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Before your parents were born,

and before your parents' parents were born,

and before their parents were born,

there were different kinds of plants

than there are now.

Before this, there was even a time

when there were no fields of

crops grown by farmers.

In fact, there were no farmers!

People gathered food that was growing wild

instead of growing it in fields.


In the days when farming was just beginning,

there were some kinds of wild mustard plants.


Our ancestors took seeds

from this wild mustard

and planted them in fields.


They took good care ...


The mustard seeds sprouted.

The roots grew into the soil.

The shoots grew into the air.

Some buds grew into leaves.


Green leaves grew larger.

The plants grew taller.

Some buds grew into flowers.



Flowers got pollinated.


Pollinated flowers grew into seed pods.


People noticed some differences

between the mustard plants.

Look closely.

Can you see any two plants that are the same?


In what ways are they similar?

In what ways are they different?


Why are they different?

Is it because some had more water?

Or less sun?

Or more fertile soil?

Or is it because the seeds

they grew from were different?



Once some people observed

that some mustard plants have seed pods

that are longer and contain

more mustard seeds than others.

They wondered why.


They used science to find out.



Why are some mustard seed pods

longer than others?



Maybe seeds from plants

with longer pods

produce new plants with longer pods.


They did an EXPERIMENT:


They planted seeds from short pods in Plot A

and seeds from long pods in Plot B.



They got RESULTS and ANALYSED the results:


Harvest from Plot A . . . . Harvest from Plot B



The seeds determine the size of the seed pods

. . . more or less.


They asked more QUESTIONS:

Why are a few of the seed pods

from Plot B short?

Did both plots produce the

same number of seed pods?

Is the taste of the mustard seeds the same?


Science is not just a list of ‘facts’!
Science is a process -
a method of questioning…
and finding answers to questions by
observing, hypothesizing, experimenting,
measuring, noting results, analysing,
reasoning, making conclusions,
communicating, re-questioning,
and revising conclusions.


There is a lot of variation
in the scientific method.

The order is not fixed,

and not all of these processes
are always included.


Some of our ancestors liked to eat

the young mustard leaves

that were packed closely together.


They were very tasty.



The farmers needed to collect seeds

to grow the next year's crop.

Instead of eating all the plants,

they let some plants grow

and produce flowers and seeds.


They wanted to get more plants

with tightly packed leaves,

so they selected seeds from the plants

that had started out with tightly packed leaves.


They planted these seeds the next year.



The new crop had more plants

with leaves packed tightly together.


Each year they selected seeds

from the plants with tightly packed leaves.


If all the best plants were eaten,

then the worst plants would be the only ones left

to produce seeds for the next year's crop.


After many years, what did they get?


Cabbage! (bandgobi)


Had one plant changed

from having less tightly packed leaves

to having more tightly packed leaves?




An individual wild mustard plant

did not change into a cabbage plant.


Plants that happened to have tightly packed leaves

were the ones that farmers selected for seeds.

The POPULATION of plants changed

after many generations of selection.


A population in which only a few plants

had tightly packed leaves

evolved into a population in which most plants

had tightly packed leaves.



In another place, people liked to eat the tightly packed,

undeveloped flowers of some mustard plants.

They were tender and sweet.


A few of the undeveloped flowers

went on to produce flowers and seeds.

The farmers gathered seeds from these plants,

and planted them the next year.


The seeds sprouted and the new crop grew.




This crop has more plants with larger

and better tasting undeveloped flowers.


At the end of the season,

the farmers again chose seeds from the plants

with the best undeveloped flowers.


After many years of sowing the seeds

from the plants with the tastiest undeveloped flowers,

look what they got.


Cauliflower! (phoolgobi)



In yet another place,

people found another kind of wild mustard.

Some of its roots were thick and juicy.


They tasted good.

So they planted the seeds from these plants.


Each year farmers saved the seeds that

gave plants with thick, tasty roots,

and they used them to plant the next crop.


After many years, look what evolved:


Radishes! (mooli)


That's not all -

over several thousand years,

farmers in different places have gotten

many varieties of plants

from the wild mustard family.



All of these were produced by people
selecting the kinds of plants they wanted.


Here ‘artificial’ means ‘produced by people’.


It is also called SELECTIVE BREEDING.



