What's that got to do with homosexual animals?

Cosmic background radiation doesn't seem altogether relevant to me.

I'm intrigued by your question:

"If your belief is true, then how come humans didn't develop into something more intelligent and physically different than us today?"

Do you actually understand the notion of evolution?

What you are asking is 'why are modern humans not more modern?' - modern humans are the current END-POINT of our evolutionary journey.

Before asking that question it would help if you familiarized yourself with the fossil record:

Homo habilis
Homo rudolfensis
Homo ergaster
Homo georgicus
Homo erectus
Homo cepranensis
Homo antecessor
Homo heidelbergensis
Homo rhodesiensis
Homo neanderthalensis
Homo sapiens
Oreopithecus
Paranthropus
Australopithecus
Orrorin
Kenyanthropus

You'll find a neat little wikipedia page for each of our ancestors.

After reading that you will then see that humans HAVE evolved into more modern animals than their ancestors.