Did herbivores come first?

[dichotomy]

I'm glad about that. But that wasn't what I was reacting to. It was your statement "What this is sort of telling me, I think, is that unconscious life doesn't think in terms of animal, mineral or vegetable, it thinks in terms of what available nutrients can I use."

 

It was the use of the word "thinks" that prompted my response. That "think" does mean a conscious choice, doesn't it?

 

If you want to avoid the confusion in the future, do not use the word "think" when talking about evolution; there is no "thinking" involved on the part of organisms.

 

Ok, so you’re hypersensitive to ‘convenient shorthand’, got it.

 

I should have stated something along the lines of - Life uses whatever available energy there is available in order to survive?

 

Cnidaria are the most primitive animals with neurons, as far as I know.

 

Sponges are the most primitive animals around now. How they emerged isn't completely clear, as they have different cells types that line up with different protists. The most obvious in that choanocytes match up very well with choanoflagellates, and this has been the most likely origin for a long time. But it isn't set in stone.

 

Here's a story on jellyfish possibly being the first. Or, first to diverge?

 

http://www.sciencedaily.com/releases/2008/04/080410153648.htm

 

"While cautioning that additional studies should be conducted to corroborate his team's findings, Dunn says that the comb jelly could only have achieved its apparent seniority over the simpler sponge via one of two new evolutionary scenarios:

 

1. the comb jelly evolved its complexity independently of other animals, after it branched off onto its own evolutionary path; or

the sponge evolved its simple form from more complex creatures

 

2. a possibility that underscores the fact that "evolution is not necessarily just a march towards increased complexity," says Dunn. "This scenario would provide a particularly dramatic example of that principle."

[lucaspa]

Ok, so you’re hypersensitive to ‘convenient shorthand’, got it.

 

Using "thinks" is not the "convenient shorthand". The shorthand is "the comb jelly evolved ..." (from your source below). When you add "think" you are out of the convenient shorthand.

 

I should have stated something along the lines of - Life uses whatever available energy there is available in order to survive?

 

This still implies choice: the individual is choosing to use the energy to survive. A better phrase would have been "species will diversify by natural selection to exploit available resources"

 

Here's a story on jellyfish possibly being the first. Or, first to diverge?

 

http://www.sciencedaily.com/releases/2008/04/080410153648.htm

 

You didn't quote the most interesting part of the article:

"Among the study's surprising findings is that the comb jelly split off from other animals and diverged onto its own evolutionary path before the sponge. This finding challenges the traditional view of the base of the tree of life, which honored the lowly sponge as the earliest diverging animal. ...

But even after Dunn's team checked and rechecked their results and added more data to their study, their results still suggested that the comb jelly, which has tissues and a nervous system, split off from other animals before the tissue-less, nerve-less sponge.

 

Now, remember that these are preliminary studies, and Dunn does caution "that additional studies should be conducted to corroborate his team's findings"

 

But let's assume, for discussion, that the findings hold up in the future. Since the comb jelly has tissues and a nervous system, does that mean that the basal multicelled animal had these?

 

Dunn goes into the 2 possibilities:

1. "the comb jelly evolved its complexity independently of other animals, after it branched off onto its own evolutionary path" IOW, the ancestor did not have tissues and a nervous system but now the descendents do because of independently evolving them, not getting them from an ancestor.

 

2. "the sponge evolved its simple form from more complex creatures ... a possibility that underscores the fact that "evolution is not necessarily just a march towards increased complexity," says Dunn. "This scenario would provide a particularly dramatic example of that principle."

 

What is under #2 we should keep in mind more often. We (and by this I mean evolutionary biologists, too) often tend to think that the current primitive species must be descended from equally primitive ancestors. That doesn't have to be true. Perhaps the ancestor of the sponge did have tissues and a nervous system. As the sponge lineage evolved toward a simpler ecological niche (exploiting an empty niche of a sessile animal), the complex structures represented energy to develop that wasn't needed. An evolutionary cost instead of a benefit. Therefore individuals without those tissues did better -- because they didn't have the cost of making the tissues -- and outcompeted them in the new niche.

