The reasons you have eyelashes

I had always assumed that eyelashes evolved simply to keep particulate matter out of the eyes. Now a study published in the Journal of the Royal Society Interface reports that particulates are only half the story; eyelashes also divert airflow to prevent drying of the eyes.

Through anatomical measurements, we find that 22 species of mammals possess eyelashes of a length one-third the eye width. Wind tunnel experiments confirm that this optimal eyelash length reduces both deposition of airborne particles and evaporation of the tear film by a factor of two. Using scaling theory, we find this optimum arises because of the incoming flow's interactions with both the eye and eyelashes.

And this bit from the introduction was an interesting TYWK:

One study found that growth of eyelashes occurs in response to exposure to allergens. Children with allergies have 10% longer and denser lashes than those without allergies. This response arises from allergens triggering mast cells within the inside of the eyelid to release prostaglandins that promote hair growth, which presumably protects the eye.

More at the link, with additional discussion at the L.A. Times, via The Presurfer.

Previously on TYWKIWDBI:
Poliosis, and
Elizabeth Taylor's distichiasis (top photo).