happens in domestication, and I always found this as a
dog and cat lover a little bit offensive, but is that,
and a horse lover too, is that when we look at
our domesticated organisms such as a pig,
and mink, and cat, and dog, and ferret,
sheep, turkey, and turkey we expect not to
have a lot of brains, but if you look
at them, they have compared to their wild ancestor
a reduction in brain size. And this is what we see
in all of these animal domesticated species. Pig, 33% decline in brain. Mink, 20%. Ferret, 30%. Turkey, 30%. We’ve got horse for 14%. Mouse and rat less. That’s probably because
there’s a lot of hybridization going on. So this has been a really
interesting consequence of domestication. And it’s thought it has
to do with specific parts of the brain that affect the
behavioral characteristics. That’s the hypothesis. So size of dogs brains
relative to wolves has decreased by nearly 30%. It may have reduced
areas of the wolf brain that enabled tolerance
to human contact. And it’s acute in
the limbic system, which is integral to
fight or flight responses. And so these are some of the
work and some of the papers that have done that. I want to talk about
one last thing. There is a series. It was in the public press. How many of you heard
about the study that was published in the Proceedings
of the National Academy of Sciences on puppy dog eyes? Anybody hear about that one? So this is amazing. So these are puppy dog eyes. I told you. I know, they’re so cute. This This is a wolf. Wolf eyes. And what you can see, they
tend to be kind of slits and you don’t have
eyebrows and everything. And so it tends to be
much more of a wolf like, or it’s a wolf like
stare, an intense stare. If you look at
domesticated dogs, they have little eyebrows. And their eyes get bigger. They’re able to, those of
you that have dogs you know, if you’re eating dinner and
your dog comes up to you, I mean it’s, you know
like, oh I’m so hungry. I haven’t eaten
in, what, months. And it’s very effective. And so the thought is that
in fact humans selected inadvertently for changes
in the musculature and in the structure
around the eyes, because if you look
at an animal and they look sort of like a like sad
and they need food or something, you’re more likely to
give food to the animals. And that was
inadvertent selection. So they examine this in
Kaminski, et al in this paper, in fact looked at this. And so this is the wolf,
and some of the musculature around the eyes. And then it’s much more enhanced
in the domesticated dogs so that you can actually
open the eye up a little bit. And so it’s a very
interesting case of potential
inadvertent selection. But I think all of us know
it’s extremely effective. Very hard to deny that. So let’s look at
the prey pathway. So that’s the commensal
pathway and dogs are really well studied. So this begins with humans
hunting, hunting for food. Goats, pigs, cows, and horses. And so what it’s
thought happened was that they began
to increase as there was more hunting pressure
on the animal populations. They began to worry about that. And so there was increased
pressure, hunting pressure on the prey populations. So there began early management,
taking only the males or taking males
preferentially to females, because the females would
contribute to reproduction. And then you began to have
actually herding, and having herds that were constrained
in particular areas. It’s thought that herding
may have occurred even before the development
of plant agriculture. And again, we begin
to see this associated with some human settlements. And then very quickly,
there developed after the herding became and
the animals became docile, then they developed other
uses such as transportation, the use of milk, et cetera. So one of the examples of
this is horse, is the horse. So horse hunting
was about 5500 BP. And it was domesticated
for actually hunting, for as a food source
but then the horses were used for actually
hunting, and for milking. And so some of the early
settlements where there’s archeological sites
tended to be like this, the reconstructions show the
beginning of horse corrals. This is one of the
famous Cave paintings of the horses that were
being hunted at that time. The timing is such that
these were being hunted. And then this is a picture
of a Przewalski’s horse. It was thought that
these few individuals, this is the remnant population,
were wild ancestors of horse. The most recent
thought is that these were very early domesticated
and then they escaped. And so this may not
be the ancestor. But if you go back there is
just a remarkable similarity in appearance. And so that’s another
pathway for animals. And then finally there’s
a directed pathway. And this is something that
happens much more recently. Again we’ve talked about this. This is just koi. And they are selected for
their appearance obviously. Now we have a number
of new domesticates. And so ferrets. Ferrets as pets is
a new domesticate. Something relatively
recent, ostriches. And then here are carp for food. And so in the process
of domestication there’s a number
of small animals that had been
