look, it at the end of the day, the idea of species is a made up social construct. it is a very, very useful concept, but like, at the end of the day where you draw the lines of what is a single organism is arbitrary, where you draw the line at what is and is not a deer is made up, and how you define deer is equally as arbitrary as our definition of human. if we want anything to mean anything then we need to come to some vague consensus that things mean things
A species is basically a gene pool that doesn't overlap with other gene pools... but that's difficult to define the boundaries of in many cases because gene pools DO overlap in nature, it's very common in fact.
Hybridization between species is a thing that can happen sometimes. Like if you cross a male donkey with a female horse you get a mule, and mules are infertile. Sooo, are donkeys and horses the same species? Not really. Neanderthals produced viable offspring with homo sapiens, we've found examples of humans with neanderthal genes as little back in their family tree as one of their grandparents. So are neanderthals and homo sapiens the same species? Not really, but I'd say they were both human. but it's a matter of personal opinion more than scientific definition
And then there's "ring species" examples, where adjacent species *can* interbred with nearby populations, except for when there's been a big enough gene divide?
Take this variety of California salamanders, here croceater and eschscholtzii can't interbreed in this example.
this is probably the most well known example, but even within a single species you get geographic gene specialization. Including in humans.
basically, the tree of life, when you zoom in close enough, really is a spectrum. The misconception of people who don't understand evolution is partially because the idea of "species" as hard coded boundaries is very natural for us. We love categories and patterns, and unfortunately for us, nature is just not as simple as we'd prefer it to be. Over both space and time, the boundaries between species is blurry. There is no "missing link" because it was always a gradual series of changes to different populations across the world to begin with. The world is a messy and complicated place, and we're all distant cousins of each other.
The idea of a species isn't a universal axiom, it isn't a law, it isn't a rule. It's just a useful tool, and sometimes in certain cases, it is good to admit that it isn't a one-size-fits-all tool.
sometimes, bacteria just scoop up DNA just floating around minding its own business, and then add it to their own DNA. This is known as horizontal gene transfer, or HGT. It happens all the time, hell, bacteria have been known to occasionally become resistant to some antibiotics by STEALING GENES from OTHER SPECIES of bacteria! The tree of life isn't even a tree! We've done away with that model, it's more accurate to refer to the model as a "braided stream".
And this strange behavior isn't even unique to bacteria, there are examples of plant to plant gene transfer, plant to animal gene transfer, plant to fungus gene transfer, fungus to insect, the list goes on!
While I very much appreciate the notion that gene transfers do happen, I think it's fair to say they happen much more often at "lower" branches, like viruses, but are rather rare in mammals or even plants. So while it's a spectrum, it's an one with local maxima, isn't it?
Can you give some examples? Asking genuinely as a fan, not a protester 😃
@kravietz honestly the wikipedia page for horizontal gene transfer is a good place to start. Scishow also has a video on the subject that I found pretty enlightening, though I forget what it's called
@kravietz while it gets even more rare for HGT the further away two organisms are from each other in terms of genetic variation, it doesn't appear to be hard-limited. It's a probability thing. There are cases known of HGT taking place, in laboratory settings and in nature, in this modern day and age between VERY distant kingdoms. plant to animal gene transfer for instance has happened.