Why haven't animals adapted to highways by now?

Factual Questions
21

There are many ways by which an animal might adapt to roads, not all of which would require intelligence. A species might, for instance, develop a genetic predisposition against the smell of asphalt, or of gasoline fumes. Any individuals with this gene would tend to stay away from roads entirely, and hence (if roadkill is a significant cause of mortality, and there isn’t a corresponding benefit to crossing roads) be more successful. Or an animal might evolve an armor or other physiological changes of a sort sufficient to protect against being run over (which would also incidentally protect against some types of predators). Or a species might develop more towards a R-selected reproductive strategy, such that those individuals which are killed by cars don’t matter much.

In response to some other posts, evolutionary “learning” does not require any particular individuals to learn, nor does it require that any individual survive encountering the threat. Let us suppose that there is a species of animal, some of which have a tendancy to engage in a dangerous behaviour, and some of which do not. Let us further suppose that this tendancy is in some way heritable. Why they don’t engage in the behaviour doesn’t matter: Maybe they’re smart enough to know it’s dangerous, or maybe they just don’t like the smell of asphalt, for no particular reason. Likewise, how the behaviour is inherited is also irrelevant: It might be genetic, or it might be Mama Animal communicating somehow to Baby Animals to do or not do something.

Now, let’s look at what happens in that population of animals. Some of them engage in the dangerous behaviour, and get killed. Most of the ones who get killed were the ones with the heritable tendancy to do so. All other things being equal, this means that the ones with that tendancy will tend to have fewer offspring, and since this tendancy is to at least some degree heritable, that means that fewer of the next generation will have that dangerous tendancy. So over time, you’d expect to eventually see that dangerous tendancy disappear, and all of the animals would avoid the dangerous activity, whatever it is, even without any individual learning anything.

22

A bit nit-picking. Obviously some degree of evolution happens every second. But the kind of evolution we’re talking about in this thread - enough naturally occurring mutation and selection to cause a noticable change in a marginal behavior of a mammalian species as a whole - requires a lot more than a century to happen.

23

Colibri nailed it. And Chronos showed how it could happen, if highway deaths was a serious factor in the natural selection of woodland critters.

24

I wonder if that coyote (post #7) would be able to teach her pups to look left and right when
crossing streets. While the requisite intelligence would be inheritable the actual information
being conveyed would be “cultural” (for lack of a better word), correct?

25

[QUOTE=Chronos]
Likewise, how the behaviour is inherited is also irrelevant: It might be genetic, or it might be Mama Animal communicating somehow to Baby Animals to do or not do something.
[/QUOTE]

[QUOTE=John DiFool]
I wonder if that coyote (post #7) would be able to teach her pups to look left and right when
crossing streets. While the requisite intelligence would be inheritable the actual information
being conveyed would be “cultural” (for lack of a better word), correct?
[/QUOTE]

Excellent post by **Chronos. ** However, just to clarify in response to John’s post, the kind of behavior that Chronos is describing - the transmission of learned behavior across generations, or to other members of a species - isn’t properly referred to as “inherited” but better described as culture.

26

I think it also depends on the neural wiring/survival mechanism of the particular animal.

For instance, in Mississippi, I’d see the occasional rabbit and squirrel flattened out on the road, but way many more opossums and armadillos. Rabbits and squirrels dodge around, but generaly can continue on a more or less straight trajectory, and have large eyes, so some judgement of what to do in a situation with an oncoming vehicle, at close range.

Opossums and Armadillos: not adapted for that sort of movement at all. Small eyes, not suited to extreme movement. An opossums adaptation to extreme stress is to freeze, open it’s mouth and look like a badass, but, really, they’d rather avoid conflict, so then “Play Dead”. This doesn’t work with oncoming cars. They just freeze up by nature. Their forte is excellent hearing, but that doesn’t do a whole lot when crossing the oad.

Armadillos are wired, when stressed, to jump straight up and use the “Holy WTF!!!” mode of surprize for a pedator. Again, it doesn’t work well for an oncoming car or semi- truck. I found many that died from damage to the top part of their body, indicating delayed response and popping up, wiped out on the undercarriage of a large truck. Not likely that could be 'Unlearned".

27

Hmm…well it occurses to me maybe while we all see the dead deer in the middle of of the road maybe what we say, maybe the famility that didin’t take the risk a starved to death when their land was bifircated were the ones who didn’t take the wise choice. `Just thinking.