recently domesticated. And then there’s also
a number of fish, aquatic species that are
being domesticated as new food sources. And so a lot of the salmon that
we eat is domesticated salmon. Now we want to talk about
domestication of plants. And so the domestication
of plants– this is an urban environment. It looks pretty bad picture
but compared to a field, it’s quite different. So what domestication
of plants allowed was for a much more reliable
food source, a food source that could be harvested and it
could be stored and used over a period of time. And again, this is
what people have thought led to the development
of permanent settlements, the development of
divisions of labor, increase in population
size, and culture. So this is a very important
aspect of what we do. And when you think about the
way that our civilization, the way that our countries
are being developed, that more and more people
are leaving rural areas and growing their own food,
but they’re going into cities. And so this kind of agriculture
that feeds these cities is something that is necessary
for this kind of urbanization. We could have a very
long conversation about the consequences of
this kind of agriculture. But I think there’s
a strong support that it would be very
hard if we didn’t have large fields like
this, we would not be able to feed these large
urban populations, which are millions. So what is the path to
plant domestication? So this path first is humans
began to forage for plants. They went out and they
gathered food, wild rice seeds in aquatic environments. They did that with canoes
and with other kinds of floating things,
rafts and things. Then the plants
became commensal. This is a picture of
a squash plant that is growing on a manure pile. It’s the best I could do about
what some commensal might be. So as people harvested
food, as they took food to their dwellings, their
tents, or their villages, and then they began
to throw out waste or if they gathered seeds for
harvest plants to harvest, they would cut the plants. And the seeds would be tied
onto the plants but some of them would fall off. So you began to have
a lot of the species that people were
foraging for were living around the environments
that people actually habitated. And so they became
much more conspicuous. Then it’s thought
the next phase is, and this is what we many
of us do in our gardens, when I see a volunteer tomato
I don’t rip it out as a weed. I usually just say, oh
good free tomato plant. And you just let it grow. That was probably another stage. And then finally, there
was the domestication, the conscious
collecting of seeds from the best individuals,
storing them for the next year, and repeating that
process year after year. So domestication in
plants was very directed after some of these
initial stages. So plants also have a
domestication syndrome. What happens in
plant domestication the first thing probably
is loss of seed dispersal. That means that the seeds
instead of flying to the winds, would be retained on the plant. And I’ll talk more about that. Another thing, of
course, very quickly, you increase the harvest. That’s the whole
reason for growing plants is to have a harvest. So harvest, the yield
per plant has increased. Also the plants
are easier to grow. One of the things that
we see is the wild plants can often be very large
and gangly with low yields. Our domesticated plants
are much shorter. They’re more robust. And they have larger yields. And then also tastier
and safer plants. This isn’t always talked about
but a lot of the ancestor to some of the plants that
we eat such as fava beans, have compounds that can
be quite unpleasant. In some cases they
can even be toxic. And so making plants tastier,
reducing these secondary plant compounds so that the
food is easier to digest and more tasty, more palatable,
is another course of selection that has happened in plants. Some of this very, very early,
and a lot of it much later. So some of the first crops. We’ve all heard about
the Fertile Crescent and of course that was where
we had domestication of wheat, and barley. Peas were an early domesticate. This is an African bottle gourd. This was domesticated
very early as a container. So not used for food
as much as a container. And then in the Americas we
had corn and also squash. Cucurbita pepo. Lots of different kinds
of cucurbita pepo. So these are some
of the first crops. Plant domestication
is interesting and a little bit different
than animal domestication. We have these areas, sights
of plant domestication. So in the United
States the eastern woodland Indians in this area
here domesticated a whole suite of different kinds of plants. A sunflower was it
was one of them. But many of those
plants we don’t eat now. We do use sunflower. But domestication
of corn, there’s a whole suite of plants that
were domesticated, again, independently in South America. Things such as Jack beans,
and peppers, and cassava. Domestication locations. The different colors
are for different times. In Africa, the Fertile
Crescent, and of course, in Asia we have rice and a number
of different crops, soybean, and India lentils, and
