Humans and mushrooms are surprisingly close relatives on the tree of life. Both belong to a group called Opisthokonta, which means animals and fungi share a common ancestor that lived roughly 1.1 billion years ago. To put that in perspective, your lineage split from fungi hundreds of millions of years *after* it split from plants. You are more closely related to a mushroom than a mushroom is to a daisy.
Why Fungi Are Closer to Animals Than Plants
For centuries, fungi were classified as plants. They grow in soil, they don’t move, and they look vaguely botanical. But at the molecular level, fungi and animals share a defining trait: their ancestors had cells powered by a single rear-facing tail (called a flagellum) used for swimming. This feature groups them together in the same branch of complex life, separate from plants, algae, and other major lineages.
The similarities go deeper than that single ancestral feature. Fungi and animals both digest food externally before absorbing nutrients, rather than making their own energy from sunlight the way plants do. Both store energy as glycogen, a rapidly available sugar molecule. Plants, by contrast, store energy as starch, a more compact, slow-release form suited to organisms that stay in one place and release energy gradually through day-night cycles. Fungal glycogen falls somewhere between the animal and plant versions in structure, with properties that support quick energy release, much more like the animal strategy than the plant one.
Shared Genes Tell the Story
Baker’s yeast, a single-celled fungus, shares about 2,146 genes with humans that trace back to a common origin. Because the human genome has duplicated many genes over evolutionary time, the number of human genes with a yeast counterpart is even higher: roughly 3,940. And these aren’t trivial genes. Over 700 human genes can actually *replace* their yeast equivalents and keep the yeast cell alive and functioning, a remarkable demonstration of how little these core instructions have changed over a billion years of evolution.
Of those replaceable genes, at least 157 are linked to known human diseases. That’s why yeast has become one of the most important tools in medical research. Scientists can study how a gene works in yeast and draw meaningful conclusions about what goes wrong when the same gene mutates in people. And yeast is just one fungal species. When researchers look across the entire fungal kingdom, the number of genes with human counterparts roughly doubles, because different fungal lineages have preserved different sets of ancestral genes.
Cells Built on the Same Blueprint
One of the clearest signs of the relationship between humans and fungi is how their cells are constructed. Both use sterol molecules to maintain the structure of their cell membranes. In animals, that molecule is cholesterol. In fungi, it’s ergosterol. These two molecules are structurally similar enough that they behave almost identically: both stiffen cell membranes, control what passes through, and influence mechanical strength and fluidity in comparable ways. Molecular simulations show that the electrical charge distribution around the business end of each molecule is so similar that researchers can model them with the same parameters.
This cellular resemblance is actually a major problem in medicine. Bacterial infections are relatively straightforward to treat because bacterial cells are built so differently from ours. Antibiotics can target structures that human cells simply don’t have. Fungal cells, though, are eukaryotic, just like ours. They have nuclei, similar internal machinery, and overlapping metabolic pathways. Designing a drug that kills a fungal cell without damaging a human cell is like trying to poison your neighbor’s nearly identical house without affecting your own plumbing. The enzyme pathways that make ergosterol in fungi have close counterparts in human cells that make cholesterol, and mutations in those human counterparts are linked to real diseases. This is why we have far fewer antifungal drugs than antibiotics, and why the ones we do have tend to carry more side effects.
What We Share With Mushrooms but Not With Plants
The list of features that unite fungi and animals, to the exclusion of plants, is longer than most people expect:
- Energy storage: Both use glycogen. Plants use starch.
- Cell walls: Fungal cell walls contain chitin, the same tough sugar polymer found in insect exoskeletons, crab shells, and other invertebrate structures. Plants use cellulose instead. Humans don’t have cell walls at all, but the fact that fungi build theirs from an animal-kingdom molecule is telling.
- Nutrition: Both fungi and animals are heterotrophs, meaning they consume organic matter for energy rather than photosynthesizing.
- Genetic regulatory tools: Fungi and animals share families of gene-control proteins, including the FOX family of regulatory genes, that are not found in plants. These molecular switches help coordinate how cells develop and specialize.
How 1.1 Billion Years of Separation Looks
The best current estimate places the split between animals and fungi at approximately 1.1 billion years ago, with a confidence range stretching from about 1 billion to 1.2 billion years. At that point, the common ancestor was almost certainly a single-celled aquatic organism. It wasn’t a mushroom, and it wasn’t an animal. It was something simpler that carried the genetic toolkit both kingdoms would later build on in radically different directions.
Animals went on to develop nervous systems, muscles, and internal skeletons. Fungi went the opposite route: they lost mobility, grew as networks of thread-like filaments, and became the planet’s most important decomposers. Despite those dramatically different lifestyles, the core molecular machinery stayed remarkably conserved. The proteins that manage basic cell functions, copy DNA, produce energy, and handle stress responses remain recognizably similar across both kingdoms. That billion-year-old inheritance is why a yeast cell can run on a human gene, and why a drug aimed at a fungal infection can sometimes hit human cells too.