Another stupid question from Raz!

[Razgovory]

I have an evolutionary biology question.  Anyone can answer.  I bet Viking will know and tell me I'm stupid at the same time, so it's a twofer.  Why do some groups of organisms seem to speciate more then others?  Take for example and ants and hominids.  In the Cretaceous period the ancestors of modern ants looked like... ants.  We can't tell how these animals behaved, but physically they seemed a lot like modern ants.  Our ancestors at the time looked like squirrels.  The changes between us and our squirrely ancestors is quite dramatic.  The changes between dinosaur age ant and modern ant aren't.  Why?  Did they just find an optimal body plan, or are ant genetics just lazy?

[Eddie Teach]

God was satisfied with the design of ants.

[MadImmortalMan]

You're still kinda squirrelly.   


Ants do seem to be a very efficient design for a creature if you think about it. There is also the one queen per thousands thing, which may mean less genetic exchange happening. But I don't know that much about ant cross-colony genetic migration.

[alfred russel]

There is also something to the fact that you are comparing large organisms (hominids) and much smaller ones (ants). Large organisms tend to go extinct during mass extinction events or other more local disruptions. That leaves the niches they filled unoccupied, and an opportunity for a new type of large organism to evolve into that niche.

[Ideologue]

Number of contemporary ant species: 14,000+

Number of contemporary hominid species.  7

[Razgovory]

Ants are only one example.  Another would be a Coelacanth, which the modern species so resembled the ancient one that it is called a "Living fossil".  There are plenty of other examples like crocodiles.  On the other hand mammals have changed quite a bit.  Humans are but one example, but think of vast differences between the ancestors of whales who evolved from small carnivorous animals that looked like something like a wolverine.

[Darth Wagtaros]

Once something works there is no need to change it. 

[alfred russel]

Ants are only one example.  Another would be a Coelacanth, which the modern species so resembled the ancient one that it is called a "Living fossil".  There are plenty of other examples like crocodiles.  On the other hand mammals have changed quite a bit.  Humans are but one example, but think of vast differences between the ancestors of whales who evolved from small carnivorous animals that looked like something like a wolverine.

I think you are changing the nature of the question, or at least how I would have interpreted it from the comparison between humans (a large land based animal) and ants (a small land based animal).

The coelacanth is a fish, and fish species tend to be more resistant to extinction. I could point out that it is only considered a living fossil because it was once a quite common body form and is now exceedingly rare, but there are other aquatic animals that you could use as an example too.

Crocodilians are an interesting example. They have a body form that appears to have evolved multiple times -- I believe including in mammals. The larger crocodilians went extinct in the same event as the dinosaurs, so maybe this is a situation that the crocodilians that are similar to the large ones today actually died out, and were re-evolved from their cousins that survived? I don't know.

[Razgovory]

I had only used humans and ants as examples as they both infest my house.  I was noting that humans are radically different in morphology then dino-age ancestors while ants really aren't.  Hell, humans are radically different then their ancestors 5 million years ago.  Further examples could be crocodiles which look like crocodiles from 100 million years ago and whales that don't look anything like their ancestors from that time period. 

I suspect some of it is do to mass extinctions. For instance when the Permian era ended Dinosaurs took on all sorts of forms.  When the Cretaceous period came to a close mammals speciated into a whole bunch of forms ranging from flying animals like bats to aquatic animals like whales.  Still it doesn't explain why some animals seem to be "In a rut".  I use that figuratively.  Ants are of course some of the most successful animals on the planet. They just seem so unchanging compared to other animals.

[Ideologue]

Ok, I think I get your idea.

First, I think it might be a mistake (I honestly don't know) whether ants 60mya were basically identical to ants today.  I suspect they are very different from their descendants.  But if they aren't--and in terms of morphology, maybe they aren't--it's because they occupied a niche and that niche was never destabilized.

This is why I think they probably aren't identical, but it's feasible.

If humans were incapable of industrialization (for whatever reason, either by being slightly dumber or the Earth itself being poorer) there's a slim possibility that we'd have remained more or less unchanged for the next 60my too due to our easy domination of our ecological niche.  As it stands, we'll almost certainly have radically changed ourselves by that point, of course.  But superorganisms are pretty good at surviving, and we have a lot in common with ants.

