Speciation Speed Run

 Darwin was wrong. 

There, I said it! Go ahead and get angry! Feel free to boo, hiss, and chuck those rotten tomatoes you're hiding behind your back. But I'm right. 

As much as we hold Darwin up in the spotlight, the Father of Evolution didn't get it all right. He had no idea what DNA was, for starters. But more relevant today is his take on the speed of speciation. Darwin postulated that it takes centuries, if not millennia, of minor changes to fully separate one species into two. 

But he. Was. WRONG! 

Wild, right? Let's back up a bit, and I'll tell you why. 

When does one species become two? Darwin was right when he theorized that the split usually isn't instantaneous. You never had a chicken pop out of a dinosaur egg. Speciation is a process. You have a dinosaur, who has a slightly feathery dinosaur, who has a slightly smaller and feathery dinosaur, on and on until you eventually have the domestic terror known today as Gallus gallus. 

But if minor changes constitute speciation, then where do we draw the species lines? What makes an offspring different enough from its ancestors to constitute a new species? Without answering these questions, we can't determine how long speciation takes - because we don't know when speciation actually happens! 

Big questions, short blog. Let's speed things up. 

Darwin knew speciation is a process. Populations undergoing speciation grow slowly more distant in location, genes, ability to interbreed, and morphology, until eventually they seem like they were never the same population at all. There are no distinct stages; it's a continuum of "barely separate, kind of separate, almost completely separate". But most scientists agree that the "final" stage, when one species becomes two, is complete lack of interbreeding. Total reproductive isolation. 

Figuring this out in the wild can be a pain. But it also gives us something to measure. Speciation happens however quickly reproductive isolation happens. So then the question becomes, how fast can reproductive isolation happen?

Though he didn't articulate reproductive isolation in quite the same way, Darwin had the right idea. He theorized that it would take a long time for changes that affected reproduction to build up. And scientists thought that way for decades. Then they started to actually look at speciation. And they realized they were dead wrong. 

Reproductive isolation can happen dozens of different ways - premating isolation, postzygotic isolation, premating-prezygotic isolation, and all the individual methods within those categories. Some of those isolation mechanisms can take hundreds of years to form, just like Darwin postulated. But some, it turns out, are a helluva lot faster. 

How much faster? Let's try 20 generations. The speed of ecological speciation by Hendry et. al (https://besjournals.onlinelibrary.wiley.com/doi/full/10.1111/j.1365-2435.2007.01240.x) provides an interesting overview of speciation times in sympatric situations. They conclude that you could have significant differences in just 20 generations, depending on the scenario and the drivers of reproductive isolation studied. That's way faster than expected, even for allopatric species! I mean, 20 generations of bacteria can happen within days. That's way faster than Darwin's millennia! 

Another study, Extraordinarily rapid speciation in a marine fish by Momigliano et. al explores the speciation of European flounders over just 3,000 years. Generation time is roughly 4.2 years for the European flounder (https://www.fishbase.de/summary/1341#:~:text=Generation%20time%3A%204.2%20(2.9%20%2D%206.1)%20years.), which means it only took about 714 generations for speciation! That's, like, hella fast compared to the thousands and thousands of years that Darwin postulated. 

So maybe Darwin was off by a few centuries. Species still takes years for most complex organisms like eukaryotes, right?? 

NOPE. 

What would you do if I told you that some species encounter total reproductive isolation in just one generation? 

Now now, don't go running away yet! It's true! But it's only true because plants are absolutely wild when it comes to genetics. 

The fastest way to create reproductive isolation is to make an organism that cannot reproduce with any other organisms, but can reproduce with itself. Sounds impossible, but it's not. Because sometimes plants do this crazy thing where they duplicate entire copies of their genome. It's called polyploidy. 

Insane, right?! Polyploid plants exponentially increase the size of their genome, mostly by accident. Since you kinda need the same number of chromosomes to mate with something, this causes instant isolation from other plants of their species. The only organism left for our poor polyploid to mate with is itself. If it doesn't die off, generations of self-fertilization, spreading, and accumulating mutation can lead to an entirely new species of plant. And all that from just one generation of change! Talk about rapid speciation. One study I found, entitled The frequency of polyploid speciation in vascular plants by Wood et. al (2009) estimated that "15% of angiosperm and 31% of fern speciation events are accompanied by ploidy increase". That's no small number! 

So how fast is speciation? Sometimes, like Darwin said, it is a long and arduous process. Other times, speciation happens as quickly as you can reproduce. Because biology is wild, nature never has a clean answer, and plants absolutely refuse to make sense. 

God, I love science!