Thread: Evolution Spurts

What are evolution biologists' explanation for the evolution spurts that happened at the border between the eras/ages/periods? the absence of fossils of bridging species is i think 'cause there were relatively fewer animals to become fossils. no hand of god there. but what caused them? maybe an evolution gene? or a sporadic solar cycle yet to be identified that caused more mutations than usual? is there an accepted theory for it yet?

Though I don't know the exact theories off the top of my head, I'm pretty sure that most of the major diversifications of life have been studied and have accepted theories for their causes. It's usually due to a major environmental factor (e.g., oxygenation of the atmosphere), and/or the evolution of a key trait to take advantage of environmental niches that most animals were previously unable to exploit (e.g., the advent of terrestrial tetrapods). Try doing a search for on the Cambrian explosion. I would, but I'm at work and shouldn't be on this forum right now as it is :P

Try doing a search for on the Cambrian explosion.

thanks, i'll do that. I was also thinking of another thing. lets say you bury a bull terrier and a husky. would one recognise them as the same species if their fossils were discovered a few MY from now? i am wondering, because I once read a book where the guy talked about what might happen if, maybe, a large asteroid or such hit us and caused a major extinction. He used rats and mice and illustrated some possibilities of how they might change physicaly as they filled new niches. The wide variety of dogs have been bred in about 10000 years I think, so maybe such large extinctions could trigger large physical changes in geneticaly similar animals within a short period? then they could become distinct species as time goes by?

Originally Posted by KALSTER

lets say you bury a bull terrier and a husky. would one recognise them as the same species if their fossils were discovered a few MY from now?

well, assuming that all modern knowledge of dogs doesn't last a few MY into the future and there was no other way to tell, maybe not. Dogs are the most variable species alive today, thanks to strong human-imposed selection.

Originally Posted by KALSTER

The wide variety of dogs have been bred in about 10000 years I think, so maybe such large extinctions could trigger large physical changes in geneticaly similar animals within a short period? then they could become distinct species as time goes by?

basically, yes. so long as barriers to cross reproduction arose that allowed the different varieties to continue to diverge from each other, they would probably become distinct species from each other.

The Cambrian explosion is maybe not a very good model. It was probably not that explosive as people once thought. Molecular clock evidence certainly seems to back that up, and also the revelations at the other 2 sites that contain the fossils of soft bodied elements besides the Burgess Shale, make famous (as in popular) by SJ Gould's 'wonderful life'.

A better example is the rapid radiation of the Cichlids in lake victoria and neigbouring lakes.

Yes, the Cichlids are very interesting. What was striking, is how diverse there diets are. What would you say is required for any animal species to change from, say, plant eater to insect eater? Is it mostly intestinal bacteria? Is it possible for an animal to start out as herbivore, start mixing it's diet and eventually be able to digest insects later in life? or maybe they could slowly build up the symbiosis with bacteria over a few generations, passing on the intestinal bacteria from parent to child as usual? Very interesting.

i think the diet change would be largely evolutionary.
the change would be from herbivore-omnivore-carnivore, and back.
smaller an shorter-lived species with a high birth-output are better at adapting to new environmental changes, because of the larger potential genetic diversity in a shorter timespan.
hmm.. the smallest species are actually our genetic blueprints! or genetic ancestors. hmm how to say... grrr, easily confused.
just think about it, labrats, mice, they are all used because of their genetic similarity to us, and they have incredible adaptability.
i'm sure if nearly all life was destroyed, a special set of super-adaptible "blueprint animals" would be able to repopulate earth again.

Originally Posted by dejawolf

just think about it, labrats, mice, they are all used because of their genetic similarity to us,

Just keep in mind that lineage that gave rise to the modern rodents and the lineage that eventually gave rise to us split up 75 million years ago.

All modern rodents and humans have 75 million years of separate evolution under their belt.

rodents are used because they are mammals, easy to keep, relatively cheap to keep, have large sets of offspring.

If we had been aiming for genetic simularity we would have gone for the chimp. But the ancestor of the modern chimp and modern human still have undergone 6 million years of separate evolution..

Radiation follows mass extinction, and the logical extrapolation is that radiation is a direct result of the sudden availability of many new niches, perhaps combined with other factors such as reproductive isolation (as a byproduct of mass extinction and lower numbers etc) and so on.

I could be very wrong.

If i'm not mistaken, dogs have changed from carnivore to omnivore. That might have happened quite neer to their domestication. So what other differences are there between carnivore/omnivore/herbivore? I can think of the source of vitamens and micronutrients, any others? Anything that would slow down the transition between feeding habits, like fisiological changes that need happen? Again, intestinal bacteria probably play a huge role.

A big difference between carnivores and herbivores is intelligence. Carnivores tend to be smarter than herbivores, because hunting down another animal isn't as challenging as finding some grass to chew on. I'm not saying there aren't smart herbivores, like monkeys, but all carnivores need a certain level of intelligence in order to capture their prey that isn't necessary for a herbivore.

I'd say that in a situation where most of life have been wiped out, alot of opportunities would open up where intellegence is not as vital? An animal that changed to an omnivore, could still keep close to it's herbivore origens, but still be able to take advantage of opportunistic meals like carrion and insects or even sick and dieing animals.

