In my world, set some time less than 100 years in the future, there have been changes in climate in many places due to global warming. Also, some organisms of extraterrestrial origin got loose and have become endemic in some places. Many of them are pests.

At the same time, it has been discovered that some terrestrial species have evolved very rapidly - more rapidly than classic Darwinian evolution would suggest. It's meant to be a minor unexplained detail, suggesting to the reader that there are a lot of things about this world that simply aren't understood. Maybe there is something epigenetic going on that current science doesn't know about, or maybe the extraterrestrial species caused it in some way.

I'm thinking at some point, someone discovers a new type of bird in the wild which has only appeared within the last 30 or 40 years, is different enough that it's unequivocally a new species but has an evolutionary lineage to existing birds. Or perhaps the new species could be corals or worms.

I want this to be unexpected given our current understanding of evolution, but not contradictory to it. Also, this should not be the result of intentional human activity such as genetic engineering. Is this plausible given what we know today?

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    $\begingroup$ Look into industrial waste lakes, fish and other creatures have been noted to evolve within decades there. $\endgroup$
    – ErikHall
    Commented Mar 16 at 9:54
  • $\begingroup$ Please do not answer in comments. Note that we have had many questions about how to get "evolution" to happen faster, such as worldbuilding.stackexchange.com/questions/186470/… and worldbuilding.stackexchange.com/questions/39264/… - please see whether the answers to these questions and others with the [evolution] tag provide the information you are looking for. $\endgroup$ Commented Mar 16 at 10:19
  • $\begingroup$ "should not be the result of intentional human activity such as genetic engineering" meh, I'd just go with unintended consequences of something, eco terrorists or others release a bunch of transgenic retro viruses that maybe mutate a little to do more than intended including picking up and transfering genetic material from one species to another resulting in a sudden uptick of weird and unexpected 'evolution' $\endgroup$
    – Pelinore
    Commented Mar 16 at 10:50
  • $\begingroup$ popularmechanics.com/science/animals/a45487047/… 16000 year is pretty fast $\endgroup$
    – Pica
    Commented Mar 16 at 10:51
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    $\begingroup$ @JBH added evolution tag $\endgroup$
    – Batperson
    Commented Mar 17 at 23:19

5 Answers 5


Yes, species with fast reproductive cycles, such as small birds, can evolve very fast. Species with slow reproductive cycles, such as elephants or humans, not so much.

  1. The use of the phrase "Darwinian evolution" in a question tagged "science" is unexpected. Charles Darwin was a great writer and a great biologist, but he lived a century and a half ago. The current text-book theory of evolution is the Ernst Mayr and Theodosius Dobzhansky's Modern Synthesis, which integrates Darwin's evolution-by-variation-and-selection with population genetics; and biologists already know that in the near future it will have to be replaced by an even moderner synthesis, which will probably also integrate the progress in evolutionary developmental biology.

    If you insist, you may call the modern theory of evoluion neo-darwinist; but plain "Darwinian" is wrong and a hundred years out of date.

  2. "Is different enough that it's unequivocally a new species" is unequivocally not how species work. If is different enough would be a valid criterion, then chihuahuas, wieners and great danes would be three different species, and they are not.

    Big dog and little dog

    Two clearly different animals, but the same species. Photograph by user [Elf], available on Wikimedia under the Creative Commons Attribution-Share Alike 3.0 Unported license.

  3. Nobody would be quite that much surprised that a new morph or geographic variety of a bird species has been observed. Birds are known to exhibit very fast evolutionary responses to changing life conditions. For example, search for rapid evolution in urban birds. (Link goes to a Google search.)

