这里的 grow to be so large 中 to be 最好不要去掉。 grow to be so large 和 grow so large 在意思上有差别。

例如：新概念英语第二册有一句：

Three factors have caused these fish to grow so large：the warm water round the hot oil pipes under the sea. Three factors have caused these fish to grow so large: the warm water round the hot oil pipes under the sea; the plentiful supply of food thrown overboard by the crews on the rigs； the total absence of fishing boats around the oil rigs. As a result, the fish just eat and eat and grow and grow in the lovely warm water. Who eats who？这些鱼能长得这么大是由3个因素造成的：海底热的输油管道附近的温暖的海水这些鱼能长得这么大是由3个因素造成的：海底热的输油管道附近的温暖的海水；钻井平台工作人员抛到海里充足的食物；钻井平台周围根本没有捕鱼船只。结果是，这些鱼就在可爱的温暖的水流中吃呀吃，长呀长。究竟谁吃谁呢？

作者用grow so large表达了这些鱼吃呀吃，长呀长，还要持续长，如果用 grow to be so large则暗含着就长这么大了，持续长得可能性很小很小。

问题中and前叙述一个事实The jawbone didn’t have to do as much work，颚骨在进化过程中，功能逐渐减退，于是进化的结果就是so didn’t grow to be so large。颚骨大小就这样“固定”了，不可能再明显持续发展了。本身系动词be就有表达“固定”状态味道，例如：

I live in a very old town which is surrounded by beautiful woods.

我住在一个由美丽的树林环绕的古老的小镇上.

Time is tricky. 时间真是不好对付。

请细细品味下边一句：

When did he grow to be so tall? 他什么时候长得这么高了？