Thread: Urban Evolution

From the CBC, a story of the pace of evolution. Millions of years required? Maybe not in some cases. I think the animals mentioned in the article illustrate the fact that subtle variations and mutations are taking place all the time. I think it's a testament to the wonders of evolution. Why, how.... does a fish adapt to PCB's? It certainly wasn't that way originally. Fascinating stuff IMHO.

Edit: I think I may have erred when I said the fish wasn't that way originally. What I mean is, there had to have been some fish resistant to PCB's when the toxin was introduced would there not? Or would the introduction of PCB's to the fish' environment spur the changes?

Noticable genetic changes within 5 to 10 generations time.
That is shockingly fast.

Noticable genetic changes within 5 to 10 generations time.
That is shockingly fast.

In some cases I think it might just be selection by elimination.

University of Tulsa ecologist Charles Brown says he was surprised it took just 30 years for the cliff swallows in his study to evolve shorter wings that help them avoid traffic.

I don't think that's evolution as people commonly understand it, i.e. gradual changes. I think it's more attributable to simply killing off the portion of that particular group with the less manoeuvrable wings. I'd presume that other populations of the same bird still have the full variety of wing spans that the bridge group started out with.

Originally Posted by adelady

University of Tulsa ecologist Charles Brown says he was surprised it took just 30 years for the cliff swallows in his study to evolve shorter wings that help them avoid traffic.

I don't think that's evolution as people commonly understand it, i.e. gradual changes. I think it's more attributable to simply killing off the portion of that particular group with the less manoeuvrable wings. I'd presume that other populations of the same bird still have the full variety of wing spans that the bridge group started out with.

Except in this case, the killer/predator, doesn't really improve their hunting techniques/skills to match that of the birds. Traffic is traffic, doesn't purposely seek out the birds to kill them.

Originally Posted by adelady

Noticeable genetic changes within 5 to 10 generations time.
That is shockingly fast.

In some cases I think it might just be selection by elimination.

University of Tulsa ecologist Charles Brown says he was surprised it took just 30 years for the cliff swallows in his study to evolve shorter wings that help them avoid traffic.

I don't think that's evolution as people commonly understand it, i.e. gradual changes. I think it's more attributable to simply killing off the portion of that particular group with the less maneuverable wings. I'd presume that other populations of the same bird still have the full variety of wing spans that the bridge group started out with.

I believe you are on the right track here. But it's not just dying out that causes a species to evolve, but mate selection can play a big part also. You can't have evolution without new generations and if you don't mate, then your the last of your line. The more generations you have in a specific time frame the faster that species will evolve. So the fastest evolving life forms are the numerous small life forms at the bottom of the food chain, which is as it should be. The bottom of the food chain needs to survive in order for the higher life forms to continue surviving. As the life forms get larger and more complex with longer lifespans as in the case of humans our generations average about 20 years. So we evolve rather slowly compared to the life forms we depend on for survival.

Even then most of our adaptations don't change our physical appearance when they do happen. People that don't die from a disease have a better chance of passing that resistance on to their offspring. Back in the time the plague killed about half the worlds population, the survivors were the ones that were more resistant to that disease. After that the plague still cropped up, but never killed that same high percentage of the population again. Mainly because more resistance genes existed and were passed on to new generations of humans.

Originally Posted by adelady

University of Tulsa ecologist Charles Brown says he was surprised it took just 30 years for the cliff swallows in his study to evolve shorter wings that help them avoid traffic.

I don't think that's evolution as people commonly understand it, i.e. gradual changes. I think it's more attributable to simply killing off the portion of that particular group with the less manoeuvrable wings. I'd presume that other populations of the same bird still have the full variety of wing spans that the bridge group started out with.

It would seem the population from under the bridges are not mingling with the other populations though. It looks to me almost like the start of species differentiation from one part of the population adapting itself into a new environmental niche. This kind of maks me wonder if it will just become a separation on range of habitat or if it will soon be found the shorter winged swallows are no longer able to breed with the longer winged swallows and become a genetically distinct species.

Of course if the traffic went away there would cease to be any selective pressure for the trait and the longer wings would become the dominant trait again, unless the cars are not the only pressure but something else is too.
Maybe the insects the swallows feed on swarm under the street lights and shorter wings make it easier for the birds to catch them there.

As always I am a bit leary of singular causes for events that are complex.

Originally Posted by adelady

I don't think that's evolution as people commonly understand it, i.e. gradual changes. I think it's more attributable to simply killing off the portion of that particular group with the less manoeuvrable wings. I'd presume that other populations of the same bird still have the full variety of wing spans that the bridge group started out with.

But surely, while rather blunt, that is one of the more common paths to rapid evolution. We see it here as well as other well documented examples such as in quick difference of bird beak shapes after a drought, or the altered digitize track with new organs for that lizard near the mediterranean after loosing it's native food source.

Originally Posted by adelady

I think it's more attributable to simply killing off the portion of that particular group with the less manoeuvrable wings.

I think that that, in a nutshell, is natural selection.