Sometimes people don’t get what they
want by artificial selection.


Sometimes a plant has larger roots
just because the plant got more water.
Seeds from these plants may grow
into plants with small roots the next
year, if they do not get so much water.

The size of the roots is not
determined just by the seeds.


Sometimes seeds from plants with
one desirable characteristic end up
producing new plants with some
unwanted characteristic.


For example, we may get a larger
cabbage, but it may be bitter.

One characteristic may affect
another characteristic.


Artificial selection is one of the
methods farmers and scientists
continue to use to produce new
kinds of plants and animals. By
selecting certain individuals for
breeding, we may be able to get
bigger potatoes, sweeter grapes,
faster growing wheat, cows that
give more milk, and chickens that
are healthier.


Once, some people said,
“We want mustard leaves that taste like mango!”

Do you think it is possible?

They looked everywhere for

a mustard plant that tasted like mango.

But they could not find a single mustard plant

that tasted even slightly like mango.

So, what could they do?
They could not get mustard leaves that
tasted like mango. They could only
develop variations that they happened to
find in nature.

Some said mango mustard was
a silly thing to want, anyway!



Now, suppose there were no people.

Could a similar thing happen without people?
Could wild mustard give rise to mooli without people?
Could it happen without intention?


Suppose once upon a time,
in a place without people,
there is a population of wild mustard.


As you can see,

in any population there is variation.

In this case some plants have large roots,

and others have small roots.
The plants with large roots produce seeds

that often give plants with large roots.

Those with small roots usually produce

plants with small roots.


The field often floods.

And almost all the mustard plants with small roots
get washed away...


And those with large roots remain.


What might happen after many years?


There might be more mustard plants
with larger roots!



Or, suppose there is
another field of wild mustard...



In this field, some insects come to live.


Suppose the insects eat large mustard roots,
but not small mustard roots.

Then, what might happen?


There might be more mustard plants

with smaller roots!

Here ‘natural’ means ‘not produced by people’.

The population of mustard plants evolved.
The change in the population may or may not

be a large or sudden change.

In this example, the change was not as large

as what the farmers got,

but the population of mustard did change.

Natural selection

is very different from

artificial selection.

In artificial selection,

farmers choose the kinds of plants they want.
In natural selection,

nobody chooses what they want.
There is no plan.
There is no design.


Did the mustard want to get large roots?
Do plants have desires?
What did the insects want?
Do insects have desires?

If the insects did have a desire,

they would have liked to have

more plants with larger, thicker roots

- but they got just the opposite.


In another case, a plant may evolve

that is a good food for a certain animal,

but it will not evolve

in order to be a good food for that animal.

“Training is everything.

The peach was once a bitter almond;

cauliflower is nothing but cabbage

with a college education.”
(Mark Twain, Pudd’nhead Wilson, 1894)


Organisms affect their environment

and the environment affects organisms.


For example, mustard plants remove nutrients from the soil.
When they die and decompose,
the plants also add nutrients and organic matter to the soil.
On the other hand, a flood may remove the nutritious topsoil.

Changes in the soil will affect the growth of future
generations, and may also make certain variants
more or less likely to survive and reproduce.

Many processes are interdependent and interconnected

with the process of natural selection.


When we do science, we find evidence
that natural selection really does happen,
and it causes evolution.

Evolution is the process by
which populations of plants,
animals, and other living things
change over generations.


Individual plants, animals, and
other organisms do not evolve.

Populations of organisms evolve.

If the change is great enough,

we say that a new species has evolved.


A population is a group of the
same kind of living things living in
the same place at the same time.
In every population there is variation.

No two individuals in a population are exactly alike.
Some of the differences can be passed on to

future generations (to some extent, they are heritable).


There are a number of mechanisms by which evolution occurs.
Here we have discussed only two ways:

People can change a population on purpose through artificial selection.
Natural selection does not happen on purpose.


You can’t always get what you want!


... more questions: Appendix


This is from the book "HOW DO THEY EVOLVE?" by Karen Haydock,

National Book Trust, New Delhi (2015) ISBN 978-81-237-7371-1

Hindi version: जंगली सरसों के उपहार, Eklavya, Bhopal (2017) ISBN: 978-93-85236-26-6

available as pdf