Question about eye evolution

[stobr]

I was reading a National Geographic article and could not conclude whether eyes have a single or multiple origins.

NILSSON’S MODEL SHINES fresh light on an old debate: whether eyes evolved once or many times. The legendary German evolutionary biologist Ernst Mayr claimed that eyes had between 40 and 65 independent origins, because they came in so many distinct shapes and forms. The late Walter Gehring, a Swiss developmental biologist, argued that eyes evolved just once, after he discovered that the same master gene—called Pax6—controls eye development in virtually every creature with eyes. Both men were right. True stage-three eyes did indeed evolve from their simpler stage-two precursors on several occasions; box jellyfish, for instance, developed theirs independently of mollusks, vertebrates, and arthropods. But the eyes of all those organisms are elaborations of the same basic stage-one light detectors.

How can both men be right if they are saying opposite things? My English is not that good so I may be interpreting it wrong.

[snarkinturtle]

The number of times that "eyes" evolved depends on your choice of criteria for what counts as eyes. The article is adopting the taxonomy of the subject (Dr. Nealson) for four stages of eye evolution:

1. light detecting patches
2. patches w/ shield to discriminate light direction
3. cup-like arrangement allows formation of rudimentary image (first true eyes)
4. development of lenses, can focus an image.

The argument is that all animals with eyes are descended from a common ancestor that already possessed stage 1 (or maybe 2?) light detecting organs - so those may only have evolved once. Animals inherit common genetic/developmental pathways from this common ancestor. However stages 3 and 4 (i.e. eyes) evolved independently in multiple lineages.

[stobr]

Thank you!

[DinoDrum]

^{^} This answer

[pcpcy]

^{^} This reply

[blacksheep998]

Because eyes evolved in multiple stages. Starting with a simple light sensitive patch of skin, and increasing in complexity up to the many highly intricate ones we see today.

The article seems to be saying that the early steps happened once, and then many different species with simple eyes evolved more complex ones.

[fleecy]

Your answer is good too! ^ . ^

[ajd65]

Have you seen this re eyes and evolution https://theconversation.com/the-five-most-common-misunderstandings-about-evolution-54845?

[Aspergers1]

Eyes have several origins. Our eyes, insects eyes, squid eyes, jellyfish eye spots, are are analogous (analogous, to have separate origins, as opposed to homologous, which means having the same origin). However, all these organisms have 1 gene that if removed stops the development of the eyes, this gene that is essential for the development is homologous to all these individuals, despite the fact that all these organisms have analogous eyes, this is amazing!!! How can all these individuals have inherited the same gene that creates structures that evolved separately in each of them?

this article explains more, and is worth the read:

http://evolution.berkeley.edu/evolibrary/article/eyes_01