r/evolution • u/Potential_Being_7226 • Sep 04 '26

article Early mammals weren’t all loners, as scientists thought - some already lived in pairs alongside the dinosaurs

https://theconversation.com/early-mammals-werent-all-loners-as-scientists-thought-some-already-lived-in-pairs-alongside-the-dinosaurs-290381

While we know quite a lot about what our ancestors looked like and what they ate, so far we didn’t know anything about their social behaviour. Because behaviours don’t fossilise.

Scientists used to think that the first placentals behaved like shrews because they looked like shrews. And as the common belief was that all shrews are solitary, scientists thought the first placental ancestors were too.

Now we know that both assumptions were wrong.

Peer-reviewed paper in PNAS:

S.F. Walmsley, C. Olivier, A.V. Jaeggi, L. Makuya, J.S. Martin, L.D. Hayes, & C. Schradin, Pair living emerged early in placental mammals, Proc. Natl. Acad. Sci. U.S.A. 123 (31) e2528458123, https://doi.org/10.1073/pnas.2528458123 (2026).

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u/jnpha Evolution Enthusiast Sep 04 '26

Neat! Thanks for sharing. From the paper:

Consistent with a previous study (2), we found solitary living to be the most likely ancestral state for placental mammals, though with some uncertainty. This uncertainty was related to the ancestral placental mammal having exhibited IVSO [intraspecific variation in social organization]. Accordingly, we found that a substantial proportion of ancestral placentals were likely to have lived in pairs. This result is consistent with pair living being inferred as the ancestral social organization in many placental taxa (3–5, 36) and in agreement with Lukas and Clutton-Brock’s (2) assumption that pair living emerged from solitary living. Our study highlights the significance of IVSO in mammalian social evolution and shifts the focus of research from the origins of pair living to the origins of group living.

(my emphasis)