Like in the eye for example how do the cells know to start curving around into an orb. How do the ones in the eyelid know that it’s the last one and doesn’t grow to big or too small of a eyelid?
In: Biology
[Morphogens](https://en.wikipedia.org/wiki/Morphogen)
When an embryo develops, new structures form as follows. A cell or group of cells at the right spot produce a chemical called a “morphogen” that diffuses (spreads out) a bit and so mark the area where the structure should form,
So, in your example, some morphogen the signals “skin cells needed here” tells all the cells growing there that they should turn into skin cells. And the cell at the border of the eye lid noticed that it should be the last cell to do so because it only gets very little of the morphogen.
Of course, this is all a complicated machinery, because some morphogens will cause other cells to turn into morphogen-producing cells, and some things only happen if different morphogens coming from different directions meet at the right concentration ratio and so on.
They don’t “know” anything. The cells simply are, and the ones in the eye have physical characteristics that lead them to forming a sphere when many are brought together (though actually it’s many types of cell all working together – though without knowing that they’re doing so).
They have no awareness, just like wood doesn’t know that it’s “supposed” to set on fire when you hold a match under it. This might so sound like a nice coincidence, but in fact it’s the other way around – we burn wood precisely because it sets on fire when you hold a match under it. Perhaps other creatures evolved to have eyes that were squares but they died out because they couldn’t turn in their socket.
(They didn’t, btw, but it’s just an example to show that what we consider to be simply “the way things are” is the result of us witnessing what we see around us. The vast majority of these physical characteristics that manifest themselves around us go without us even thinking about it – grass is green, sticks are brown, water is transparent, rocks are hard, hair is thin etc – they are how they are due to the cells that make them up. There was no way they were going to be otherwise.)
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