I need to spay, or neuter my dog, right?

When he is young, of course?

 Everyone is doing it...

Obviously, smart people looked into it.

So there is no need for us to research it, right?

 But wait ... what if someone told you it wasn't okay?

What if, it significantly

affected your dog's natural growth? 

What if it put your dog's health at risk? 

And affected your dog's bone structure?

Just like this brother and sister pictured above. They are from the same litter, and one year old. The lanky one is the boy .... or at least, he was! His sister is still not finished growing, but without testosterone, read about what is happening to his body below.

What if THAT isn't the worst of it?

A study on Golden Retrievers reveals the following;
"Of early-neutered males, 10 percent were diagnosed with HD [Hip Dysplasia], double the occurrence in intact males. There were no cases of CCL [Knee injury, requiring surgery] diagnosed in intact males or females, but in early-neutered males and females the occurrences were 5 percent and 8 percent, respectively. Almost 10 percent of early-neutered males were diagnosed with LSA [Cancer], 3 times more than intact males. The percentage of HSA [Cancer] cases in late-neutered females (about 8 percent) was 4 times more than intact and early-neutered females. There were no cases of MCT [Mass Cell Tumours] in intact females, but the occurrence was nearly 6 percent in late-neutered females."

If it is so healthy for a mammal to be "fixed", why don't we preemptively spay and neuter humans?

Could you find even one physician who would recommend an ovariohysterectomy for a healthy human child?

Why not?