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    $\begingroup$ Dogs are a good example. We can selectively breed to bring out traits. The Great Dane has been bread for size. They do not live much beyond 12 years, so sometimes there is a cost for this selective breeding. But we can make substantial changes in an animal with 10 or 20 generations. However, we cannot bring out a trait that isn't there. We cannot suddenly turn crocodiles into bird-hipped raptors, and then into birds by selective breeding. This would take intelligent design or millions of years. $\endgroup$ Commented Mar 16 at 11:00
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    $\begingroup$ @RichardKirk: Ornithischian (= bird-hipped) dinosaurs are extinct. Birds are (descended from) saurischian (= lizard-hipped) dinosaurs. More specifically, birds are (descended from) maniraptoran theropod saurischians. $\endgroup$
    – AlexP
    Commented Mar 16 at 14:28
  • $\begingroup$ Thanks for your answer. I had the sense that "Darwinian" wasn't quite the word I was looking for. I meant, simply, evolutionary theory as it's currently understood. $\endgroup$
    – Batperson
    Commented Mar 16 at 21:18
  • $\begingroup$ Basically, I'm hoping to include something that would be surprising and unexpected to present-day biologists (or at least, interested lay people). Not inconsistent with evolutionary theory as biologists understand it, but possibly going a little further and suggestive of additional mechanisms of evolution that aren't currently known of. So it can't be too radical (crocodiles into raptors) but needs to go a little further than chihuahuas vs. great danes. $\endgroup$
    – Batperson
    Commented Mar 16 at 21:28
  • $\begingroup$ @RichardKirk we cannot bring out a trait that isn't there. This would take intelligent design or millions of years. I think the surprise I'm looking for is an example of a new trait appearing, in a way that doesn't take millions of years or intelligent design, and is still not a complete revision of evolutionary theory. $\endgroup$
    – Batperson
    Commented Mar 16 at 21:34

Evolution is, by definition, a generational process. "Extremely rapid" evolution as you're looking for is normally only practical with something that breeds quickly and can have at least a dozen generations in your time frame, preferably more. Given a window of 30 years or so, anything slower to mature than dogs simply won't have enough time to exhibit significant changes; even then, dogs show changes quickly because we artificially select for specific traits, and nature isn't directed with that sort of precision. It's also best noted that natural selection is bounded by whatever traits are present in the species, which are added to via random mutations and are usually incremental changes: no amount of selection pressure can reinforce a trait that simply isn't present.

The biggest driver of change in evolution is simple natural selection: whatever survives to breed, those traits get passed down. Over time, those traits that maximize the odds of surviving to reproduce and/or the number of offspring that themselves survive to reproduce will become more widespread than those that don't. This is rather statistical in nature, meaning that exceptions happen: nothing stops the theoretical "perfect" animal (which doesn't actually exist, as you can't optimize for everything at once) from getting hit by a car, for instance, and detrimental mutations can still proliferate if the detriment is relatively minor or becomes an asset in terms of sexual selection (peacock tails being a good example of the latter). Obviously, this is a slow process, and it's worth noting that the "best" traits change with the environment and other factors: thick fur for instance is very useful in cold regions, but probably a liability in tropical climates.

However, the speed of evolution and natural selection can be altered: they're based on outside pressures, and the strength of those forces is not constant. Relatively mild outside forces (a slightly colder winter) won't apply nearly as much selection pressure as sudden/severe changes (a volcanic winter or, for enduring pressure, an ice age). In the latter case, you can effectively see evolution within just a few generations, provided that the key trait(s) in question were present in the species' genetic pool in some individuals. However, that occurs because the trait in question has become critical for survival, implying that those without the trait died off: you're usually invoking an extinction-level event for the species.

Antibiotic-resistant bacteria are a good example for rapid evolution. Antibacterial soaps and the like advertise a 99.9% kill rate or something similar, but it means the remaining 0.1% is still around to reproduce itself. Use those antibiotics too frequently, and eventually that 0.1% is all that's left to breed, at which point the antibiotic is useless and the bacteria in question will eventually proliferate to its former population levels. Notice that hideous casualty rate, however: this is effectively selecting for a specific trait by killing off everything else.

As applied to your situation, then, you could potentially have birds (or other fast breeders) that exhibit significant differences from those seen twenty years before, mostly via exaggerating some latent trait that was previously too minor to be noticed. However, there's going to be far fewer of them, and you most likely won't see the old form in any number outside of nature preserves, zoos, etc.; to force sufficiently rapid evolution, some catastrophe or major environmental change probably wiped out 90% of the birds within a few years and left the remaining 10% to pass down whatever critical trait your story desires.

PS: As AlexP notes in his answer with dog breeds, "species" is inherently a vague boundary. The most practical definition is that two creatures are of the same species if they can produce fertile offspring together: by this measure, wolves and dogs are one species. You're not realistically going to get that level of separation between your new creatures and the old ones: they'd still be capable of interbreeding, whether or not they actually do so.


