The most exciting thing about biology is discovering who you are related to. My human ancestors are a supremely undistinguished bunch of agricultural labourers. My animal, plant, fungal and protistan relatives are a lot more exciting.
Knowing who your relatives are is useful for serious scientific endeavours like working out how closely you are related to your pet. For example, Romy is more closely related to Coalface (a rabbit) than I am to Gerald (a llama).
It's also possible to work out how closely you are related to your meal. Obviously, I am more related to the cheese I ate for lunch (derived from a cow, a fellow mammal), than to the tuna I ate yesterday. I am less related to the mushrooms I will eat tomorrow, but more closely related to them than I am to the seaweed I ate in a noodle soup the other week. I am probably more closely related to the seaweed than to the broccoli I ate the other day. I am only distantly related to the bacteria in yoghurt, which makes me think that moving onto a a high-bacteria diet is the only way to end all this disgusting cannibalism.
I'd like to show how we are related to everything, but I'll start close to home. Here's a picture of all the mammals (or maybe not, I can't seem to get pictures to stay up). You can read the tree like you would a human family tree, with the branches representing divergence from a common ancestor. The closer we are on the tree, the more closely we are related.
Humans are over with the apes and monkeys in PRIMATES. As you can see, our closest relatives are not clever elephants, graceful antelope, or generous organ-donating pigs, but TREE SHREWS. There is a tree shrew in the Melbourne museum. It looks like a rat. Our next closest cousins are bats and gliding lemurs. Thankfully, primates are only distantly related to the CETACEA (whales and dolphins). You already know how I feel about those guys.