Intelligent machines will not really be built "from scratch" because augmentation of human intelligence by machines makes use of all the same technology as is present is straight machine intelligence projects, plus a human brain. Those projects have the advantage of being competitive with humans out of the box - and they interact synergetically with traditional machine intelligence projects. For details see my intelligence augmentation video/essay.

The thing that doesn't make much sense is building directly on the human brain's wetware with more of the same. Such projects are typically banned at the moment - and face all kinds of technical problems anyway.