then also some things in Papua New Guinea. So plant domestication
is interesting because it happens so
many different times in so many different places. And this makes a lot of sense
because if something is good, to eat it’s going
to be domesticated. This is a really natural
kind of consequence of a relationship with humans. So one of the first things,
one of the interesting things about plant
domestication is because of the genomic revolution we
can now find out specifically what genes were involved
in domestication. So it’s a little
challenging in animals. But we seem to have gotten
a little further in plants. And so in plants, one
of the first genes that changes is a gene
for seeds shattering. So most native grasses and
a lot of our domesticates are grasses, when you pick
them and the seeds are ripe, they blow off and they
fall to the ground. And this is of course,
what makes a lot of sense for a wild species. If you would hold those
seeds onto a stalk well that’s kind of stupid. You’d have to wait not– not that the plants think,
but you’d have the stalk fall and you’d get all the plants
and little seeds germinating in one area. And that wouldn’t be
particularly good. So there’s been selection
to disperse seeds, and there’s many different
ways of doing that. If you’re a early
farmer and you’ve just cut a whole bunch of rice
stalks that you’re going to take and now you’re going to
thresh them, and on the way to where you’re going to
do this they all fall off and go to the ground, you’ve
just lost your harvest. And so very early genes that
affected seed shattering, and it’s called shattering
when the seeds blow off, very early on there is
selection for seeds shattering. And there’s a number of
different genetic loci involved. And this is rice. Actually there is
some rice here. There’s primary seed–
there’s primary genes and then genes that also affect it. And so you go from
this wild type where there’s no
seeds on the stalk. They’ve all fallen off. And to one where it’s held on. And here they’re
even bigger seeds and they’re held on
even more tightly. And we can begin
to analyze this. This is a wild type. This is African rice. Oryza Glaberrima. And this is what is an
abscission zone, where you’re going to see the results
of abscission zones in a couple of weeks. And that’s when the petiole
of a leaf, or the petiole of a stem, the stalk
develops a series of cells like this that then
allow this to break off, and the leaves to fall
or the seed to disperse. So this is the wild type. This is what happens in
nature in order for rice to drop its seeds so
that you can produce the next generation in nature. The non shattering
kind, you can see there’s a little
bit of those cells and this is a
transcription factor. It’s a yabby factor. You can see the cells here. But they don’t
connect all the way. And that allows the seeds
to be retained on the stock. And so really very
careful molecular analysis allows us to
understand these seeds. And when we have
modifiers the direction and the number of cells here,
this non shattering type is different. So you might have some that are
very close to being completely break off, and some that might
just not have very many at all. So one of the interesting things
for really understanding again this molecular aspect of
domestication, is corn. And the domestication
of corn is of course is an amazing, an amazing
aspect of plant domestication. So it really provides
a case study. So this is an old very
famous photograph. This is a very early kind
of domesticated corn. This is the wild ancestor
of corn, teosinte. Each one of these little
things here is a grain, is one of these kernels of corn. What you see, this
dark stuff here it’s a glume It’s this
like hard nut like case. And of course we’ve
gone from this to these more primitive
types of ears of corn, to the kind of corn that
we see in our fields. The other thing, so there’s
been lots and lots of changes. The wild ancestor, teosinte
here, it looks like a big weed. And if you were
looking at rice you would see the same
sort of thing. The wild ancestors
tend to be perennial, meaning grow year after year. They produce lots and lots
and lots of different stalks. And the yield tends
to be fairly low. And then the domesticated
maize that we have is very, very
different, because you can see that this is a whole plant. It has a single stalk,
not branched at all. Obviously a very
large ear of corn. So how do you get from these
multiple stems to this? Well there’s a gene for
apical dominance, tb1. So that’s been
analyzed and we know that that’s one of
the genes that’s involved in domestication. So in this case, when
humans were selecting for enhanced grain
production they were selecting on
specific genetic loci. And we see the footprint
of that selection when we do a genomic analysis of
the wild ancestor, teosinte, and the domesticated corn. Another one that I just talked
about is, this is teosinte and this is like a hard
shell around the grain. And this is a glume
architecture gene. So the glume– we
know glumes, like if you eat corn