Second, I think you may be overstating the difference in morphologies between a human and a lemur or utahraptor or whatever due to your natural anthropic bias.  Ant morphology is that of a six-legged animal with an exoskeleton, and appears relatively constant... well, to an intelligent ant, I imagine so would the evolution of the fleshbound quadrupedal giants.

[Viking]

Without calling you stupid, because this is actually a good question. Ants are radically different from other ants. They just all look the same to us. Remember rats (the third species probably living in your house) and humans both have all the same bones and organs in all the same places, they are just slight variations of each other. The same applies to ants. You are underestimating the variation among ants. To match ants in variation we'd have to group ourselves, not as humans, apes, primatesor even mammals but tretrapods (animals with four limbs, yes that means all birds, reptiles, amphibians and mammals).

Another thing, just because you might look similar that doesn't mean that you are genetically similar. Often the big differences are caused by small genentic mutations.

[Syt]

Wiki says: "More than 12,500 of an estimated total of 22,000 species have been classified."

Which is a lot more than I would have expected, TBH.

[Razgovory]

Without calling you stupid, because this is actually a good question. Ants are radically different from other ants. They just all look the same to us. Remember rats (the third species probably living in your house) and humans both have all the same bones and organs in all the same places, they are just slight variations of each other. The same applies to ants. You are underestimating the variation among ants. To match ants in variation we'd have to group ourselves, not as humans, apes, primatesor even mammals but tretrapods (animals with four limbs, yes that means all birds, reptiles, amphibians and mammals).

Another thing, just because you might look similar that doesn't mean that you are genetically similar. Often the big differences are caused by small genentic mutations.

I don't think ants and tetrapods are good for comparison.  Arthropods and tetrapods may be.  I understand that there many types of ants some quite different from each other, however these variants are not nearly as great as those between man and squirrel.  Or wolverine and whale.  There are radical differences between man and other apes and between different whales but if you were to look at their ancestors prior to the KT boundry you wouldn't immediately be able to say, this squirrel is a hominid or this racoons looking animal is a whale.  When we look at ants caught in amber we can immediately identify them as ants.  There are no ants that have evolved flippers and moved into the oceans or have started to walk upright and use fire and cell phones.

But perhaps using ants was a poor choice.  There are plenty of other animals that are "living fossils", creatures whose morphology has remained static for millions of years.  I can't speak for the genetics of the animals.  I don't know how to read that sort of thing.

[alfred russel]

I had only used humans and ants as examples as they both infest my house.  I was noting that humans are radically different in morphology then dino-age ancestors while ants really aren't.  Hell, humans are radically different then their ancestors 5 million years ago.  Further examples could be crocodiles which look like crocodiles from 100 million years ago and whales that don't look anything like their ancestors from that time period. 

I suspect some of it is do to mass extinctions. For instance when the Permian era ended Dinosaurs took on all sorts of forms.  When the Cretaceous period came to a close mammals speciated into a whole bunch of forms ranging from flying animals like bats to aquatic animals like whales.  Still it doesn't explain why some animals seem to be "In a rut".  I use that figuratively.  Ants are of course some of the most successful animals on the planet. They just seem so unchanging compared to other animals.

Raz, I'd point out a few things...first I'd emphasize that you are discounting too quickly the difference between large and small land animals. There are a long list of small animals (like ants) that have similar looking animal ancestors that haven't seemed to change much through the ages.

But try naming the large ones. You did come up with crocodilians. But I'd question that. First, the order evolved just 83m years ago per wiki (http://en.wikipedia.org/wiki/Crocodilia), so their 100m year date you mentioned is probably inaccurate. Second, the larger ones died off with the dinosaurs, so it is possible that the similarities between modern and ancient crocodilians is due to convergent evolution rather than direct ancestory. It is interesting that you brought up whales--I was indirectly alluding to it earlier. The common ancestor of whales was a mammal that had the appearance of a crocodile (http://en.wikipedia.org/wiki/Ambulocetus_natans). I believe there earlier version of the crocodile body type before the crocodilians--it seems to simply be a stable body type that has evolved multiple times.

In any event, crocodilians may be the exception rather than the rule.

[Malthus]

Ants may be on the cusp of a major new evolutionary pressure - with one species (the Argentine Ant) apparently taking over vast swaths of territory and eliminating all competition.

Actually, it is even more bizzare than that - as these Argentine ants appear to be, not simply one species, but in some senses a single individual hive - genetically identical, even when on different continents.

This change is caused by humans moving ant colonies around accidentally.