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A question I've raised on Twitter I shall raise here as well--Australia has giant crocodiles, the most venomous snakes on Earth, spiders that can kill you, and even giant stinging trees. Why is evolution so nasty in Australia?
thren toejam's profile photoEmily Banyard's profile photoMatthew Waldman's profile photoTony Sidaway's profile photo
Speculation: Evolution operates by chance and through environment. Australia might have one of the roughest terrains in the world and hence the animals that existed were to be tough to survive. Survival and competition among these tough species require additional defenses such as venom, poison etc. Also, the initial draw of animals that inhabited the land might by chance be of the toughest kind.

Also, Australia is repeatedly subjected to many more violent vagaries of nature such as forest/bush fires, droughts and floods.
The only obvious gap in the environment in Australia is lack of Placental Mammals but I fail to find any correlation there. Even their seas host incredibly nasty (and bizarre) specimens, like a carnivorous Sea Squirt ( )
And yet there are so few fatalities here. Makes me think they have to work harder at being nasty just to have any credibility at all.

Why does North America have so many mammals that are predators of humans?
I guess nastyness is a good thing when you want to survive in a nasty environment. Life is hard, especially in Australia.
Wombats and Koala's are nice and friendly though.
50k people die in Europe each year due to antibiotic resistance superbugs, how many Australians die as a result of giant crocodile attacks?
At least for sealife other countries in that part of the world have much the same fauna. The list of dangerous sealife is fairly impressive in Okinawa as well, and include many of the usual suspects in Australia. But it's not something people tend to bring up as a conversation topic here.

Which leads me to ask to what degree Australia really has more dangerous wildlife than other countries in southwest Asia? Or is it mostly a matter of perception?
Well, once there's one incredibly deadly species, maybe the others have to become deadlier to combat it. Sort of an evolutionary arms race. When the jellyfish are badasses the fish have to be badasses, when the fish are badasses the birds have to be badasses, and so on up to Crocodile Dundee.
Like Jan, I wonder how much of it just exoticism.

Jeff Simmermon once told a beautiful story at The Moth about working as an apprentice to a trapper. He was amazed at how calmly the trapper dealt with all of the dangerous/poisonous/etc. animals. Then, one night over dinner it came out that Jeff had once seen a bear. The trapper was stunned that Jeff didn't soil himself at the sight of such a ferocious creature.
Sounds like a theoretical problem for complex adaptive systems modeling ;-). Since Australia's distinctive terrestrial native flora and fauna are clearly related to island segregation effects, intuitively isolation must have something to do with it (if, as people point out, this actually is a real distinction -- how exactly, Carl, do you quantify "nastiness" in an ecosystem? How about the microbial ecology?).
Is it really all that "nasty" or does it just appear nasty from a human perspective because we (placental mammals) didn't evolve along side the native flora and fauna?
Maybe Evolution was trying to compensate desperately for the cuteness of Koala bears and the platypus (platypi?)
Down under, even cuteness is laced with venom. Every male platypus has a set of ankle spurs that produce a venomous cocktail.
I wonder if the lack of large mammalian predators leads to an increase in reptilian predators?
Australia is sparsely populated. In areas with more dense human populations, we've eradicated the nastiest beasts.
My assessment: not nastier, just a bit different - mostly due to it being an island.
I remember considering that problem once, and I recalled some speculations from Robert Bakker's Dinosaur Heresies and elsewhere. He considered why some Indonesian islands have the Komodo Dragon as their top predator -- why a cold-blooded and not a warm-blooded one like a tiger? Warm-blooded ones would have to eat more prey flesh per unit body weight to survive, and there'd be fewer individual ones. They'd thus be more vulnerable to genetic drift and droughts and the like.

Australia, though a continent, is actually very island-like, because much of it is desert and much of the rest semidesert. Thus, it could support much fewer warm-blooded predators than mainland areas, allowing cold-blooded ones to flourish.

