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You have about 20,000 genes in your DNA.

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They encode the molecules that[br]make up your body,

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

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to the dopamine surging around[br]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,[br]which turns sunlight into wood.

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So where did all those genes come from?[br]

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It depends on the gene.

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

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The early life forms were[br]primitive microbes

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

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They passed down those basic genes[br]to their offspring

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through billions of generations.

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

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

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

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

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

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Sometimes it accidentally copies[br]the same stretch of DNA twice.

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

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

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

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Those mutations may change how[br]the new gene works,

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and that new gene may duplicate again.

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A surprising number of our [br]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[br]broke off from our cousins, the apes.

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While it may take over a million years[br]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 [br]the new genes evolve,

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they can quickly take on[br]essential functions.

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

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that grab odor molecules.

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The mutations let them grab[br]different molecules,

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giving us the power to perceive trillions[br]of different smells.

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

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They may cause a gene to make its[br]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[br]a different job altogether.

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

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Long ago, the gene duplicated[br]and the new copy mutated.

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That mutation changed[br]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[br]the snake's pacreas,

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

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

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And when this protein proved[br]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[br]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[br]to make a new gene.

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The DNA of animals and plants[br]and other species

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contain huge stretches without any[br]protein coding genes.

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As far as scientists can tell,[br]its mostly random sequences

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of genetic giberish that serve[br]no function.

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

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Sometimes those mutations[br]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,[br]or even harmful,

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but more mutations can [br]change the shape of the protein.

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The protein may start[br]doing something useful,

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something that makes an organism[br]healthier, stronger,

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better able to reproduce.

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Scientists have found these new genes[br]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[br]still coming into existence from scratch.

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