Evolution question

I know this sounds counterintuitive, but are there any organisms that have decreased in complexity as their species evolved? Second question, can you name any organism that evolved any traits or characteristics that ultimately proved detrimental?

Whales have gone from the sea to land and back to the sea,in the process they lost there legs. Lots of species have adapted to an enviroment only to have the enviroment change later,this is one reason why species go extinct.

you see evidence of evolved death-traits all the time, many spontaneous miscarriages are because the fetus is unfit. evolution is more luck than design.

  1. Mycoplasma may have evolved from more complex forms.
  2. Many species of birds evolved pretty feathers on their heads. Humans, desiring these feathers, hunted many species to extinction. That’s about as detrimental as a trait can get.

Human beings and sickle cell anemia. It evolved as a protection against malaria. Move a population with the sickle cell gene out of an environment where malaria is common and the trait becomes detrimental.

Blind cave fish. They have non-fuctional, vestigial eyes which show they evolved from an ancestor which could see but lost the ability to see when they no longer needed it. I suppose you could call that a decrease in complexity.

Evolution always seeks whatever will give a reproductive advantage in the immediate environment. It never will select for something that’s immediatly detrimental, but there are countless examples of traits which were advantageous at one point but turned out to be a major liability when the environent changed.

The dinosaurs. That comet hit, they were too set in their ways to adapt, game over. You can see animals and plants being pushed out by imported species all the time, all over the world, because they’re not able to adapt quickly enough.

Sickle-cell anemia is an interesting example, but far more commonplace would be homosexuality, which is a dead-end evolutionary trait because it does not encourage reproduction (no moral judgment expressed or implied). However, it is only a trait, and the remaining breeding population is sufficient to keep the species going. In another thread (I forget which one) some reader expressed surprise that some high percentage of humans (I think it was about 30% in one study) simply didn’t like sex, or didn’t like it all that much. Even if this figure was accurate (or higher) a reasonably robust species like homo sapiens sapiens can carry on. An evolutionary trait that killed off a portion of a species population (or kept it from breeding) just encourages increased breeding in other corners.

Unfortunately, the same dynamic occurs in bacteria when confronted by antibiotics.

By what objective criteria do you measure complexity? The theory of evolution does not require that later organisms be more “complex” than earlier ones. Parasites, with the tapeworm being a prime example, can be largely nothing but a digestive and reproductive system inclosed within a membrane.

One celled organisms exists side by side with those having multi-cell structure. A virus is mostly DNA or RNA with an ability to move and means to get into cells and take over their functions so as to generate more viruses.

The key to evolution is that the organism is suitable for survival and reproduction in its environment.

I don’t know enough details of the evolutionary record to identify particular organisms that have died out from a fatal flaw. However, specialization when carried to extremes seems to be detrimental. When there is a shift in environment, the organism is unable to cope with the change and dies out.

For more details try http://talkorigins.org/

A “decrease in complexity” could be something as simple as a reduction in the number of “parts”: both Perissodactyls (e.g., horses, rhinos) and Artiodactyls (e.g., deer, pig) have a reduction in the number of digits (taken to the extreme in horses, with but one finger/toe on each limb). Many cursors (animals who can run fast) have fused radii and ulnae in their forelimbs.

Theropod dinosaurs had a reduction in the number of digits in their forearms (relative to the ancestral condition), and a reduction in the number of toes. Birds have taken the finger reduction even further, having but one “finger” and a “thumb” on each hand.

Such “simplification” can have a tendancy to create specialists, which in turn restricts the available environments in which an organism can function (which can, in turn, leave them more susceptible to extinction). Generalists (like humans) tend to retain more of their ancestral features, and may appear more “complex”.

But, as David Simmons points out, “complexity” is really a subjective concept. Parasites are very good at what they do, despite their apparent anatomical simplicity.

Our way back ancestors had 7 bones in the jaw, we have 1. Something interesting happened to the other 6. And then there’s our tail…

Go back far enough and our ancestors had neither jaws nor tails…

There was probably a time when the human appendix solved more problems than it created. But as long as it doesn’t kill a conspicuous number of people before they reach maturity, we’re stuck with it.

Well, barring futuristicky genetic engineering, which one could argue is part of our evoluntionary process.

I don’t have any specific examples of overspecialization leading to extinction, but I do know that there are cases in the record.
In regards to the first question in the OP, two points. One: evolution does not have a “direction”, contrary to many popular interpretations. As Darwin’s Finch pointed out, evolution produces organisms more suited to their environment, whatever level of simplicity or complexity is required. There is no inevitible progression towards complexity or “higher” organisms.
As counter-examples, many parasites have lost complexity in their evolutionary history. Rhizocephalans parasitize crusteceans and evolved from barnacle-like ancestors. In the process they have lost almost all internal and esternal structure, and the adult of some species consists of little more than a brood-sac and some roots. For more on this creature, and the questions of the OP, see Stephen Jay Gould’s Leonardo’s Mountain of Clams and the Diet of Worms

There is nothing in the theory of evolution that dictates evolution must be from (structurally) simple to complex. For example, human have lost the ability to consciously move the outer ear, but occasionally a mutation allows certain individuals to partially regain that ability. A horse, for example, have far better control.

The correct answer to this question, by the way, is “all of them.” Extinction for a species, just like death for individuals, is inevitable.

The average “life expectancy” of a species is around 10 million years (IIRC).

Didn’t snakes used to have legs?

And no, this isn’t an attempt to inject religion into this thread.

Yep. So did whales, many of which still have vestigial leg bones beneath their skin.

Well, unless you’re seeking to start a contentious theological debate, design doesn’t come into it at all. No designer.

I would recommend another Stephen Jay Gould book, Full House: The Spread of Excellence from Plato to Darwin, which directly addresses the misconception that evolution has a direction (and he uses the same arguments to explain why no one bats .400 in the major leagues anymore).

Actually, I would probably recomment any book by Gould. So just go to Amazon and buy them all.

– CH

Sickle cell did not “evolve as a protection to malaria”

Like all mutations, it showed up completely by accident. It is preserved in the population because of two factors. One, it is a recessive trait, which means that someone can ‘carry’ it, without being affected. Carriers of sickle-cell are ‘half-sick’, because half of the time, the gene for sickle hemoglobin is transcribed resulting in production of the defective protein and the other half of the time, the normal hemoglobin is produced. This is what causes the resistance to malaria. Two, it increases the chance of reproducing in areas where malaria is prevalent because those people who do not carry the gene are likely to die from malaria before reproducing.

Remember, evolution is driven by reproductive success. That’s why ‘diseases of old age’, even when caused directly by genes, persist in the population… because they don’t prevent people from reproducing. Those diseases ‘evolved’ as well, and they would be considered ‘detrimental’ from the standpoint of quality of life, but from the evolutionary standpoint, they are meaningless because they do not affect reproductive ability.