Low density of prey may also explain the strong venom of some Australian snakes -- it would be a way of keeping energy consumption down, since the snake would have to move less.
I don't think evolution is that nasty in Australia. It's a limited environment with a limited gene pool. Their native wildlife is getting absolutely destroyed by imported mammals such as mice, rats, rabbits, etc. So while the poisons and such might be a specialty adaptation that's good for defending Australian native life against other Australian native life, it's still not very effective as a defense against the world's wildlife.
Ed Yong
Dylan Moran on Australia: "It’s about three quarters of a mile away from the surface of the sun. I’ve seen insects walking around with knee pads. It’s not supposed to be inhabited, and when they’re not…frying themselves outside, they all fling themselves into the sea, which is inhabited almost exclusively by things designed to kill you. Sharks, jelly fish, swimming knives, everything."
I think +Dave Bridges offered the crucial clue. Snakes have a larger share of the predator niche in Australia than on other continents, whether this is due to the climate or some other reason. This makes it more important for Australian marsupials to develop resistance against venom, the evolutionary pressure favoring venom resistance is stronger in Australia. This in turn makes for a stronger evolutionary pressure on the snakes to become nastier. I have a vague thought that I read something like this before but now I can't find it :(
Lucas, we have possums (phalangaroids) in Australia - not to be confused with opossums (didelphids) which belong in an entirely different order of marsupial. Not to mention that study was conducted on animals from an entirely different continent as well... But on your point, yes of course evolutionary arms race goes both ways
Thanks for your correction Tommy! I've edited my comment accordingly.
Most of these imported species are herbivores, and the carnivores are relatively small. Cats are typically 5 kg, and foxes not much more than that. The dingo, a feral dog that is now Australia's largest warm-blooded predator, goes up to 20 kg, and the now-extinct thylacine went up to 30 kg.

Australia's warm-blooded predators are thus very wimpy by the standards of the continents, where lions and tigers average out at about 150 - 200 kg, and bears get even bigger.
One thing to keep in mind is that Australia's current ecosystem, since about 50,000 years ago, has gone through major change, with the loss of a whole host of megafauna, including most of the major predators. This includes marsupial lions, marsupial tigers, and a large venomous dragon that the Komodo dragon is probably a miniaturised island version of. It's not impossible that the various poisonous animals were competing/defending themselves against a now extinct animal.

Another thing to remember is that Australia is a continent, with a huge variety of ecosystems, from alpine ranges to tropical swamps to desert. I suspect there isn't one simple answer to the question Carl's asked, but that different animals might be dangerous for different reasons in different habitats. 
The marsupial lion went up to 100 kg, so it's at the low range of placental lions and tigers. The marsupial tiger = thylacine or marsupial wolf. Megalania was a giant lizard, and was almost certainly cold-blooded.

But if one wants to judge by extinct Pleistocene predators, North America and Eurasia had lots of them. Lions, bears, sabertooth felines, ... without any predatory giant lizards.
Geology has the answer. Evolution requires isolation of populations over vast stretches of time. Australia's been an island unto itself for the last 80 million years. Very little intermingling of land-bound populations for that stretch of time will make for some nasty evolution.
I don't know, but I'll toss out a guess, Carl. Why is Silicon Valley a hub of tech startups (Intel, Google) while Detroit became a hub for cars (Ford, GM), and Las Vegas a hub for casinos and magicians? I think once an area gets started in a particular direction, by random chance (and in biology, all evolution starts with random chance mutations), competition can drive it further in that direction. Australia has gone very far in the "poison" direction. I once saw a list of the world's top 10 most poisonous snakes, and all*10 were from Australia! Other parts of the world went in other directions. Africa, for example, went in the direction of primates with big brains :) It's just as fair to ask, why did Africa go in that direction, isn't it? The thing that amazes me about Australia, though, is how many different types of life are poisonous -- not just reptiles, say, or insects, or sea life, but practically everything. It's astonishing.
Australia is full of deserts, so it's a long way from one meal to the next. So the predators that tend to thrive are the ones that can guarantee a kill on the largest rare meal that happens to blunder along. Venom is a very good force muliplier.
Really interesting discussion here. It seems that the hypotheses proposed fall out into about four categories (or some combination):

