Re: Origins of vision

Posted on May 16, 2011 by Michael

I’m doing another repost, this time taking from an article I did about the origins of vision. Note that the quote coloring is reversed from how it normally appears.

Vision likely originated as simple eyespots in simple organisms. It also is traced back to jellyfish and their own simplistic eyespots, which are actually still present in some manner today. That is, jellyfish have areas of photoreceptor cells which don’t allow vision as we know it (they don’t even have brains), but they do allow a sensation of particular wavelengths of light to be perceived. These wavelengths often indicate depth (and maybe predators), which in turn may indicate food source (pelagic jellyfish don’t tend to get to plump).

Recent research has discovered the genetic pathway involved in light sensitivity in a close relative of the jellyfish.

“We determined which genetic ‘gateway,’ or ion channel, in the hydra is involved in light sensitivity,” said senior author Todd H. Oakley, assistant professor in UCSB’s Department of Ecology, Evolution and Marine Biology. “This is the same gateway that is used in human vision.”

This allows for a prediction using evolution: all organisms alive today which share a common ancestry with hydras will share this same genetic gateway. Organisms like flies, as the article points out, do not share this ancestry with vertebrates and as such do not share this genetic gateway. If they did share it, then wow. Creationists could actually trot out their improbability arguments.

“This work picks up on earlier studies of the hydra in my lab, and continues to challenge the misunderstanding that evolution represents a ladder-like march of progress, with humans at the pinnacle,” said Oakley. “Instead, it illustrates how all organisms — humans included — are a complex mix of ancient and new characteristics.”

(End different quote coloring.)

I looked this post up because I recently ran across a creationist who actually trotted out that old “the eye is irreducibly complex” bull and I was searching for some other links. But what’s interesting is what a different creationist was saying in the comment section:

You premised your claim of cnidarian relationship to vertebrates and humans on a gene they share in common. You said specifically, “This allows for a prediction using evolution: all organisms alive today which share a common ancestry with hydras will share this same genetic gateway.” I pointed out that certain beetles share certain genes with vertebrates and humans that other insects do not – and by your logic, that would mean these beetles share an ancestry with humans other insects do not.

As I pointed out at the time (and as the creationist failed to even come close to grasping), my claim was not based upon the sharing of individual genes, but rather on the sharing of complex genetic pathways. It is these pathways that ultimately allow for such a prediction. The creationist then confused the discussion on pathways with the article focus of a gateway. (I pointed out his error to him, but to no avail.) It is these pathways, by and large, which first get us to the point of where we can say that hydra and humans share a common ancestry in terms of vision. From that point we can look at the particular gateway in question and make the prediction I originally made. (One caveat: organisms which have lost their ability to see may not share the gateway.)

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Origins of vision

Posted on March 14, 2010 by Michael

Vision likely originated as simple eyespots in simple organisms. It also is traced back to jellyfish and their own simplistic eyespots, which are actually still present in some manner today. That is, jellyfish have areas of photoreceptor cells which don’t allow vision as we know it (they don’t even have brains), but they do allow a sensation of particular wavelengths of light to be perceived. These wavelengths often indicate depth (and maybe predators), which in turn may indicate food source (pelagic jellyfish don’t tend to get to plump).

Recent research has discovered the genetic pathway involved in light sensitivity in a close relative of the jellyfish.

“We determined which genetic ‘gateway,’ or ion channel, in the hydra is involved in light sensitivity,” said senior author Todd H. Oakley, assistant professor in UCSB’s Department of Ecology, Evolution and Marine Biology. “This is the same gateway that is used in human vision.”

This allows for a prediction using evolution: all organisms alive today which share a common ancestry with hydras will share this same genetic gateway. Organisms like flies, as the article points out, do not share this ancestry with vertebrates and as such do not share this genetic gateway. If they did share it, then wow. Creationists could actually trot out their improbability arguments.

“This work picks up on earlier studies of the hydra in my lab, and continues to challenge the misunderstanding that evolution represents a ladder-like march of progress, with humans at the pinnacle,” said Oakley. “Instead, it illustrates how all organisms — humans included — are a complex mix of ancient and new characteristics.”

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Eyespots

Posted on October 22, 2008 by Michael

History recently aired a series called “Evolve” which focused upon various aspects of evolution: wings, sex, guts, etc. But the most interesting episode was probably the one on eyes. It’s pretty clear they started out with eyes because of all the hub-bub made by creationists who find this organ to be too complex to have evolved by blind chance (what about the brain?). Natural selection is not chance (though it is blind – half credit), but such a misconception is one of the reasons eyes needed to be a starting point.

What History didn’t do, however, was get down to the cellular level of eye evolution. They may have touched upon photoreceptive cells, and that’s technically the cellular level, I suppose, but it overlooks an important aspect of evolution: everything which evolved today began its evolution (eventually) at the cellular level. So it is to my delight that I came across a Wikipedia article on eyespots.

Eyespot apparatus of euglena

Eyespots are a lot like they sound they are. They’re photoreceptive areas found in some plants cells (algae) and even in single celled organisms such as the euglena featured above. These are simply areas which cause a reaction to light – it becomes too bright, you may be too close to the surface. Swim away.

The advantage should be quite clear. The ability to detect light – not shape, size, dimension, or detail – gives an organism a lot of information about its environment. Specifically, History did address the eyespots of certain squids. These squids, only having nervous systems (no brains), would simply go into a sort of lull when coming near a certain wave length of light. As it not-so-coincidentally happens, that wave length corresponds with the wave length common near the food source of these squids.

Here’s the interesting kicker for which I think everyone should perk up: the origin of these eyespots works upon signal transduction, which is initiated by enzymes. This is what happens in every cell everywhere. Enzymes catalyze various things within cells. Lactase, for example, catalyzes lactose into galactose and glucose monomers – you drink milk, proteins (lactase) in your body will break it down into its constituents. It’s basic biology.

So how do new enzymes arise that can cause the formation of eyespots? This is a matter of a mutation within the DNA of a cell. Some “letter” of DNA is changed through some sort of error in copying. It happens all the time. You have 50-100 mutations in you right now (most, if not all, are probably neutral). DNA replication isn’t perfect. So a simply mutation can quite easily code for a new enzyme, which can cause the formation of an eyespot – the beginning of the eye. A slow, cumulative building through, perhaps, further mutation combined with the non-random action of natural selection can (and has separately over 40 times) evolve a complex eye worthy of fighting on the evolutionary stage of life.

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