28

[QUOTE=John DiFool]
Why haven’t animals adapted to highways by now?
[/QUOTE]

How do we know some species haven’t? It wouldn’t require a complete cessation of roadkill, just a reduction. I’ve often wondered if there has been a reduction over the last 50 years for smaller creatures that breed quicker.

29

[QUOTE=Shalmanese]
Only if the behavior is genetic, not learned. Otherwise the behavior won’t be passed onto the next generation unless it can be taught.
[/QUOTE]

Right, but intelligence that led to it being learned might be genetic. We’re not talking about evolving dogs that are born with a fear of roads. We’re talking about evolving dogs that are smart enough to figure out how a road works and figure out what it has to do to stay alive.

30

[QUOTE=Mangetout]
But any distinctive threat can concievably elicit a different response - plenty of animals have different escape strategies for different kinds of predator attack (i.e. if threatened by hawks-duck & cover, snakes-run away fast, dogs-climb a tree) a moving vehicle is just another kind of threat, and possibly one that can be distinguished from the others enough to elicit a distinct response.
[/QUOTE]

True, but selection for such a specific thing would be more complex and might take longer to occur.

31

[QUOTE=elelle]
Armadillos are wired, when stressed, to jump straight up and use the “Holy WTF!!!” mode of surprize for a pedator. Again, it doesn’t work well for an oncoming car or semi- truck.
[/QUOTE]

True, but their vulnerability on our roadways doesn’t seem to be slowing the steady expansion of the armadillo empire:

So I don’t know how much selection pressure the roads are exerting on armadillos.

32

[QUOTE=spoke-]
True, but their vulnerability on our roadways doesn’t seem to be slowing the steady expansion of the armadillo empire:
So I don’t know how much selection pressure the roads are exerting on armadillos.
[/QUOTE]

This is kewl! Will the armadillos expand into new England? We have LOTs of coyotes here, now.

33

[QUOTE=ralph124c]
This is kewl! Will the armadillos expand into new England? We have LOTs of coyotes here, now.
[/QUOTE]

The expansion of the armadillo range is probably limited by winter temperatures, since they don’t have dense fur or great temperature control. How far north they get eventually may depend on climate change.

34

I’m still waiiting for love bugs to be affected by highways. I don’t know about you guys, but I’m probably responsible for several million deaths.

No one has mentioned it, but their may in fact be less roadkill in your areas because of development. I live in the city now, and see mostly dogs, cats and squirrels. But when I lived in the country, the variety of roadkill was much greater.

If you have ever seen how much damage a deer does to a car (I can only imagine a moose) it hasn’t selected us from having cars in deer/moose prone areas. Then again, the cars I’ve seen didn’t live long enough to reproduce and weren’t of a high enough brain functioning to pass that trait on.

35

[QUOTE=Little Nemo]
A bit nit-picking. Obviously some degree of evolution happens every second. But the kind of evolution we’re talking about in this thread - enough naturally occurring mutation and selection to cause a noticable change in a marginal behavior of a mammalian species as a whole - requires a lot more than a century to happen.
[/QUOTE]

Not nit-picking at all. Rate of genetic drift leading to phylogenetic differences that become pervasive in a population varies based on a whole host of factors, including size of population, lifespan and reproductive age, extent of selection pressure, genetic diversity within the population, etc. But for small, reproductively isolated populations with relatively short lifespans and low reproductive ages, it can happen far more quickly than most people expect. Jonathan Weiner’s The Beak of the Finch, while dealing with avian and not mammalian species, makes this point pretty conclusively.

That being said, to address the OP, it’s not enough for some adaptation to be advantageous in order for it to be selected for – it has to be present in some subset of individuals in a population. Not every potentially advantageous adaptation for a given species can be expected to occur through random genetic variation. And you can only get there through variation of the genetic material that’s already there – not to mention that such variation has to be of a nature that’s compatible with the rest of the species’ genome.

The greater the degree of variation in a population, the greater the likelihood of an advantageous mutation occurring, but the larger the population, the harder it will be for any one variation to become prevalent. The faster the population turns over (i.e. the shorter the average lifespan, the larger the size of litters, etc.), the faster such changes can take root and become dominant.

In short, while I agree that the answer is at least in part that there hasn’t been enough time, it’s as much that until recently there were no analogous natural dangers to most species, so that evolution is having to “start from scratch”, so to speak, in selecting potentially useful variations, instead of being able to build on thousands or millions of years of adaptation to similar threats.