[dichotomy]

What is under #2 we should keep in mind more often. We (and by this I mean evolutionary biologists, too) often tend to think that the current primitive species must be descended from equally primitive ancestors. That doesn't have to be true. Perhaps the ancestor of the sponge did have tissues and a nervous system. As the sponge lineage evolved toward a simpler ecological niche (exploiting an empty niche of a sessile animal), the complex structures represented energy to develop that wasn't needed. An evolutionary cost instead of a benefit. Therefore individuals without those tissues did better -- because they didn't have the cost of making the tissues -- and outcompeted them in the new niche.

 

 

Yes, I found #2 interesting because I've not come across that possibility before. I assumed there would simply be a die off, rather than a reduction in complexity.

[SkepticLance]

To dichotomy

 

Evolution to a simpler form to save energy is a common strategy. It is especially common among parasites. Because they live in a place surrounded by food, they do not need lots of the paraphenalia of life for those who are non parasites, and they lose the extra over time.

 

There is a bacterium called Mycoplasma genitalium which has lost most of its genome since it is parasitic. Viruses may be bacteria-like organisms that have lost most of their genes. Tapeworms are simplified.

 

Even humans have evolved to lose complexity in one way - our alimentary canal is the smallest for its size of any primate - probably a response to the lesser digestive demands of eating cooked food.

[lucaspa]

Yes, I found #2 interesting because I've not come across that possibility before. I assumed there would simply be a die off, rather than a reduction in complexity.

 

It is mentioned in any evolutionary biology textbook. Remember, each trait comes with a benefit and a cost. Think of antibiotic resistance in bacteria, particularly those that synthesize beta-lactamase to deactivate penicillin. Yes, it works in an environment where there are antibiotics, but it means the bacteria is spending energy to make an additional enzyme. When the antibiotics are removed, those strains are at a competitive disadvantage because their "complexity" is using more energy than is needed.

 

"loss of traits" is common. In addition to the examples SkepticLance gave, think of the blind mole rat that no longer has eyes, birds whose ancestors had teeth, and whales whose ancestors had legs.

 

BUT (and in biology there is usually a "but") "complexity" is sometimes a tricky word. Because natural selection can only add information, not subtract it, many of those traits lost come at the expense of additional "complexity" at the level of genes. For instance, in the blind mole rat, the loss of the eye is not indiscriminant, but rather the addition of tanscription factors that suppress the development of most of the eyes, but keep some minor parts of them for circadian rhythms: 6. J Diamond, Evolving backward. Discover 19: 64-71, Sept. 1998.

 

However, SkepticLance's example of Mycoplasma genitalium is a true loss of genes as it earns its life as a parasite. As SkepticLance said, viruses may also be a product of the same type of evolution.

[dichotomy]

 

However, SkepticLance's example of Mycoplasma genitalium is a true loss of genes as it earns its life as a parasite. As SkepticLance said, viruses may also be a product of the same type of evolution.

 

Ok, so a true loss of complexity is really defined by a loss of genes and not by inactive, or, switched off genes? Something like a whale developing fins where legs used to be would not be considered a true loss of complexity?

[lucaspa]

Ok, so a true loss of complexity is really defined by a loss of genes and not by inactive, or, switched off genes? Something like a whale developing fins where legs used to be would not be considered a true loss of complexity?

 

I have not seen an evolutionary biologist talk about "true loss of complexity". As I said, in biology "complexity" is a very loose term. We see it a lot from IDers as tho it is "real", but they don't define it either.

 

In the whales, the tail fin is not a replacement for legs. Remember, many whales still develop rudimentary bones of the pelvis and legs. The forefins are modified forelimbs, but they have all the bones of the land-dwelling forelimb. So I don't see that as any type of "loss of complexity" but rather "modification for a new function".

 

The sequence to a loss of genes seems to be quite long. First there is supression of expression of the gene. That stretch of DNA now has no function and can be mutated without affecting the individual. Since the gene isn't expressed any mutations are hidden from natural selection. It seems to me (and we will have to do some checking to see if I am correct), there are two basic outcomes (and maybe many more shades of those outcomes):

 

1. If it gets turned on again it will have a new function. That function could be either beneficial, neutral, or deleterious (depending on the function and environment).

 

OTOH, if not expressed that stretch of DNA does represent an energy cost during reproduction: individuals without that stretch would not have to expend so much energy.

