Are We a New Species Yet? How About Now?

 

I think the rate of speciation depends on the variables involved, and what type of speciation it is. Obviously, speciation cannot occur overnight, but it also doesn't have to take centuries at a time; it's a highly variable process.

I think sympatric speciation takes longer than allopatric, with parapatric speciation occurs quickest of all.  For an example of parapatry, the fish in the R assignment could either move back to NS waters, adapt to the S waters, or die. Every instance of breeding in the population results in either the adaptation for S waters, or no adaptation, and it divides the populations relatively quickly. Diversification has the possibility to occur in a matter of a few generations. Is that always the case- no, but it is theoretically possible. 

Allopatric speciation I think would generally be the next quickest, but there is a catch. An example of allopatry are the different squirrels in the Grand Canyon. The formation of the Canyon itself (plus the river running through it) separated the native squirrel population. Over time these squirrels differentiated in their genes enough where inbreeding is impossible, even if it was possible for these squirrels to cross a canyon and a very large river to get to each other. I say there's a catch with allopatric speciation, because it takes reintroducing the two separated populations together again to truly know if they are different species or not. Sometimes, like with the squirrels, they come back together and can't interbreed- new species. However, it is possible for them to meet back up and still be able to interbreed. Now this situation can go two ways: 1) they form low fitness hybrids that are infertile and die off, still leading to two distinct species, or 2) they begin interbreeding again and possibly have different morphs of the same species (sometimes they can choose not to interbreed based on sexual preferences, which could then again lead to speciation). If populations take the simple allopatry route, it could take longer than parapatry, but generally still shorter than sympatric I would think.

Now sympatric speciation. This one is hard for me to wrap my head around, and from my research, is kind of rare in nature (at least in multicellular organisms). Sympatric speciation is when two identical populations in identical ranges (so technically one population) speciate despite the absence of a geological barrier. Interbreeding is going to occur at almost every step of this type of speciation, and that is why I think it would take the longest. It's taking one step forward, and two steps back. An example of this I did find was a cichlid (a type of fish) found in a volcanic crater lake in Tanzania. There's two morphs of this fish, a yellow-green that lives near the shore, and a bluish-black morph that lives near the bottom of the lake. After examining these two morphs' DNA, the researchers discovered that they were not necessarily two species yet, but were different enough genetically that they were in the process. Because this lake is so small and secluded, it couldn't be any other type of speciation than sympatric. When you think about how long that lake has been secluded, and that they still aren't two distinct species yet, you begin to see just how long sympatric speciation takes.   

Here's the scientific article if you're interested: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4700518/