Oxytocin: Coevolution of human and domesticated animals

  • Yu. E. HerbeckEmail author
  • R. G. Gulevich
  • D. V. Shepeleva
  • V. V. Grinevich


The neuropeptide oxytocin (OT) and its homologs are produced in specialized neurons located in vertebrates exclusively in a deep and evolutionarily old part of the forebrain, the hypothalamus. The axons of OT neurons form the classical hypothalamic-neurohypophyseal tract terminating in the blood vessels of the neurohypothysis to release OT into the system’s blood circulation. However, as was recently demonstrated in mammals, collaterals of OT axons concomitantly project to various forebrain regions to modulate the activity of the local networks. At the behavioral level, OT facilitates intraspecific social contacts in mammals via various mechanisms ranging from the suppression of neuroendocrine stress responses to direct OT action on the neurons of the socially relevant brain regions. Recent reports have indicated the possible contribution of OT to the formation of a social bond between domesticated mammals (dog, sheep, cattle) and humans. Indeed, the social interaction between humans and domesticated animals resulted in the elevation of peripheral OT levels (in blood, saliva, or urine) and, in congruence, exogenous (intranasal) OT application led to more frequent contacts between the owner and the domesticated animal. It has been known for decades that domesticated animals exhibit profound socio-communicative abilities accompanied by suppressed aggression and stress responsiveness. These peculiarities of their behavior and physiology may be influenced by the activity of the central OT system. Therefore, in the present mini review, we focus on the role of OT in the orchestration of distinct forms of social behavior, including the monogamous bond, maternal care, social memory and recognition, aggression, and anxiety. As a conclusion, we propose possible directions for exploring the OT contribution to the empathy between humans and domesticated animals, which was likely established in the course of their coevolution during last 10000–15000 years.


oxytocin evolution domestication silver fox dog wolf human-animal bond 


Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.


  1. Alves, E., Fielder, A., Ghabriel, N., Sawyer, M., and Buisman-Pijlman, F.T.A., Early social environment affects the endogenous oxytocin system: A review and future directions, Front. Endocrinol., 2015, vol. 6, no. 32. doi 10.3389/fendo.2015.00032Google Scholar
  2. Bülbül, M., Babygirija, R., Cerjak, D., Yoshimoto, S., Ludwig, K., and Takahashi, T., Hypothalamic oxytocin attenuates CRF expression via GABA(A) receptors in rats, Brain Res., 2011, vol. 1387, pp. 39–45. doi 10.1016/j.brainres.2011.02.091CrossRefPubMedGoogle Scholar
  3. Bartz, J.A., Zaki, J., Bolger, N., and Ochsner, K.N., Social effects of oxytocin in humans: Context and person matter, Trends Cogn. Sci., 2011, vol. 15, pp. 301–309. doi 10.1016/j.tics.2011.05.002PubMedGoogle Scholar
  4. Belyaev, D.K., Destabilizing selection as a factor in domestication, J. Hered., 1979, vol. 70, pp. 301–308.CrossRefPubMedGoogle Scholar
  5. Belyaev, D.K., Destabilizing selection as a factor of domestication, in Genetika i blagosostoyanie chelovechestva (Genetics and Welfare of Humankind), Moscow: Nauka, 1981.Google Scholar
