> would let itself be a surrogate for raising a cuckoo's young. I don't find it surprising at all. Imagine a mother from the earliest humans, not equipped wit

> would let itself be a surrogate for raising a cuckoo's young. I don't find it surprising at all. Imagine a mother from the earliest humans, not equipped with complex language, formal education, or a civilization-- gives birth. Somehow an infant chimp is slipped into her lap along with her own baby. Both babies look weird, one is strangely hairless one is strangely harry. Both cling on and nurse. Seems obvious to me that mom is going to try to tend to both babies. And a chimp isn't evolved to be a human brood parasite. If it were it would be more similar to humans in whatever ways mattered to the instincts and perceptions of the host (but not necessarily look very similar to a third party species). So if you could at least imagine this working on a primitive human, then it's not at all surprising that it works on some birds. In some sense you could see that capacity for raising a foreign young as itself a sign of intelligence: A highly unintelligent species would only raise its young in ways triggered by an extremely narrow and exact set of signals, while a more intelligent species may be more able to accommodate the differences and figure out how to make things work even when they're not quite right. Think of all the scams modern humans fall for that can be warded off by "hey, watch out for scams that look like xyz". In both the birds case and the early pre-language human case, no one could have warned them that they might be exploited by impersonator babies.