Even without a mass extinction there are plenty of species opting for less intelligence.

Carnivores can also go towards herbivorous lifestyle - see giant panda.

Originally Posted by paralith

Carnivores tend to be smarter than herbivores, because hunting down another animal isn't as challenging as finding some grass to chew on.

I think diet may have a role here, with regards brain size proportions.

Originally Posted by KALSTER

I'd say that in a situation where most of life have been wiped out, alot of opportunities would open up where intellegence is not as vital? An animal that changed to an omnivore, could still keep close to it's herbivore origens, but still be able to take advantage of opportunistic meals like carrion and insects or even sick and dieing animals.

Yes, but for how long? If the landscape becomes stable (from a finite number of generations), then specialists will evolve to better fill the available niches - the omnivore (in more ways than one a non-specialist, I'm assuming) will be out-competed on each individual facet of its existence by different specialists. It might even (the lineage that is) become a specialist itself.

Originally Posted by adamd164

Originally Posted by paralith

Carnivores tend to be smarter than herbivores, because hunting down another animal isn't as challenging as finding some grass to chew on.

I think diet may have a role here, with regards brain size proportions.

I agree. Meat is a much more efficient food source, after all; in fact, the eating of meat probably had a significant contribution towards enabling pre-human hominids to develop larger brain sizes. Bigger brains make better hunters; they probably reinforced each other.

i would only like to add to that: fatty meat.

Lean meat is no good for a power hungry brain.

And fish and nuts.

To come back to the original question asked in the opening post, why do there seem to be spurts in evolution?

It's mainly ecological pressure in my opinion. Major changes in the environment can lead to rapid radiaton of species and filling up of the niches that are empty.

I used to think that for instance the cambrian explosion could have been because of the arrival of the genetic developmental toolkit, but more recent research has shown that this is probably not true. The ancestor of all these animals had already all the elements of this toolkit; the same amount of hox genes, the same set of master control genes etc.

Leaves only one option left. Ecological enrichment.

Little squirmy worms got slightly bigger. bigger led to new niches. New forms appeared. new forms led to new forms. A runaway train.

Only once all the niches had fully development the evolution of form slowed down and a pruning was initiated in later phases of evolutionary time.

All of these answers seem to destroy the enigma of evolution spurts. We can see with dogs the different shapes that can develop in a very short time. The sheer variety of available niches can have a similar effect to human preferential breeding. Bacteria being able to very quickly evolve could help the transition between carnivore/omnivore/herbivore. An evolution gene toolkit could speed things up as well. Are there any unanswered questions?

Originally Posted by KALSTER

All of these answers seem to destroy the enigma of evolution spurts. We can see with dogs the different shapes that can develop in a very short time. The sheer variety of available niches can have a similar effect to human preferential breeding. Bacteria being able to very quickly evolve could help the transition between carnivore/omnivore/herbivore. An evolution gene toolkit could speed things up as well. Are there any unanswered questions?

haha. of COURSE there are unanswered questions. Just because we currently have a general idea of what drove certain diversification events doesn't mean we know all there is to know about it. What specifically caused each lineage to diversify the way it did? Which species took over which niches? What were the environmental conditions they had to adapt to? What genes are involved in the transition between feeding types? There are nearly endless details that are still unknown for many things.

Yeh sure the details are far from being known. I mean creationists and theists in general often use evolution spurts as a reason why a god had to make it happen. These points that have been made on this thread seem pretty straight forward to me as a broad explanation of how it happened. I always thought there was some unexplained aspect to this broad idea like the lack of bridging species. Is there anything missing in the larger picture?

Originally Posted by KALSTER

All of these answers seem to destroy the enigma of evolution spurts. We can see with dogs the different shapes that can develop in a very short time. The sheer variety of available niches can have a similar effect to human preferential breeding. Bacteria being able to very quickly evolve could help the transition between carnivore/omnivore/herbivore. An evolution gene toolkit could speed things up as well. Are there any unanswered questions?

We have only found an explanation for evolutionary spurts in the last 20 years. This is when the findings in the field that would later be name evo-devo gave us radical insights into the process of creating form.

Before that a authority figure (can't remember the name) said for instance that it was pointless to look for homologous genes between distant species due to the evolutionary distance between them. That was when we still thought that humans had 100,000 genes.

What a shock it was to learn that all animals basically have the same set of genes. We think it is normal now, but it was a revolution in biology.

The mouse only has a few different genes from humans. Chimps the same basically.

The genes themselves are not qualitatively different. Transplant a gene from mouse to drosophila and it works just fine.

And then we discovered why. Combinatorial control. The genes themselves do not explain the difference in form between mouse and man. It is the regulation of the genes. A regulation that is flexible and cumulative.

And then we discovered the modularity of the developmental toolkit. How can new form or innovation be created? By creating something new? No. By modifying something old. And evo-devo explained how.

That said. We only know examples. We do not know how these processes work exactly, and how they work in different systems.

For instance you can ask if the stripes on the zebra are white on a black background or black on a white background. We can speculated based on the new theories of evo-devo what the correct answer is, but nobody has ever researched the topic.