Creationists have loved to talk about “missing links” in the fossil record for almost 150 years as a way of suggesting that evolution couldn’t have happened. Their reasoning is that if we haven’t found a transitional link between two species, then it must not be there to be found.
The thing is that it takes a lot of looking to find some kinds of fossils. So, over the many generations since Alfred Wallace and Charles Darwin came up with their theories of evolution of biological species through natural selection, people have been looking, and filling in those supposed missing links, one by one.
A very early link has just been found, in the form of an ancient chemical that’s found in an animal called a demosponge. These animals exist today, but as a group they’re very ancient: At least 635 million years ancient. That’s the age of rocks within which 24-isopropylcholestane was found. 24-isopropylcholestane is a steroid produced only in living animals – in demosponges.
This is the earliest evidence of animal life on Earth that has ever been found – one link closer to the beginning of the very long chain of animal life, a chain that may never be completely seen, due to its ancient nature, but looks quite full of connections, from what we can see. Follow the chain for long enough, and you’ll see how the demosponges connect to gigantic prehistoric snakes and whales that walked on land.