Years ago, I had done this with a replica prehistoric American atlatl. The only real difference was that the atlatl had a weighted, cupped handle instead of a hook and the spear was much heavier. I expected the performance to be nearly the same.
I took aim at the 15 yard kangaroo target and hit it in the head although I was actually aiming at the body. The young Aborigine then told me to try the 50 yard target but he would throw first. At that distance I was expecting to see him make a high arching throw. Much to my amazement his trajectory was almost perfectly flat all the way to the target.
I then took my throw and arched it high into the air. I hit near the target with the spear sticking into the ground at about a 45 degree angle. I was told that this wasn't proper form. He then demonstrates by making another level throw. I know from physics that something is going on here which I didn't yet understand.
Another Aborigine comes over and makes the 50 yard throw with even more velocity. This time the spear actually drops about two feet in mid flight and then rises back up and nails the target right in the center of the body. My instructor then explains the technique.
I was told to aim right at the target regardless of the range but release the spear so that it flies with the point about 6 inches higher than the tail end. At that time, I realized that they were actually gliding the spear through the air to the target. They were getting aerodynamic lift to counter gravity and the slender spear's minimal air resistance helped it retain velocity down range. After several more attempts I also succeeded in throwing a couple level trajectories out to 50 yards.
I knew that the boomerang was an ingenious aerodynamic weapon and now I understood that their spear thrower was also. A young strong Aborigine hunter could probably throw a level trajectory out to 60 or 80 yards. They had refined the weapon to exceed the range of the heavier American atlatl and increased the velocity to nearly what would be expected from a primitive bow and arrow.
Kangaroos and emus are relatively large animals with a tall vertical profile. To be able to make a level throw through a group of these animals out to 50 yards and beyond would have been a very desirable feature. The odds of a hit would increase dramatically.
By comparison, the arching trajectory from a bow and arrow would limit which animals were in range. Add to this, the fact that the lethal impact of a 7 foot spear would far surpass that of a much smaller arrow. Even if the spear didn't hit a vital organ, the animal would quickly tire dragging it around and could be easily tracked down. The genius and creativity of the Aborigine was very apparent. At this point, my modern 70 lb. compound deer hunting bow didn't look so superior to the 10,000+ year old weapon. It's no wonder that the Aborigine didn't move on to the bow and arrow.
No. I'm not ready to give up my compound bow. I think it would be difficult to use a spear thrower while sitting in a deer stand. But for the skillful Aborigines and the game they hunted, it's easy to see why they had little reason to change over the millenniums.