  6. Benelli, A., Bertolini, A., Poggioli, R., Menozzi, B., Basaglia, R., and Arletti, R., Polymodal dose-response curve for oxytocin in the social recognition test, Neuropeptides, 1995, vol. 28, no. 4, pp. 251–255. doi 10.1016/0143-4179(95)90029-2CrossRefPubMedGoogle Scholar
  7. Bondar’, N.P. and Kudryavtseva, N.N., Violation of social recognition in male mice with repeated experience of aggression, Zh. Vyssh. Nervn. Deyat. im. I. P. Pavlova, 2005, vol. 55, no. 3, pp. 378–384.Google Scholar
  8. Bosch, O.J. and Neumann, I.D., Both oxytocin and vasopressin are mediators of maternal care and aggression in rodents: From central release to sites of action, Horm. Behav., 2012, vol. 61, no. 3, pp. 293–303. doi 10.1016/j.yhbeh.2011.11.002CrossRefPubMedGoogle Scholar
  9. Bradshaw, J.W.S. and Paul, E.S., Could empathy for animals have been an adaptation in the evolution of Homo?, Anim. Welfare, 2010, vol. 19, pp. 107–112.Google Scholar
  10. Briine, M., On human self-domestication, psychiatry, and eugenics, Philos. Ethics Humanit. Med., 2007, vol. 2, p. 21. doi 10.1186/1747-5341-2-21CrossRefGoogle Scholar
  11. Calcagnoli, F., de Boer, S.F., Althaus, M., Boer, J.A., and Koolhaas, J.M., Antiaggressive activity of central oxytocin in male rats, Psychopharmacology, 2013, vol. 229, pp. 639–651. doi 10.1007/s00213-013-3124-7CrossRefPubMedGoogle Scholar
  12. Calcagnoli, F., Meyer, N., De, B.S.F., Althaus, M., and Koolhaas, J.M., Chronic enhancement of brain oxytocin levels causes enduring anti-aggressive and pro-social explorative behavioral effects in male rats, Horm. Behav., 2014, vol. 65, pp. 427–433. doi 10.1016/j.yhbeh.2014.03.008CrossRefPubMedGoogle Scholar
  13. Cho, M.M., DeVries, A.C., Williams, J.R., and Carter, C.S., The effects of oxytocin and vasopressin on partner preferences in male and female prairie voles (Microtus ochrogaster), Behav. Neurosci., 1999, vol. 113, pp. 1071–1079. doi 10.1037/0735-7044.113.5.1071CrossRefPubMedGoogle Scholar
  14. Darwi., Ch., The Expression of the Emotions in Man and Animals, Oxford University Press, 2009, 4th ed.CrossRefGoogle Scholar
  15. de Boer, S.F., Van Der Vegt, B.J., and Koolhaas, J.M., Individual variation in aggression of feral rodent strains: A standard for the genetics of aggression and violence?, Behav. Genet., 2003, vol. 33, pp. 485–501. doi 10.1023/A:1025766415159CrossRefPubMedGoogle Scholar
  16. de Dreu, C.K.W., Greer, L.L., Kleef, G.A.V., Shalvi, S., and Handgraaf, M.J.J., Oxytocin promotes human ethnocentrism, Proc. Natl. Acad. Sci. U.S.A., 2011, vol. 108, pp. 1262–1266. doi 10.1073/pnas.1015316108CrossRefPubMedPubMedCentralGoogle Scholar
  17. de Jong, T.R., Beiderbeck, D.I., and Neumann, I.D., Measuring virgin female aggression in the female intruder test (fit): Effects of oxytocin, estrous cycle, and anxiety, PLoS One, 2014, vol. 9. doi 10.1371/journal.pone.0091701Google Scholar
  18. de Waal, F.B.M., Putting the altruism back into altruism: The evolution of empathy, Annu. Rev. Psychol., 2008, vol. 59, pp. 279–300. doi 10.1146/annurev.psych.59.103006.093625CrossRefPubMedGoogle Scholar
  19. Domes, G., Heinrichs, M., Glascher, J., Buchel, C., Braus, D.F., and Herpertz, S.C., Oxytocin attenuates amygdala responses to emotional faces regardless of valence, Biol. Psychiatry, 2007, vol. 62, pp. 1187–1190. doi 10.1016/j.biopsych.2007.03.025CrossRefPubMedGoogle Scholar
  20. du Vigneaud, V., Ressler, C., Swan, J.M., Roberts, C.W., and Katsoyannis, P.G., Oxytocin: Synthesis, J. Am. Chem. Soc., 1954, vol. 76, no. 12, pp. 3115–3118. doi 10.1021/ja01641a004CrossRefGoogle Scholar
