Journey of Life - Seas of Life 5
Steve travels back 3.8 billion years to when life began. Journeying round the oceans, he explores life's first laboratory and discovers how the incredible variety of sea creatures arose, from the first microbes to hagfish and dolphins.
And amazingly ,it's the foundation of our basic body plan, we share the very same head sprouting genes. Flatworms also evolved the very first eyes, just a cluster of cells. They can't do much more than tell light from dark, but at least the worm has some idea what's coming when it's travelling head first. And this new information needed processing. It might be small and very simple, but this is nevertheless the first brain. So it's thanks to the flatworm that our brains are in our heads and not in our backsides.
If the evolution of the first brain was a milestone event, then so too was the evolution of the first anus. Imagine having to get rid of all your digested food through your mouth, it's not very pleasant, but it's exactly what flatworms and jellyfish have to do.
The flatworm has an extendable stomach with just one opening. And the snag with that is, it can't eat and excrete at the same time. And while some worms stayed flat, others became round. They developed an internal tube--the through gut. In through the mouth, along the digestive tract and out through the anus. This meant worms could feed nonstop and the through gut was such an efficient system that since then every worm has had one.
But bizarrely, some animals today have evolved an entirely different use for their guts. This is a sea cucumber, it doesn't look like much, but when it's attacked by a predator, it does something rather extraordinary. Just holding it can set it off.
"oh,oh ,well here we go. Oh, god, that is foul."
The sea cucumber throws up not only its stomach contents, but its entire intestines. A predator would rather leave it alone, and just eat its entrails. Fortunately the sea cucumber can still live by absorbing nutrients through its skin, and that 's not all.
"Incredibly this guy will grow an entirely new set of guts in just a few weeks."
But throwing up each time when you are threatened is a bit extreme. Other soft-body creatures would need a more practical form of protection to survive.
Around five hundred and seventy million years ago, there was a major breakthrough when life chanced upon a winning formula. The softies turned hard. |
