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I've always thought - and this is just a guess - that, like sex feeling really good makes you want to do more of it and in turn continue the human race, so too does laughter make conversations enjoyable and helps promote dialogue between people. If sitting around a campfire and talking only included boring, or angry, or pointless conversations, then there would be no fun, or good feeling, in sitting around conversing.But conversing is how we also spread information. Critical information. So we need to talk. Maybe laughter from dialogue helped us want to talk.- Oni

For humans, yes. But the protein that makes up finger nails is also found in birds and amphibians, along with reptiles and mammals, like Huntard pointed out.See here:

quote:

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Keratin filaments are abundant in keratinocytes in the cornified layer of the epidermis; these are cells which have undergone keratinization.

• the -keratins in the hair (including wool), horns, nails, claws and hooves of mammals
• the harder -keratins found in nails and in the scales and claws of reptiles, their shells (chelonians, such as tortoise, turtle, terrapin), and in the feathers, beaks, claws of birds and quills of porcupines. (These keratins are formed primarily in beta sheets. However, beta sheets are also found in -keratins.)

Arthropods such as crustaceans often have parts of their armor or exoskeleton made of keratin, sometimes in combination with chitin.

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The baleen plates of filter-feeding whales are made of keratin.

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It can be integrated in the chitinophosphatic matter that composes the shell and setae in many brachiopods.

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Keratin is also found in the gastrointestinal tracts of many bioforms, including roundworms (which also have outer layers of keratin).

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Although it is now difficult to be certain, the scales, claws, some protective armour and the beaks of dinosaurs would, almost certainly, have been composed of keratin

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- Oni

Here's an easy to follow link: Washington.Edu Or this one too: positscience- Oni