Common evolutionary pasts aren't the only kinds of connections to be found on the Tree of Life. For example, take the archaean microbe called Methanosarcina acetivorans and its relationship with the common rat (Rattus norvegicus).

Potentially separated by billions of years of evolution and countless physical and genetic differences, they still have a few things in common: namely the propensity to thrive in dank, dirty places such as rubbish dumps or sewers. However, the methane-producing microbe has a few more tricks up its sleeve. It's able to survive in the extreme temperatures of deep-sea hydrothermal vents, down oil wells, or even oxygen depleted mud beds at the bottom of the ocean. That's more versatile than even the most street-wise of urban rats.

Believe it or not, we humans are biologically connected to insects, such as the fruit fly (Drosophila melanogaster). This section of the tree shows that at some point in the distant past, humans and fruit flies shared a common ancestor. This ancestor's evolutionary course would have split many times – one of the branches eventually leading to mammals, like us, and another leading to insects, such as mosquitoes (Anopheles gambiae).

Despite the obvious differences between these species, they're all classed as metazoan. Their body shapes eventually develop into a fixed form, they move independently, and they must ingest other organisms for energy. And that is how you're genetically related to a fruit fly.

Some pairs of species are located on completely different sections of the Tree of Life, and yet their existences are almost totally intertwined. This is true in the case of the humans and a type of bacteria called Streptococcus mutans.

You might have never heard of them, but these spherical bacteria live in your mouth. Specifically, S. mutans colonises the surfaces of human teeth and are one of the key causes of tooth decay. To continue thriving in the harsh environment of the oral cavity, the Streptococcus genus has evolved into almost 25 specific species, each equipped to flourish in oral areas. While S. mutans is unlikely to hugely impact your life, some of its relatives are harder to ignore and responsible for the likes of meningitis.