sometimes you get parts stuck between your teeth. That’s the remnants of a glume. So this is a very hard glume. And then of course in
the course of selection you get something like this,
where the glumes are just those little bits and
pieces that stick. And the gene that’s
involved as tga1. So we know the genetic
analysis of that. And then finally, we
can do ancient DNA. And so the amazing thing about
the ancient DNA work is here, this is a corn cob
that was dated– in the DNA archaeological
work, what’s so remarkable is that
you have radiocarbon, you have dating of a particular
piece of corn or a seed. So you know about the date
of where that came from. And then you can do
genomic analysis. And so you have a date and
you can do the analysis and know what the genotype
was at that point. It’s really, really remarkable. So if you look at a modern– this is a pie
diagram of genes that are involved in domestication. So we’re looking at a
specific genetic locus. This is modern corn. This is New Mexico corn from
about 600 BP to about 1800. And then even older corn. And you can just begin
to see the differences in all of these
different kinds of corn. And so we’re able to really
get a very, very close idea of the actual genetic
course of domestication. So what does this all mean? Why do we even care about
studying domestication? Well many of us
care at universities because we just want to know. We want to know how did we
develop this association with plants and animals? How has that affected the
course of our civilizations? But there’s also a really
interesting aspect of this and that is the kind
of, if you will, the journey, the history
of domestication. So we started out with
probably individuals harvesting plants that were
growing out in the wild. I study rice and the native
populations of wild rice are sometimes very scarce. And I’ve always
wondered about how humans would pick this when
if you go now to Thailand and Cambodia and Myanmar, you’ll
find just little pockets of it, and you figure out why would
people ever harvest this stuff. And then I saw my
first population in an area that was
a marshy area where it was a native population
and it was a huge area. Water. And about the only thing you
saw were these wild rice plants. And so that’s the
kind of environment, that was the kind of thing that
humans gathered when they had these huge native populations. We don’t see them anymore,
particularly with rice, because if it’s a good area for
wild rice with lots of water, it’s a great area
for a rice paddy. So you don’t see that too often. But there’s this
kind of foraging. So non intentional
selection probably initially as commensals
all the way now to the future to
what we’re doing now, and that is gene editing of
our modern varieties of grains and many different
kinds of plants. And so this gets to a
really interesting aspect, because when we start talking
about genetic modification and gene editing, this
is kind of selection, but it’s selection
in a different way. But what we’re doing, is
we’re still transforming and we’re still changing. And the last thing I
want to leave you with is potential for
future domestication. We’ve seen this in animals. One of the most interesting
things about plants is that there are about
20,000 edible plant species. That’s the estimate. About 2,000 of them are
economically important. And about 30 of them provide
most of the world’s food. And so one of the things that
many people have thought about is there’s a potential for
additional plant domestication, providing new kinds of foods
from the wild species that are out there. And a number of plants have
been more recently domesticated. The kiwi berry is a good one. It used to be called,
was it gooseberry? What was– gooseberry. Yeah, that’s not
particularly exciting. And once you change
the name, then people began to really
domesticate it and to have a very large market. And this is just some of
the abundance of fruits that you see in the tropics. We don’t have quite
that level here, although with modern
transportation we’re beginning to see it. But such things as cassava,
and mangosteens, and rambutan, and all sorts of
different things make for really interesting
potential domesticated plant species. And so this course
of domestication, it’s of intellectual
interest, it’s academic, but it also is really practical. And it has allowed us to really
expand I think the kind of food that we eat. And particularly given the
sort of global situation where more and more populations
are becoming urban, where we have parts of
the Earth where, regions of the globe where
agriculture is really suffering because of climate change, this
whole idea of expanding what we use, expanding the nutrient
criminal quality of the food that we have, really
does rest on some of these basic
fundamental principles that first came out
in domestication. So with that, we’re very happy. We’re going to have some
microphones in the aisles and I’m really happy to
address some questions. So thank you for your attention.

1 Comment

  1. Matthew Zhang says:

    please post more, thank you so much for posting these amazing lectures.

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