36

[QUOTE=Mangetout]
I don’t see why this would be such a huge problem - not all animals react in this way; if a mutation occurs that happens to modify instinct in such a way that they tend to run in a different direction, it will be positively selected by the increased survival rate around roads - it’s that simple. The reason it hasn’t happened much, if at all, is that cars have only been around a little while, in evolutionary terms.
[/QUOTE]

Well, when I said it’ll never happen, I was right. Given the constraints of the real world we live in.

First, you need *a * mutation. That in itself will take a while.

Then, said mutation needs to be *beneficial * (to this specific situation). Again, gonna take a while.

Then, that animal has a lot of breeding to do (well, him and his offspring, which may or may not have the gene in dominant form), enough to completely replace the older “unenhanced” generation. Again with the time thing.

Then I said that by that time the situation will have changed - (maybe we’ll have flying cars by then - lookout birdies!!!).

So, it’ll never happen. Man, I sure do come across as inflammatory don’t I? I really gotta work on that. :stuck_out_tongue:

37

[QUOTE=echo6160]
First, you need *a * mutation. That in itself will take a while.
[/QUOTE]

This is a common misconception. In fact, a lot of evolution takes place just by acting on existing genetic variation in a population. And novel traits can arise just by interactions between presently rare alleles of different genes.

A lot of species probably have the basic wherewithal to be able to avoid becoming roadkill if they were strongly selected for that. They have the perceptual ability to be able to distinguish a road from other kinds of hazards, and could potentially recognize vehicles as a “predator” even if it were a long way away. The reason they have not done so is most likely that the selective pressure from roadkill is just not strong enough compared to other factors for anything to have resulted in the short time this particular hazard has been around.

38

Why haven’t animals adapted to predators?
Because cheetahs and owls, like cars, have gotten faster and quieter.
Q. Why did the chicken cross the road.
A. So show the [armadillo:possum] it could be done.

39

[QUOTE=Chronos]
There are many ways by which an animal might adapt to roads, not all of which would require intelligence. A species might, for instance, develop a genetic predisposition against the smell of asphalt, or of gasoline fumes. Any individuals with this gene would tend to stay away from roads entirely, and hence (if roadkill is a significant cause of mortality, and there isn’t a corresponding benefit to crossing roads) be more successful. Or an animal might evolve an armor or other physiological changes of a sort sufficient to protect against being run over (which would also incidentally protect against some types of predators). Or a species might develop more towards a R-selected reproductive strategy, such that those individuals which are killed by cars don’t matter much.
[/quote]

One can postulate ad infinitum regarding potential ways in which organism can adapt to this or that. That does not make any of them possible or even likely. Natural selection acts on variations, selecting for those variations which yield an advantage to an individual, and selecting against those which yield a disadvantage.

Avoiding roadways altogether for an established species is likely to simply not happen. The roadway was plonked down in their territory, which is the reason they make attempts to cross said road in the first place. It’s an artificial, albeit not insurmountable, barrier. Depending on the size of the creature and its territorial needs (and the actual danger presented by the road), avoiding roads may restrict the available territory to an unreasonable amount (and, as often as not, reduction of available territory is the first step towards extinction). For the most part, animals which are struck are struck as a result of bad timing on their part, not because the road exists at all.

Armor is unlikely to evolve specifically for the purpose of safe road-crossing. Armadillos already have armor, and it doesn’t help them much against a 2000-lb vehicle. Again, NS works on variations. A slight variation in the amount of armor is not likely to help against several thousand pounds of steel. Such variations, in the context of road safety, would very likely be simply neutral, as there’s no practical benefit for slight changes. Not only that, but increased armor usually means increased weight, which also means decreased speed. When playing the real-world equivalent of Frogger, speed is likely to be more important than armor.

Switching reproductive strategies is highly unlikley, unless the roadway represents a significant effect on the mortality of a population. Which is itself unlikely to be the case.

All of which is largely moot, of course, as there hasn’t been enough time, nor, as has been pointed out, do roads present a significant selective factor for most species. Not to mention the fact that not every motorist will plow willy-nilly into any crossing critters. We have done significantly more to adapt (in a cultural sense) to animal crossings than animals have adapted to roadways, which further decreases the selective pressures involved.