I see one option that straddles the line between evolutionary pressure and "intelligent design", that could result in rapid evolution:


Specifically, parasites of the reproductive system.

There exist types bacteria (like some species of Wolbachia) that can hijack the reproductive system of an animal, causing it, among other things to:

  • be unable to reproduce with non-infected members of its species
  • trigger parthenogenesis/self-impregnation without sperm
  • kill male embyos
  • even cause male embryos to turn female, or pseudo-female

Effectively, the bacteria can forcibly speciate a new branch of animals. The new species is all-female, breeds asexually, and is very genetically narrow (possibly daughters of the same original female).

The Wolbachia does it because it needs egg cells to live in, and males with their sperm are useless for it.

IRL, this types of bacteria only infest simple worms and occasionally insects and crustaceans, but there is no reason why your world cannot have a version that affects every animal from an ant to a human, basically making an "Amazon" version of every species, that would only create females, most of whom would be effective clones of their original infected mother.

Such Amazon animals would pretty much instantly become separate species, would be completely inbred (as their mother is ALSO their father, there is zero genetic diversity), and all their mutations that are not instantly deadly would be carried forward, as there is no way to lose them.

This means that some lineages of the "Amazon species" would quickly die out, and others, better suited for the changing environment would evolve these useful traits at the top possible pace (again, being a clone of your mom+ mutation is the fastest possible way to selectively breed.)

More worryingly, a completely asexual species can in some cases breed faster than sexual species. There is no mating needed, every Amazon female self-impregnates as quickly as it physically can.

In 100 years, even slow breeding animals like humans would have the Amazon-species outbreed the sexual breeders, since every Amazon would be pregnant almost every year since the dawn of puberty, while non-infected women only have a few kids.

With faster breeding species like rats, mice, locusts, most fish etc, the Amazons would wipe out their sexual counterparts within few years, and then weirdly mutate to fill specific niches or die out.

Also, specifically to your idea of extraterrestrial life: the ET bacteria might in fact be the Universal Amazonificator, and the trait that the new species evolve for would be the ability to eat other extraterrestrial, or ET-mutated creatures.

  • $\begingroup$ This is interesting, and frightening. I'll have to give it some thought. Thanks! $\endgroup$
    – Batperson
    Commented Mar 18 at 19:50
  • $\begingroup$ It's worth noting that breeding as quickly as possible isn't necessarily the best strategy. You become much more likely to run out of available resources (food, mainly) and be left unable to feed everybody as the number of children you're caring for increases. Infant mortality was high in pre-industrial humanity, but those losses mean a significant waste of energy/resources: imagine how much higher those losses (or maternal mortality!) would be if mothers were automatically pregnant every year. Still, you are correct in noting that asexual breeders, as a rule, usually have more offspring. $\endgroup$
    – Palarran
    Commented Mar 19 at 19:02

I would start by thinking of what drives evolution, which is really change in the frequency of a genotype or phenotype of a population, and what could speed this up. So as other mentioned above, new traits are introduced through mutation, recombination, or breeding among previously separated populations. For mutation, chemicals, radiation, etc increase the background mutation rate. For recombination, bacteria and viruses can transfer genes among species. I like the idea someone gave about bioterrorism. Add in 2 closely related species previously isolated (like grizzly and polar bears) that are suddenly in proximity and you have some good sources of "new" genetic material. Then you need selection to put a lot of pressure on the trait, ie, it needs to be adaptive, and it needs to spread through the population rapidly. Something related to sexual selection? Maybe one of the outcomes is reproducing multiple times per year (or doubling the number of young or the survival of young).Some isolation, maybe through geography or sexual selection and the lack of genetic mixing will quickly result in evolution.

  • $\begingroup$ I just realized a lot of this is covered in Galapagos by Kurt Vonnegut, he has humans evolve extremely rapidly based on almost all of the above. $\endgroup$
    – BirdNerd
    Commented Mar 17 at 4:01

Hybrid speciation In general, natural selection can be very fast, but speciation is very slow and is often thought to require that two species be geographically or at least ecologically separated for some time.

However, hybrid speciation can occur when two different species somehow manage to viable offspring. The offspring have a unique hybrid genome and are unable to breed with either parental species. If they survive inbreeding with each other, a new species is formed. Most. Common in plants, it is thought to have occurred in birds.


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