>1) Environmental something particular about the continent itself, either the hostile conditions (arid, disaster prone), or its insularity.
>2) Biological either owing the the unique ecosystem structure (dominance of reptilian predators) or driven by arms races (snake vs. marsupial).
>3) Coincidental Australia just happens to be the center of diversity for a few very dangerous clades.
>4) Illusory It's not actually more nasty than any pace else (the core of the counter argument in the Cecil Adams post that was linked to).

For the marine realm I kind of favor a combination of 2+3. The Indo Pacific is a major so it is just statistically more likely to have the most deadly representative of any given group (and it does: cone snails, blue ringed octopus, box jellies, stone fish). Plus high-biodiversity might tend to amplify predator prey arms-races.

The terrestrial pattern seems harder to explain. I like Martin's suggestion, certainly the Australian elapid radiation helps to explain where so many of the "mostest deadliest" snake species live there (and so many of the others are in nearby SE or South Asia). I also wonder if the low basal metabolic rate of marsupials makes them harder to kill with venom than placentals? There are a few papers that back that up. The venom as response to prey scarcity in arid environments is an interesting idea too - but many of the deadly arachnids and snakes live in the comparatively humid coastal areas, or the tropical Northeast. I too, am skeptical that it is simply an "insular nastiness" effect.
Re: "insular nastiness"

Isolation is often cited as the reason for Hawaii's relatively benign flora and fauna. Interesting that there may be some insularity threshold such that somewhat restricted gene flow results in evolution of "nasty" food webs and virtually no gene flow results in the evolution of depauperate, mild ecosystems.

We see nastiness evolve in biological invasions as the result of multiple introductions of species to new areas, sometimes from different origin populations. The new area is isolated, but not so isolated that novel genotypes won't be generated by the reunion of partially diverged populations. This gives the invading populations a wildly diverse gene pool for selection to act on and can result in some incredible adaptive "leaps."
its not so much nature thats nasty, its your perspective of things....
Look at it from a naturaul selective point of view,,,,,your 4 year old survives the giant crocs, spiders, snakes etc.... it improves our bloodstock.. the 4 year old... well.....

thats why Aussies are tough... we are a product of our enviroment.


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That's rubbish. The attrition rate from venomous animals and other unique environmental factors simply isn't high enough and Australia hasn't been heavily populated for long enough for natural selection to have an effect at the level of the population, or even local populations for that matter.
@ Tony, interesting.... my people been here a bit longer than a couple of hundred years.
So I will disagree with you on it having an effect on "the local population" , the local population has been here and learnt to live with our enviroment. 60,000 years long or so they say.
My original post was tounge in cheek. yes we have some nasty animals, but, if you are aware of your sourroundings and not have to be very very unlucky to be hurt by our wildlife.
Yes they can be dangerous, but mostly its the people not the animals that put themselves in danger.

I stand by the argument that we are a product of our enviroment.
Its all a ploy to turn people off - we want to keep paradise clean ;). And in over 20 years, with snakes and spiders on my doorstep and sharks in the ocean I swan - I never got attacked by anything!
quite simply, australia has seen millions of years of long droughts which means that competition for calories is even steeper than other continents, so many predators developed strategies to ensure that prey can not get away as every meal is precious. even marsupial reproductive strategies are perfectly tuned for surviving long droughts...
A good evolutionary reason for developing powerful venom is to ensure a kill where food is rare. Another reason is survival. The two work together. A snake or spider that can deliver a big enough dose of a powerful venom to kill quickly has a better chance of surviving a rare encounter with a food animal that may well have good defences, and it also stands a better chance of having access to a large meal. It's no use injecting poison if the victim will wander out of range before it dies.
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