  21. Eliava, M., Melchior, M., Knobloch-Bollmann, H.S., Wahis, J., da Silva Gouveia Tang, Y., Ciobanu, A.C., Triana del Rio R., Roth L.C., Althammer F., Chavant V., Goumon Y., Gruber T., Busnelli M., Chini, B., et al., A new population of parvocellular oxytocin neurons controlling magnocellular neuron activity and inflammatory pain processing, Neuron, 2016, vol. 89, no. 6, pp. 1291–1304.CrossRefPubMedGoogle Scholar
  22. Ferguson, J.N., Aldag, J.M., Insel, T.R., and Young, L.J., Oxytocin in the medial amygdala is essential for social recognition in the mouse, J. Neurosci., 2001, vol. 21, no. 20, pp. 8278–8285.PubMedGoogle Scholar
  23. Francis, D.D., Champagne, F., and Meaney, M.J., Variations in maternal behavior are associated with differences in oxytocin receptor levels in the rat, J. Neuroendocrinol., 2000, vol. 12, pp. 1145–1148.CrossRefPubMedGoogle Scholar
  24. Goodson, J.L. and Bass, A.H., Forebrain peptides modulate sexually polymorphic vocal circuitry, Nature, 2000, vol. 403, pp. 769–772. doi 10.1038/35001581CrossRefPubMedGoogle Scholar
  25. Grinevich, V., Desarménien, M., Chini, B., Tauber, M., and Muscatelli, F., Ontogenesis of oxytocin pathways in the mammalian brain: Late maturation and psychosocial disorders front, Neuroanat., 2015, vol. 8, p. 164. doi 10.3389/fnana.2014.00164Google Scholar
  26. Grinevich, V., Knobloch-Bollmann, H.S., Eliava, M., Busnelli, M., and Chini, B., Assembling the puzzle: Pathways of oxytocin signaling in the brain, Biol. Psychiatry, 2016, vol. 79, no. 3, pp. 155–164. doi 10.1016/j.biopsych.2015.04.013CrossRefPubMedGoogle Scholar
  27. Hare, B., Plyusnina, I., Ignacio, N., Schepina, O., Stepika, A., Wrangham, R., and Trut, L., Social cognitive evolution in captive foxes is a correlated by-product of experimental domestication, Curr. Biol., 2005, vol. 15, pp. 226–230. doi 10.1016/j.cub.2005.01.040CrossRefPubMedGoogle Scholar
  28. Hare, B., Wobber, V., and Wrangham, R., The self-domestication hypothesis: Evolution of bonobo psychology is due to selection against aggression, Anim. Behav., 2012, vol. 83, pp. 573–585. doi 10.1016/j.anbehav.2011.12.007CrossRefGoogle Scholar
  29. Hernádi, A., Kis, A., Kanizsár, O., Tóth, K., Miklósi, B., and Topál, J., Intranasally administered oxytocin affects how dogs (Canis familiaris) react to the threatening approach of their owner and an unfamiliar experimenter, Behav. Process, 2015, vol. 119, pp. 1–5. doi 10.1016/j.beproc.2015.07.001CrossRefGoogle Scholar
  30. Huber, D., Veinante, P., and Stoop, R., Vasopressin and oxytocin excite distinct neuronal populations in the central amygdale, Science, 2005, vol. 308, pp. 245–248. doi 10.1126/science.1105636CrossRefPubMedGoogle Scholar
  31. Insel, T.R. and Hulihan, T.J., A gender-specific mechanism for pair bonding: Oxytocin and partner preference formation in monogamous voles, Behav. Neurosci., 1995, vol. 109, pp. 782–789.CrossRefPubMedGoogle Scholar
  32. Jensen, P., Behavior genetics and the domestication of animals, Annu. Rev. Anim. Biosci., 2014, vol. 2, pp. 85–104. doi 10.1146/annurev-animal-022513-114135CrossRefPubMedGoogle Scholar
  33. Jurek, B., Slattery, D.A., Hiraoka, Y., Liu, Y., Nishimori, K., Aguilera, G., Neumann, I.D., and Burg, E.H., Oxytocin regulates stress-induced CRF gene transcription through CREB-regulated transcription coactivator 3, J. Neurosci., 2015, vol. 35, no. 35, pp. 12248–12260. doi 10.1523/JNEUROSCI.1345-14.2015CrossRefPubMedPubMedCentralGoogle Scholar