 

2. So if there is a mutation that eliminated the DNA sequence it would be a selective advantage.

 

However, addition of a suppressor represents new DNA and new complexity: don't do what you are programmed to do.

[SkepticLance]

Following on from lucaspa.

 

It would seem that a 'loss of complexity' is better seen simply as a particular evolutionary development in response to environmental conditions. A parasite becomes 'less complex' because that is advantageous in that environment. The 'loss of complexity' is an evolutionary movement forwards in a different direction, rather than evolution backwards.

[NicholasConners]

Let's break it down. You can not have a food chain that starts with a predator. There would be nothing for that predator to eat. Even if the predator happens to be a single or multi-celled microbial piece of life. I'm inclined to believe the possibility that it was initially plant material that formed, then life that absorbed nutrients from that, and over time life that devoured the plant absorbing life. Giving rise to the food chain and evidently the moon pie.

[SkepticLance]

To Nicholas

 

Depends on your definition of 'plant.' Technically, plants are eucaryotes, which did not evolve till 2 billion years ago, with their predecessors - the procaryotes evolving 1 to 2 billion years earlier.

 

The first life almost certainly used material made by non organic processes, such as geothermal, as a source of energy and nutrients. Did this make them plants? Not by any definition I have seen.

 

The first photosynthetic organisms were early versions of cyanobacteria - but were not plants. Their appearance is marked by oxygen in the atmosphere, which shows in the fossil record as iron oxides. They probably came about 200 to 500 million years after the first living organisms.

[NicholasConners]

To Nicholas

 

Depends on your definition of 'plant.' Technically, plants are eucaryotes, which did not evolve till 2 billion years ago, with their predecessors - the procaryotes evolving 1 to 2 billion years earlier.

 

The first life almost certainly used material made by non organic processes, such as geothermal, as a source of energy and nutrients. Did this make them plants? Not by any definition I have seen.

 

The first photosynthetic organisms were early versions of cyanobacteria - but were not plants. Their appearance is marked by oxygen in the atmosphere, which shows in the fossil record as iron oxides. They probably came about 200 to 500 million years after the first living organisms.

 

Ah yes. Thanks for reminding me. I often forget how late most plant life bloomed. My head usually sticks in the Dinosaurian eras. This wouldn't ruin the food chain idea however. With a slight change from plant life to the minerals generated or provided by thermal vents in the ocean or primordial soup.

[pioneer]

At night when plants are not using photosynthesis they use the plant materials they collected during the day as an energy source. They are night herbivores. They are able to collect more than they use so we often think in terms of the net affect. If you took a potted plant and placed it in total darkness it will stretch as it cannibalizes plant material.

 

The first life was animal and dependent on the simple molecules from which life had assembled, as its food source. They were omnivores. Photosynthesis evolved from this. Once plants produced more food then they could use, plant predators began to appear. When these plant predators became too plentiful, then carnivore predators appeared to complete the food chain. The original carnivore predators may have been omnivores by default They had poor sensory systems and just opened their mouth and swam. After getting enough plant predator in their diet they developed a taste for it and genetics began to change.

[SkepticLance]

Actually, the first life was neither animal or plant. The dichotomy of animal/plant does NOT cover all life forms. It is better to leave all Bacteria and Archaeans out of that classification. Yet they are life, and they precede both animals and plants in that they arose earlier in evolution than either.

[CharonY]

Of course. Plants and Animals are different kingdoms within the domain of eukaryotes. That leaves out prokaryotes by default according to Woese's system. To be honest, I am not that familiar anymore of the most recent consensus on classifications on that level (or whether it has been resolved at all). When I studied protista were still used as a taxon, although they were not monophyletic. Rather recently I think there was another proposition in which the eukarya were not only grouped into plants, animals, fungi, and one or several protists group, but in six clusters existed. I actually forgot the names, but according to my memory (so take it with a big chunk of salt), the groups were basically animals and fungi in one group, plants and red as well as green algae in another, then there was group consisting of other algae and finally three groups of mostly or exclusively single cell organisms.

[dichotomy]

The original carnivore predators may have been omnivores by default They had poor sensory systems and just opened their mouth and swam.

 

 

That sounds like a modern day politician.