The constellations–not just the zodiac, but all constellations–are not scientifically significant. The stars within any given constellation do not have any relationship with each other; the pattern just happens to look like a ram or a bull or whatever to us. And the pattern itself is random; not all cultures view the same objects among the same stars. But these constellations can be an easy shorthand for astronomers to locate a specific region of the sky quickly.