This is the first Asimov / Silverberg collaberation I've read, and it's hard to see the join. It's certainly a gripping read, even if you can see the end coming. The development of the Neanderthal child is well described, though the Neanderthal passages are less convincing. The main weakness is that it's rather over-burdened with dialogue; much of the plot moves by conversation. Those liking a more action packed sci-fi story might find this a little dull. But I had to keep reading to get to the end as soon as possible.