Answer:
A universal common ancestor (UCA).
Step-by-step explanation:
According to Darwin, all life on Earth evolved from a universal common ancestor; that is, the very first organism on Earth. If you pick any living plant or animal on Earth and trace its lineage back far enough, billions of years ago, you will eventually find the UCA. Every species on Earth is united to every other species through their connection with the UCA.
The UCA itself was probably a single-celled organism of some kind and died about 4.1 billion years ago. But through it, every species, be it human, dog, tree, or mushroom, shares this one ancestor with everyone else.
Species also have what's called a lowest common ancestor with each other, much more recent than the UCA. For example, the LCA between humans and chimpanzees probably lived and died around 4 million years ago.