  34. Kirsch, P., Esslinger, C., Chen, Q., Mier, D., Lis, S., Siddhanti, S., Gruppe, H., Mattay, V.S., Gallhofer, B., and Meyer-Lindenberg, A., Oxytocin modulates neural circuitry for social cognition and fear in humans, J. Neurosci., 2005, vol. 25, no. 49, pp. 11489–11493. doi 10.1523/JNEUROSCI.3984-05.2005CrossRefPubMedGoogle Scholar
  35. Kis, A., Bence, M., Lakatos, G., Pergel, E., Turcsán, B., Pluijmakers, J., Vas, J., Elek, Z., Bruder, I., Foldi, L., Sasvári-Székely, M., Miklósi, A., Rónai, Z., and Kubinyi, E., Oxytocin receptor gene polymorphisms are associated with human directed social behavior in dogs (Canis familiaris), PLoS ONE, 2014, vol. 9. doi 10.1371/journal.pone.0083993Google Scholar
  36. Kis, A., Hernádi, A., Kanizsár, O., Gácsi, M., and Topál, J., Oxytocin induces positive expectations about ambivalent stimuli (cognitive bias) in dogs, Horm. Behav., 2015, pp. 1–7. doi 10.1016/j.yhbeh.2014.12.004Google Scholar
  37. Knobloch, H.S. and Grinevich, V., Evolution of oxytocin pathways in the brain of vertebrates, Front. Behav. Neurosci., 2014, vol. 8, p. 31. doi 10.3389/fnbeh.2014.00031CrossRefPubMedPubMedCentralGoogle Scholar
  38. Knobloch, H.S., Charlet, A., Hoffmann, L.C., Eliava, M., Khrulev, S., Cetin, A.H., Osten, P., Schwarz, M.K., Seeburg, P.H., Stoop, R., and Grinevich, V., Evoked axonal oxytocin release in the central amygdale attenuates fear response, Neuron, 2012, vol. 73, pp. 553–566. doi 10.1016/j.neuron.2011.11.030CrossRefPubMedGoogle Scholar
  39. Kujala, M.V., Kujala, J., Carlson, S., and Hari, R., Dog experts’ brains distinguish socially relevant body postures similarly in dogs and humans, PLoS ONE, 2012, vol. 7. doi 10.1371/journal.pone.0039145Google Scholar
  40. Lucht, M.J., Barnow, S., Sonnenfeld, C., Rosenberger, A., Grabe, H.J., Schroeder, W., Völzke, H., Freyberger, H.J., Herrmann, F.H., Kroemer, H., and Rosskopf, D., Associations between the oxytocin receptor gene (OXTR) and affect, loneliness and intelligence in normal subjects, Prog. Neuropsychopharmacol. Biol. Psychiatry, 2009, vol. 33, pp. 860–866. doi 10.1016/j.pnpbp.2009.04.004CrossRefPubMedGoogle Scholar
  41. Meinlschmidt, G. and Heim, C., Sensitivity to intranasal oxytocin in adult men with early parental separation, Biol. Psychiatry, 2007, vol. 61, pp. 1109–1111. doi 10.1016/j.biopsych.2006.09.007CrossRefPubMedGoogle Scholar
  42. Miklósi, A., Kubinyi, E., Topál, J., Gácsi, M., Virányi, Z., and Csányi, V., A simple reason for a big difference: Wolves do not look back at humans, but dogs do, Curr. Biol., 2003, vol. 13, no. 9, pp. 763–766. doi 10.1016/S0960-9822(03)00263-XCrossRefPubMedGoogle Scholar
  43. Nagasawa, M., Mitsui, S., En, S., Ohtani, N., Ohta, M., Sakuma, Y., Onaka, T., Mogi, K., and Kikusui, T., Social evolution. Oxytocin-gaze positive loop and the coevolution of human-dog bonds, Science, 2015, vol. 348, pp. 333–336. doi 10.1126/science.1261022CrossRefPubMedGoogle Scholar
  44. Neumann, I.D. and Landgraf, R., Balance of brain oxytocin and vasopressin: Implications for anxiety, depression, and social behaviors, Trends Neurosci., 2012, vol. 35, pp. 649–659. doi 10.1016/j.tins.2012.08.004CrossRefPubMedGoogle Scholar
  45. Neumann, I.D., Brain oxytocin: A key regulator of emotional and social behaviours in both females and males, J. Neuroendocrinol., 2008, vol. 20, pp. 858–865. doi 10.1111/j.1365-2826.2008.01726.xCrossRefPubMedGoogle Scholar
