The article is about vertebrates, not about animals in general. The vertebrates originally had at least 3 eyes, 2 lateral eyes and one in the middle of the hea

The article is about vertebrates, not about animals in general. The vertebrates originally had at least 3 eyes, 2 lateral eyes and one in the middle of the head. Most vertebrates of today have lost the median eye, though there are a few species, like tuatara, which still have it. The research reported in the article has shown evidence that the retina of the lateral eyes of the vertebrates has evolved not from the original retina of those eyes, but from the retina of the middle eye, which had a different structure, i.e. different photoreceptors.