The fact that giraffes have long necks is commonly known. But what might surprise some people is that it wasn't always this way, and there are many theories why.
Jean-Baptiste Lamarck, a now-famous French scientist who worked to understand evolution better, had a theory that through enough stretching while reaching for leaves, giraffes would start to evolve into longer-necked creatures. This was a good guess, but Lamarck's theory has one major flaw.
One analogy to this theory can explain its flaw; if a pregnant woman broke her arm, her child would then be born with a broken arm, too. This wouldn't actually happen, however, because “broken arm” isn't in the child's genes. Rather, it's just a circumstance that happened to the pregnant woman at one point during her life. Likewise, if a giraffe did manage to stretch its neck during its lifetime, this characteristic wouldn't automatically pass onto her offspring. Simply put, this trait or factor isn't in the offspring's genes.
In the early 1800's, when Lamarck first theorized this notion, society had very little knowledge about how genes worked, thus making his theory seem relatively plausible. But now that researchers have discovered more about what characteristics living beings can actually pass on to their children, this theory has been proven incorrect.
Charles Darwin's theory was far closer to the truth. An English naturalist and geologist who theorized in the same century as Lamarck, Darwin believed that there were both long and short-necked giraffes; but because the long-necked ones could reach more leaves, they lived longer and ultimately had more offspring. Because of this, Darwin posited, there were eventually more long-necked giraffes than short-necked ones.
Darwin's theory hit on a key idea. Originally, when giraffes first existed, there were many different families of them. These families had different neck lengths, though there weren't many differences between the individual giraffes—most were an average height. It wasn't until about 7.5 million years ago that a noticeable difference emerged between the families. Specifically, two families—the Samotherium and Pelaeotragus—started to get longer neck vertebrae in the front half of their necks. In the last two million years, the Giraffa family developed elongated neck bones in the back half of their vertebrae. This is evidenced by today's giraffes.
Some of the short-necked families, mainly the Siviatherium and the Bramatherium, have survived, thus giving us the short-necked giraffes present today. Because of this, there is large variation in giraffe neck length today compared to in the past.
The phenomenon of the giraffe's neck is nothing if not unique. This history reveals a lot about evolution and the different ways it can affect certain creatures.
[Source: National Geographic]