  46. Nowak, R. and Boivin, X., Filial attachment in sheep: Similarities and differences between ewe-lamb and humanlamb relationships, Appl. Anim. Behav. Sci., 2015, vol. 164, pp. 12–28. doi 10.1016/j.applanim.2014.09.013CrossRefGoogle Scholar
  47. Olazábal, D.E. and Young, L.J., Oxytocin receptors in the nucleus accumbens facilitate “spontaneous” maternal behavior in adult female prairie voles, Neuroscience, 2006, vol. 141, no. 2, pp. 559–568. doi 10.1016/j.neuroscience.2006.04.017CrossRefPubMedGoogle Scholar
  48. Olazábal, D.E. and Young, L.J., Variability in “spontaneous” maternal behavior is associated with anxiety-like behavior and affiliation in na ive juvenile and adult female prairie voles (Microtus ochrogaster), Dev. Psychobiol., 2005, vol. 47, no. 2, pp. 166–178. doi 10.1002/dev.20077CrossRefPubMedGoogle Scholar
  49. Olff, M., Frijling, J.L., Kubzansky, L.D., Bradley, B., Ellenbogen, M.A., Cardoso, C., Bartz, J.A., Yee, J.R., and van Zuiden, M., The role of oxytocin in social bonding, stress regulation and mental health: An update on the moderating effects of context and interindividual differences, Psychoneuroendocrinology, 2013, vol. 38, no. 9, pp. 1883–1894. doi 10.1016/j.psyneuen.2013.06.019CrossRefPubMedGoogle Scholar
  50. Oliva, J.L., Rault, J.-L., Appleton, B., and Lill, A., Oxytocin enhances the appropriate use of human social cues by the domestic dog (Canis familiaris) in an object choice task, Anim. Cogn., 2015, vol. 18, pp. 767–775. doi 10.1007/s10071-015-0843-7CrossRefPubMedGoogle Scholar
  51. Palagi, E., Nicotra, V., and Cordoni, G., Rapid mimicry and emotional contagion in domestic dogs, R. Soc. Open Sci., 2015, vol. 2, p. 150505. doi 10.1098/rsos.150505CrossRefPubMedPubMedCentralGoogle Scholar
  52. Popik, P. and van Ree Vetulani, J.M., Low doses of oxytocin facilitate social recognition in rats, Psychopharmacology (Berl.), 1992, vol. 106, no. 1, pp. 71–74.CrossRefGoogle Scholar
  53. Price, E.O., Animal Domestication and Behavior, Oxon, N.Y.: CABI, 2002.CrossRefGoogle Scholar
  54. Rehn, T., Handlin, L., Uvnas-Moberg, K., and Keeling, L.J., Dogs’ endocrine and behavioural responses at reunion are affected by how the human initiates contact, Physiol. Behav., 2014, vol. 124, pp. 45–53. doi 10.1016/j.physbeh.2013.10.009CrossRefPubMedGoogle Scholar
  55. Rilling, J.K., Demarco, A.C., Hackett, P.D., Chen, X., Gautam, P., Stair, S., Haroon, E., Thompson, R., Ditzen, B., Patel, R., and Pagnoni, G., Sex differences in the neural and behavioral response to intranasal oxytocin and vasopressin during human social interaction, Psychoneuroendocrinology, 2014, vol. 39, pp. 237–248. doi 10.1016/j.psyneuen.2013.09.022CrossRefPubMedGoogle Scholar
  56. Rodrigues, S.M., Saslow, L.R., Garcia, N., John, O.P., and Keltner, D., Oxytocin receptor genetic variation relates to empathy and stress reactivity in humans, Proc. Natl Acd. Sci. U.S.A., 2009, vol. 106, pp. 21437–21441. doi 10.1073/pnas.0909579106CrossRefGoogle Scholar
  57. Romero, T., Nagasawa, M., Mogi, K., Hasegawa, T., and Kikusui, T., Oxytocin promotes social bonding in dogs, Proc. Natl Acad. Sci. U.S.A., 2014, vol. 111, pp. 9085–9090. doi 10.1073/pnas.1322868111CrossRefPubMedPubMedCentralGoogle Scholar
  58. Ross, H.E. and Young, L.J., Oxytocin and the neural mechanisms regulating social cognition and affiliative behavior, Front. Neuroendocrinol., 2009, vol. 30, pp. 534–547. doi 10.1016/j.yfrne.2009.05.004CrossRefPubMedPubMedCentralGoogle Scholar
