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You have about 20,000 genes in your DNA.

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They encode the molecules that
make up your body,

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from the keratin in your toenails,
to the collagen at the tip of your nose,

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to the dopamine surging around
inside your brain.

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Other species have genes of their own.

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A spider has genes for spider silk.

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An oak tree has genes for chlorophyll,
which turns sunlight into wood.

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So where did all those genes come from?


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It depends on the gene.

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Scientists suspect that life
started on Earth about 4 billion years ago.

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The early life forms were
primitive microbes

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with a basic set of genes for
the basic tasks required to stay alive.

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They passed down those basic genes
to their offspring

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through billions of generations.

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Some of them still do the same jobs
in our cells today, like copying DNA.

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But none of those microbes had genes
for spider silk or dopamine.

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There are a lot more genes on Earth today
than there were back then.

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It turns out that a lot of those
extra genes were born from mistakes.

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Each time a cell divides,
it makes new copies of its DNA.

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Sometimes it accidentally copies
the same stretch of DNA twice.

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In the process, it may make an extra copy
of one of its genes.

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At first, the extra gene works the same
as the original one.

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But over the generations, 
it may pick up new mutations.

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Those mutations may change how
the new gene works,

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and that new gene may duplicate again.

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A surprising number of our 
mutated genes emerged more recently;

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many in just the past few million years.

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The youngest evolved after our own species
broke off from our cousins, the apes.

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While it may take over a million years
for a single gene to give rise

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to a whole family of genes,

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scientists are finding that once 
the new genes evolve,

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they can quickly take on
essential functions.

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For example, we have hundreds of genes
for the proteins in our noses

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that grab odor molecules.

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The mutations let them grab
different molecules,

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giving us the power to perceive trillions
of different smells.

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Sometimes mutations have
a bigger effect on new copies of genes.

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They may cause a gene to make its
protein in a different organ,

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or at a different time of life,

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or the protein may start doing
a different job altogether.

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In snakes, for example, there's a gene
that makes a protein for killing bacteria.

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Long ago, the gene duplicated
and the new copy mutated.

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That mutation changed
the signal in the gene

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about where it should make its protein.

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Instead of becoming active in
the snake's pacreas,

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it started making this bacteria-killing
protein in the snake's mouth.

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So when the snake bit its prey,
this enzyme got into the animal's wound.

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And when this protein proved
to have a harmful effect,

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and helped the snake catch more prey,

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it became favored.

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So now what was a gene in the pancreas
makes a venom in the mouth

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that kills the snake's prey.

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And there are even more incredible ways
to make a new gene.

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The DNA of animals and plants
and other species

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contain huge stretches without any
protein coding genes.

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As far as scientists can tell,
its mostly random sequences

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of genetic gibberish that serve
no function.

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These stretches of DNA
sometimes mutate, just like genes do.

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Sometimes those mutations
turn the DNA into a place

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where a cell can start reading it.

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Suddenly the cell is making a new protein.

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At first, the protein may be useless,
or even harmful,

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but more mutations can 
change the shape of the protein.

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The protein may start
doing something useful,

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something that makes an organism
healthier, stronger,

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better able to reproduce.

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Scientists have found these new genes
at work in many parts of animal bodies.

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So our 20,000 genes have many origins,

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from the origin of life, to new genes
still coming into existence from scratch.

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As long as life is here on Earth,
it will be making new genes.