…suggesting we need to rethink our understanding of species barriers.

The vagueries of speciation has been especially exploitable by the conservatism/YIMBYism movement, where a trait common in one region but uncommon in others can be used to declare a common unthreatened animal as an endangered species, despite a lack of genetic divergence. It would be like declaring uncommonly red-haired Irish as not just an ethnicity but a separate species.

My favorite example of vagueries in species differentiation is a study that found only 13 genes that reliably differ between domestic cats and European and Near Eastern wildcats. (https://www.pnas.org/doi/full/10.1073/pnas.1410083111) It really brings into question what domestication even is, considering that housecats are perfectly capable of supporting themselves outside of areas inhabited by humans. Their lack of differentiation from wildcats means that they can easily become invasive species in areas where they are introduced by humans.

It's impossible for a species to be invasive to its native land, but Poland has managed to simultaneously consider a group of animals with a mere bakers dozen of genes differentiating them, none of which hinder their ability to interbreed, as both "currently threatened with extinction in their natural habitat" (https://pmc.ncbi.nlm.nih.gov/articles/PMC6749728/) and an "invasive alien species" (https://apnews.com/article/science-poland-wildlife-cats-bird...).

Species boundaries are typically defined by the inability of organisms from either side to mate and produce fertile offspring. There are many problems with that, especially in cases like ring species and species complexes, but there's certainly no accepted interpretation that would allow you to declare red-haired Irish people a separate species.

> Have we ever really defined species barriers?

It's fairly easy to make definitions, and there are several. The real problem is that many biologists for many decades have been confused about whether we are attempting to make pragmatic definitions or whether we are uncovering "true answers" regarding biological discontinuities. It might not seem that bad if you don't consider geographic separation, but when you do, the literature turns into a total mess. The truth is, though it's unpalatable to many, that there's nothing about biological science that implies that the question "are these two geographically disjunct populations members of the same species?" has any particular answer.

From the first article:

>we mapped Illumina raw sequences from a pool of four wildcat individuals [two European wildcats (F. s. silvestris) and two Eastern wildcats (F. s. lybica)].

And the second article talks about the Eurasian lynx (Lynx lynx). It looks like they are very different species (same genus in the first, but only same family in the second). I do not really know how cat classification works, so maybe I miss some basic knowledge of the Felidae?

Technologically, dogs and wolves are the same species, but we can't let dogs replace the niche that was occupied by wolves.

This question is not directed at your example specifically: is there something beyond genetics that can make a species?

My reasoning is: I’ve seen animals lose some of their species’ behavior when separated from their parents too early (for puppies and kittens).

They end up missing behaviors and abilities that seem to be passed generationally rather than innate.

If this is the case, isn’t there something lost when a species is only kept alive domesticated or in zoos? Even if later reintroduced to the wild.

Species are a leaky abstraction. If species worked 100% of the time - evolution would stop.

Evolution and biology works on individuals. Species is just a simplification.