I noticed this on Science Daily. Fossilized human feces from 14th century contain antibiotic resistance genes -- ScienceDaily

I assume these genes must have been useful for other things and weren't just waiting around for us to invent antibiotics. Combatting natural antibiotics or toxins?

Why are we more inclined to think evolutionary change takes thousands of years if not more? Changes in physiology and in learned habits are a couple of ways creatures evolve but where in the manual does it say it can't be quick? However, many of these rapid evolution cases deal with having to adapt to living amongst humans, such the term urban. So I was just wondering if in the past, sans humanity, would it have been entirely possible for rapid evolution to take place if, say some other creature suddenly dominated the landscape putting selective pressures on native inhabitants? I can't see how it couldn't have occurred but I've been wrong before.

Originally Posted by zinjanthropos

Why are we more inclined to think evolutionary change takes thousands of years if not more? Changes in physiology and in learned habits are a couple of ways creatures evolve but where in the manual does it say it can't be quick? However, many of these rapid evolution cases deal with having to adapt to living amongst humans, such the term urban. So I was just wondering if in the past, sans humanity, would it have been entirely possible for rapid evolution to take place if, say some other creature suddenly dominated the landscape putting selective pressures on native inhabitants? I can't see how it couldn't have occurred but I've been wrong before.

The life in any given area reaches a stable equilibrium with themselves and the climate. As long as the equilibrium remains fairly stable there will be a minimum of pressure for evolutionary change. After that anything that changes that equilibrium has a lot of potential to cause evolutionary change. This is exemplified when we say an invasive species is introduced into a stable environment, and I don't know any more invasive species than humans. We move into a neighborhood and the creatures that don't adapt go extinct.

imo we greatly underestimate the amplitude of mutations/diversity already present in populations. some humans are born with 6 fingers, if an extiction event wiped out all humans except a tribe in the south pacific where people have 6 fingers, would you say the change for humans to go from 5 to 6 fingers took 1 day or 1000 years? neither views would be an accurate understanding of the process in this example because the label "human" is simplistic(it discribes a wide range of diversity and mutations), humans with totally diffenent T-cell elements have coexisted and mingled for hundreds (if not thousands) of years yet we use the same label and are unable to distinguish these(T-Cell alterates) along with a great many other variations that are not apparent to the eyes (eyes which we use to make abitrary and irrelevant distinction, like so called "white " and "black", but thats another story). my layman opinion at this point in time anyway

Originally Posted by zinjanthropos

Why are we more inclined to think evolutionary change takes thousands of years if not more?

Because usually it does.

Changes in physiology and in learned habits are a couple of ways creatures evolve

Learned habits are not a factor in evolution.

but where in the manual does it say it can't be quick?

It can be! But it usually isn't. It's usually thousands of generations of minor improvements adding up to a big improvement.

Originally Posted by billvon

Originally Posted by zinjanthropos

Why are we more inclined to think evolutionary change takes thousands of years if not more?

Because usually it does.

I'm not sure that's all that well established at all. We can model it either way and have records that support both very rapid as well as what appears to be quite slow.

Originally Posted by Lynx_Fox

Originally Posted by billvon

Originally Posted by zinjanthropos

Why are we more inclined to think evolutionary change takes thousands of years if not more?

Because usually it does.

I'm not sure that's all that well established at all. We can model it either way and have records that support both very rapid as well as what appears to be quite slow.

Could it be that rapidity in itself is an evolutionary advantage?

Learned habits are not a factor in evolution.

At the time I posted I was thinking of the urban raccoon population. They did a study that showed raccoons have figured out how to avoid vehicle traffic simply by using overhead utility wires as their means of crossing the street, something their rural cousins/road kill don't deal with. They didn't evolve any particular physical features to achieve this and their urban populations continue to grow successfully. Also I would count humans in as an animal that successfully adapts without any new physiologically noticeable features.

Originally Posted by DianeG

I noticed this on Science Daily. Fossilized human feces from 14th century contain antibiotic resistance genes -- ScienceDaily

I assume these genes must have been useful for other things and weren't just waiting around for us to invent antibiotics. Combatting natural antibiotics or toxins?

Yes, natural antibiotics are quite common. The weird part isn't that the DNA was there. The weird part is it was in viruses that infect the bacteria in the digestive tract.

I don't understand that part of it and wish the article had explained it a bit more.

Originally Posted by Lynx_Fox

I'm not sure that's all that well established at all. We can model it either way and have records that support both very rapid as well as what appears to be quite slow.

If you are talking about (for example) the punctuated-equilibrium crowd vs the gradualists - I agree; there's a lot of debate. But even the PE crowd would not claim significant change in few generations. "Rapid" in evolutionary terms is generally thousands of years.

If you are talking about (for example) the punctuated-equilibrium crowd vs the gradualists - I agree; there's a lot of debate.

Hmm. Under the impression that there hasn't been that debate for decades, with most biologist recognizing that both can happen depending the severity of selective pressure and range of genetic variability and mutations available to generations of the organism. If for example, some pandemic wiped out 90% of a species in a few generations, the successive generations of survivors will very rapidly evolve to resist or go completely extinct.