Attachment theory's success comes from more than the generation of a good idea. So many fields have taken to attachment because of the nature of Bowlby's scholarship. Psychology was well along its trajectory away from traditions of ethology when the British psychiatrist-psychoanalyst was at work, but unlike others, he maintained a cross-species fluidity reminiscent of Charles Darwin and his work on continuity in the animal kingdom. Bowlby's discourse on attachment effortlessly weaves together macaque, geese, and human social behaviour in his vivid and compassionate discussions of infant-parent relationships.

As to why trans-species perspectives are born only to fade from science's narrative is a good question and a topic for later discussion. However, it is unlikely that this disappearing act will repeat. Now that neuroscience has joined the mix, attachment theory is firmly accepted as an evolutionary (trans-species) mechanism that is common but not necessarily exclusive to our vertebrate kin.

In moving past disciplinary bounds, attachment theory has penetrated from without to within. Relational bonding between child and parent, portrayed so lovingly in the paintings by Picasso and Cassett, is more than "psychobiological attunement with the infant's cognition or behaviour", writes neuroscientist-psychoanalyst Allan Schore. Socioaffective face-to-face coordination orchestrated through visual, somatic and prosodic cues is a mother's "regulation of the infant's internal states of arousal, [and] the energetic dimension of the child's affective state." Yes, there is a reason, neuroscience nods, why sentimental tunes such as Loewe's resonate. Syncopation of gesture, glance, tone, and touch is echoed somatically in the pulse of psychophysiology. We are born to tune and be attuned to each other.

These findings are a huge boon in the quest to resolve science's ambivalence and contradictory attitudes toward species' similarities and differences. Now that we animals have accepted that we all have more or less the same brains, we can get down to figuring out things like: if birds have brains and cultural habits similar to humans such as flocking and defensive behaviour, why haven't they have descended upon humanity in vengeful ways, as in like Alfred Hitchcock's darkly imagined The Birds? After all, modern humans do this to each other and other animals. Or: why don't modern humans self-regulate their populations and resource consumption as many indigenous human cultures have done? Enter Bowlby and friends, stage left.

Attachment theory helps us understand how to approach the concept of difference from the perspective of sameness. Come again? That is correct—we can be different and the same at the same time. Attachment, or more accurately as Schore points out, relational regulation of the brain-mind-body, helps us see the differences between a New Yorker, a cat, and a grizzly bear not as categorical, but as a product of interactive processes of differentiation. The world's rainbow of psychologies and behaviours (and critically what we make of these so-called differences) derive from what experience (nurture) does with its starting material (nature) through relationships (attachment). Who we each become is a fine blend of ingredients and processes.

For example, attachment theory explains why researchers found that Congolese communities were more likely to show forgiving behavior toward a transgressor than their French counterparts. It also explains why one elephant who lost his family during a conservation-managed cull succumbed to symptoms of Post-traumatic Stress Disorder (PTSD) and grew up to serial kill rhinoceroses, but another elephant did not.

Attachment and its conceptual doppelgänger, traumatology, also help us understand how and why chimpanzees and humans who have a lot in common genetically, physiologically, and psychologically, are, logically, diagnosed with the same psychiatric symptoms when subjected to torture, and, illogically, discriminated against by science-violating ethical and legal standards. For, whereas researchers are generally comfortable with the idea of physiological and biological continuity (i.e., where differences between bats, cats, humans, and frogs are almost minor idiosyncracies), they are less sanguine when it comes to psychology, or even just the idea of mind and consciousness in species other than humans. Somehow, comparability gets recalibrated in practice when species' lines are crossed.

Rabbits, humans, cats, cockatoos, beagles, and even cockroaches are lumped variously as same or different with as much whimsy as the weather. On one hand, the real-life counterparts of Bugs Bunny, Sylvester, Tweety Bird, Wonder Dog, and Archie are considered to be same-enough to stand in for humans as experimental models in studies spanning stress physiology, psychopharmacology, psychological/relational trauma, neuropsychological development, cultural studies, facial recognition, self-recognition, empathy, reconciliation, social learning, theory of mind, consciousness, tool-use, self-recognition, and (as Alex the famous MIT avian graduate demonstrated) language acquisition. On the other hand, attributes identified in human surrogates that qualify them for experimental sacrifice, ethically disqualify human subjects for research and testing practices. What may be good for the animal goose in scientific experimentation is not good for the human gander, and vice versa. First, there is human-animal mental continuity, then there isn't.

Science, like nature, cannot abide a logic vacuum. So when it encounters puzzles and facts and figures that can't be pushed, pulled, or twisted sufficient to fit what scientists want, then not only do we have a failure to communicate, but the demise of a paradigm. Enter stage right what physicist-cum-philosopher Thomas Kuhn called more colorfully, a scientific revolution.

A scientific shift has been slipping and sliding along for quite some time. One by one, scientists have revolted against Monsieur Descartes' reductionist dichotomies and turned their faces toward the Age of Consilience. Nature versus nurture is now nature and nurture, mind versus body is now mind and body, etc., etc., leading naturally to the biggest merger thus far: humans and other animals together in a species-common model of the mind. Consilience of human knowledge has led to re-conciliation with other animals.

Preeminent neuroscientist-primatologists of the likes of Robert Sapolsky and Frans deWaal urge us to look to the other animals' cultures for living better with one and another. Culture entails social learning of custom, behavior, and critically, knowledge. Subsequently, mental continuity with animal kin implies not only ethical, but epistemic continuity. The chimpanzees, gorillas, parrots, frogs, cats, parrots, mice, and octopi whose neuropsychological and biological attributes have lead to their (ab)use, are now mentally qualified for the roles and responsibility of their (ab)users: leadership in science and knowledge creation.

The new trans-species paradigm is really something new. There are new questions, new objectives, and new ethics to live by. And we can thank a stalwart line of scholars who, by not sacrificing their ethics or intellect to Cartesian splitting, provide us with a rich inheritance to begin partnering with the rest of the animal kingdom.