What this later points out is that, even though 2/7 survived, the 2/7 will survive longer than the 1/2. Small families will not be exposed to danger as frequently as larger families, thus the larger families lose more of the children, but the survivors learn how to better prepare for dangerous situations, and how to avoid it.
This actually is heavily observed in nature. Many animals opt for power in sheer numbers rather than expend too much energy and time in raising one or two. Sea Turtles for example poop out hundreds of eggs, but the ratio of those that survive to adulthood is INCREDIBLY tiny. Some stats roughly state about 1 out of 1000 sea turtles survive to adult hood. Yea suddenly yukkuri survival rate doesn't seem that bad. Many turtle babies don't even touch sea water!
Even humans for the vast majority of our history have opted to have as many kids as possible. It was probably only in the last 100 years that the idea of the nuclear family was created and even then it is primarily restricted to first world nations (mainly due to child labor laws, suddenly kids stopped making money and started to cost money!).
But perhaps unexpectedly, infantile stage only, the ones with lots of siblings have higher rate of survival.EnemyOthersThey don't consider such human sensibilities. (Of course strays and wild herds have that direction of raising)2 weeks after birth yukkuri baby death cause
(Wild ones as investigated by Factory)Self DestructionParent's foolish mistakeSibling murderThen from the start wouldn't it be better to only have 1-2 and lavish attention on it? Isn't it a waste if the food and labour were wasted?