  59. Scharrer, E., Die Lichtempfindlichkeit blinder Elritzen (Untersuchungen uber das Zwischenhirn der Fische), Z. Vergl. Physiol., 1928, vol. 7, pp. 1–38. doi 10.1007/BF00341151CrossRefGoogle Scholar
  60. Shamay-Tsoory, S.G., Fischer, M., Dvash, J., Harari, H., Perach-Bloom, N., and Levkovitz, Y., Intranasal administration of oxytocin increases envy and schadenfreude (gloating), Biol. Psychiatry, 2009, vol. 66, pp. 864–870. doi 10.1016/j.biopsych.2009.06.009CrossRefPubMedGoogle Scholar
  61. Somatic Transgenesis in Molecular Neuroendocrinology, Wiley and Sons, 2016 (in press).Google Scholar
  62. Staes, N., Stevens, J.M.G., Helsen, P., Hillyer, M., Korody, M., and Eens, M., Oxytocin and vasopressin receptor gene variation as a proximate base for inter- and intraspecific behavioral differences in bonobos and chimpanzees, PLoS ONE, 2014, vol. 9. doi 10.1371/journal.pone.0113364Google Scholar
  63. Trut, L., Oskina, I., and Kharlamova, A., Animal evolution during domestication: The domesticated fox as a model, BioEssays, 2009, vol. 31, pp. 349–360. doi 10.1002/bies.200800070CrossRefPubMedPubMedCentralGoogle Scholar
  64. Trut, L.N., Plyusnina, I.Z., and Os’kina, I.N., An experiment on fox domestication and debatable issues of evolution of the dog, Genetika, 2004, vol. 40, no. 6, pp. 794–807.PubMedGoogle Scholar
  65. Trut, L.N., Plyusnina, I.Z., and Oskina, I.N., An experiment on fox domestication and debatable issues of evolution of the dog, Russ. J. Genet., 2004, vol. 40, pp. 644–655.CrossRefGoogle Scholar
  66. Viviani, D., Charlet, A., Burg, E., Robinet, C., Hurni, N., Abatis, M., Magara, F., and Stoop, R., Oxytocin selectively gates fear responses through distinct outputs from the central amygdale, Science, 2011, vol. 333, pp. 104–107. doi 10.1126/science.1201043CrossRefPubMedGoogle Scholar
  67. Windle, R.J., Kershaw, Y.M., Shanks, N., Wood, S.A., Lightman, S.L., and Ingram, C.D., Oxytocin attenuates stress-induced c-fos mRNA expression in specific forebrain regions associated with modulation of hypothalamo-pituitary- adrenal activity, J. Neurosci., 2004, vol. 24, pp. 2974–2982. doi 10.1523/JNEUROSCI.3432-03.2004CrossRefPubMedGoogle Scholar
  68. Wittig, R.M., Crockford, C., Deschner, T., Langergraber, K.E., Ziegler, T.E., and Zuberbühler, K., Food sharing is linked to urinary oxytocin levels and bonding in related and unrelated wild chimpanzees, P. Roy. Soc. Lond, 2014, vol. 281, p. 20133096. doi 10.1098/rspb.2013.3096CrossRefGoogle Scholar
  69. Yayou, K., Ito, S., and Yamamoto, N., Relationships between postnatal plasma oxytocin concentrations and social behaviors in cattle, Anim. Sci. J., 2015, vol. 86, no. 8, pp. 806–813. doi 10.1111/asj.12363CrossRefPubMedGoogle Scholar
  70. Young, L.J., Lim, M.M., Gingrich, B., and Insel, T.R., Cellular mechanisms of social attachment, Horm. Behav., 2001, vol. 40, pp. 133–138. doi 10.1006/hbeh.2001.1691CrossRefPubMedGoogle Scholar

Copyright information

© Pleiades Publishing, Ltd. 2017

Authors and Affiliations

  • Yu. E. Herbeck
    • 1
    Email author
  • R. G. Gulevich
    • 1
  • D. V. Shepeleva
    • 1
  • V. V. Grinevich
    • 2
  1. 1.Institute of Cytology and Genetics, Siberian BranchRussian Academy of SciencesNovosibirskRussia
  2. 2.Schaller Research Group on Neuropeptides, German Cancer Research CenterCentral Institute of Mental Health and University of HeidelbergHeidelberg, MannheimGermany

Personalised recommendations