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00:04 How did the eyes of spiders evolve?
00:11 Most spiders have eight eyes, although a few have only six.
00:15 Generally, they have two larger principal eyes, and the rest are secondary eyes.
00:21 They help give spiders almost 360-degree vision, which they need.
00:27 That's because spiders have no neck, so they can't turn their heads.
00:31 To see any predators or prey, they need to turn their entire bodies.
00:37 Jumping spiders need especially keen vision.
00:41 That's because their various sets of eyes do different things.
00:45 The front pair identifies detail and color,
00:48 helping it to determine whether a target really is potential prey.
00:53 And the secondary eyes calculate the distance to it and its direction of motion.
01:01 Other spiders, like yellow sac spiders, are nocturnal,
01:05 so they need to have good night vision.
01:09 When it comes to insects, scientists know quite a bit about how their eyes develop,
01:14 but so far, researchers haven't studied the eyes of spiders in as much detail.
01:20 In one study, biologists looked at spider embryos to see how their eyes develop.
01:27 First, they had to remove the tiny arachnids from their egg sacs.
01:32 The scientists were also interested in the genes that determine how spider eyes develop.
01:38 That included comparing their activity to the activity of genes
01:42 that determine eye development in other groups of animals.
01:46 There were a lot of similarities.
01:49 The researchers found that the same genes that determined the development
01:53 of other sophisticated eye structures in other animals
01:56 were also active in spider eye development.
02:00 They were involved, for example, in the development of the compound faceted eyes in insects.
02:06 These findings support the theory that the astonishingly diverse types of eyes
02:11 found throughout the animal kingdom
02:13 could potentially all be traced back to a common ancestor.
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