Why Did Evolution Do This?

Most animals have bllod which contains the iron compound hemoglobin. Its function is to carry oxygen in the blood, and it does so efficiently. However, some marine animals (like the horseshoe crab and the octopus) use a copper compound (cyanoglobin) to accomplish the same function. The copper-based blood is not as efficient, and these animals have less endurance because of it. My question: why woule evolution select such an inefficient means of carrying oxgen? Copper is a scarcer element than iron, and the iron compond works better.
So why do some animals still use the cyanoglobin?

Because it would cost too much, short-term, to tear down the whole plant and rebuild it to more “efficient” specs. And there is no good way to phase in the new methods gradually without causing loss of productivity in the transition process. As long as the older formulae work well enough to produce another generation of product, the systems will continue.

Natural selection works on a relative basis within species - versions whose changes yield a relative reproductive advantage shape the species more strongly by successfully breeding in more copies of that version. But these incremental changes are to the baseline version of the species.

Evolutionary processes aren’t necessarily driven to optimize a species in any particular aspect - if a change results in, or is associated with reproductive advantage, then it is more likely that said change becomes more prevalent in copies of the species as time goes on. But, generally speaking, these changes occur with respect to the existing template, and major shifts in biochemistry are rather unlikely.

By amazing coincidence I was reading about this this morning. From here http://en.wikipedia.org/wiki/Octopus

I don’t much care for the sentence structure at the end, but bottom line is they maintain that hemocyanin works better than hemoglobin for the environment octupuses live in.

Not my field of expertise, and I pass it along for whatever you think it’s worth.

Because they haven’t become extinct. There is no other answer.

Natural selection results in things that “work”, but does not guarantee perfection. Your question is framed as though ID were the mechanism for evolution-- ie, an agent thought out a solution in advance.

Or - try to divest yourself of the notion that evolution is in all species attempting to arrive at the perfect product. Evolution is the word for the changes that have occurred and will occur over time. Those species that exist today survived - somehow - ourselves, included. Whatever works, man. We’re not at the top of any scheme. Rather, we’re what’s left up to this point.

The first sentence is key. The second I don’t agree with. I didn’t read the OP as anthropomorphizing evolution that way. I think he’s just stuck on the idea that evolution does NOT produce perfection. Evolution produces “good enough” and as long as good enough IS enough to take the organism through its development to adulthood and mating, that’s as far as it has to go.

The idea that evolution produces organisms that are all at the very peak of efficiency for their niche is false, and that’s what the OP is tripping on.

Perhaps. I keyed in on this, specifically, for the second:

Evolution doesn’t “know” whether something is scarce or not.

True. But you could read that as realizing that a vital compound would be difficult to synthesize on a large scale over time if a component of that compound were scarce, thus causing developmental problems and leading to the extinction of that organism.

Think of evolution as operating like a blind person trying to find the highest point in a landscape. The likely strategy is to always move in the direction of steepest slope. Eventually, he will find a place where there is no such direction. There are at least three kinds of such stationary points: a true peak, a plateau or a saddle point. The latter two are unstable and he will eventually resume climbing just from random motions. The third is stable. But lacking vision, he will not find the highest point of all (except by fortunate chance). Well, evolution is blind in that way and you cannot expect it to find an absolute peak.

In fact, there are many ways in which human design is quite suboptimal. Consider the birth canal through the largest bone in the body; the way the optic nerve emerges in the front of the retina causing a blind spot; the poor design of the back (which probably has potential to improve). But evolution cannot and does not make sudden leaps, although it can happen relatively rapidly. If no cure or vaccine for AIDS is found, whatever genetic traits make a few people not susceptible to it would spread through the population in maybe only a few hundred generations.

And of course, there is always the possibility, mentioned in an earlier post that the copper based oxygen carrier is actually superior in the environment in which it evolved.

This is analogous to the old creationist trope, “If evolution were true, rabbits would be green.”

Well, no; because brown works, obviously. There’s no shortage of rabbits. That’s kind of like saying, “If evolution were true, rabbits would have wings and venomous fangs,” simply because those strategies have worked for other species. The basic philosophy of evolution, as it were–in this context–is, “If it ain’t broke, don’t fix it.”

The word you want is “hemocyanin”. How and why it evolved is not fully known at this time. Those animals that have it now have it for the same reason we have hemoglobin: their ancestors had it, and there has been no reason to change it. Whatever the adaptive reasons for hemocyanin evolving in the first place may have been, they are probably still in place.

Hemocyanin is found in most molluscs and some arthropods, and appears to have evolved at least 500 million years ago - indeed, it seems to have been established during the Cambrian explosion.

First-rate analogy there Hari.
The wrist is another example of half-assery. A ball-and-socket joint would be far simpler than the cluster of bits we have.

I have to disagree with that one. The “design” of the wrist is a marvel of complexity, allowing a wide degree of articulation and applied mechanical advantage of forearm muscles in hand movement that would not be possible with a simple ball-and-socket joint. Ball-and-socket joints also have to be significantly oversized and reinforced lest they wear out or be overstressed; note that elderly people often need replacement of hip or knee joints due to wear, but aside from damage or arthritis don’t typically have wear-related problems with the wrist-like structure of the ankle, despite its more compact size.

Darwin’s Finch (and others) have it correct: the reason that most arthropods and molluscs use hemocyanin for oxygen transport is because their ancestors did, and because it continues to be a viable mechanism for oxygen transport. If some kind of Intelligent Designer decided to swap out hemocyanin for hemoglobin, it would require some serious reengineering in the rest of the circulatory and respiratory structure to accomodate this.


Blue Bloods
Not all blood is red like ours; the octopus’s blood is blue. The blue color comes from hemocyanin, the copper-containing protein that binds oxygen in the octopus. Human blood is red because its oxygen-binding protein, hemoglobin, contains iron. In addition to being blue, octopus blood is a poor carrier of oxygen, which helps explain the animal’s sometimes apparent laziness. To cope with the low oxygen levels, the octopus maintains a constant high blood pressure and has three hearts. Two of the hearts pump oxygen-rich blood through the gills, while the third circulates it through the rest of the body.


OMG, I hadn’t thought about that. It is now clear to me that God must have created horseshoe crabs, because only God would use something that is non-optimal.

Except for those things that are optimal, which is clear evidence of the power, grace, and omniscience of God.


Given that horseshoe crabs go back in time to something like a bajillion years ago, I’m going to venture that they can reproduce/survive.

I mean, this is just a guess… but I am pretty sure that it works.

I will avoid all the issues that are killing me inside, such as implications that evolution does anything and design and all that.

Hmm. The planet Vulcan is hot, but with a lower oxygen pressure than Earth (as confirmed by several eps and movies, such as “Amok Time”). Maybe Vulcan was once colder?

In other words, a natural manifestation of Harvey Leibanstein’s concept of X-inefficiency? Never thought of it that way, but it makes sense…