Deoxyribonucleic acid, or DNA, serves as the universal instruction manual for all known life forms on Earth. This complex molecule carries the blueprint for how an organism develops, functions, and reproduces. Because the fundamental components of DNA are the same across all species, all life is connected through a shared genetic history. This shared foundation leads to a surprising question: how much of our genetic code is similar to something seemingly as distant as a tree? Exploring this relationship reveals deep evolutionary connections that link humanity to the entire plant kingdom.
Measuring Genetic Similarity to Trees
Determining a single percentage of shared DNA between humans and trees is complex, as the number depends entirely on the method of comparison. When scientists measure genetic similarity between distantly related organisms, they focus on comparing the functional genes that code for proteins, rather than the entire length of the genome.
Using this comparison method, humans share approximately 15% to 25% of their functional genes with common plant species. Comparative genomic studies frequently use the model plant Arabidopsis thaliana to represent the plant kingdom. Analysis shows that humans and Arabidopsis share about 18.7% of their protein-coding genes, or orthologs, which are genes derived from a common ancestral gene. This means that nearly one-fifth of human genes are recognizably similar to those found in a plant.
The shared genetic material often includes genes responsible for fundamental cellular housekeeping tasks. These genes have sequences similar enough to be clearly identified as serving the same purpose in both a human cell and a plant cell. The percentage of shared functional genes highlights a degree of conservation, despite the overall DNA sequence length and total gene count differing dramatically between humans and trees.
The Evolutionary Roots of Shared DNA
The reason humans possess shared genetic material with trees lies in the concept of a single origin of life on Earth. All life evolved from a common ancestor, often referred to as the Last Universal Common Ancestor (LUCA), which existed billions of years ago. Both plants and animals are descendants of this ancient organism, which possessed the initial set of instructions for basic survival.
The genes conserved across this vast evolutionary distance code for processes necessary for any eukaryotic cell to live. These highly conserved genes handle basic energy production, cell division, DNA replication, and protein synthesis. For example, the genes involved in cellular respiration, the process that converts energy from food, are remarkably similar in both humans and plants, despite plants also performing photosynthesis.
Any significant change to these fundamental housekeeping genes over the course of evolution would have been lethal. Because these functions are basic and universally necessary, the genetic codes governing them have remained largely unchanged for more than a billion years, maintaining their sequence similarity. This evolutionary pressure to keep the basic machinery intact explains why a tree and a human still possess similar genetic instructions for certain core biological functions.
How Tree Similarity Compares to Other Organisms
To put the 15% to 25% genetic similarity with trees into context, it is helpful to compare it with the shared DNA percentages of other organisms. As expected, genetic similarity is highest among species that share a more recent common ancestor with humans. For example, humans share approximately 96% to 98.7% of their DNA with chimpanzees, our closest living relatives.
Moving further down the evolutionary tree, humans still share a large portion of their DNA with other organisms:
- About 85% with mice.
- Around 60% with fruit flies.
- An estimated 50% to 60% of their genetic material with a banana.
- Roughly 30% to 40% of orthologous genes with fungi, such as yeast.
The relatively low 15% to 25% shared functional gene percentage with trees illustrates the vast evolutionary time separating the animal and plant kingdoms. This significant distance means that while the core cellular functions remain conserved, the genetic instructions for unique features—such as circulatory systems, nervous systems, leaves, and bark—are entirely different. The comparison highlights that the small fraction of shared genes represents an ancient, common heritage for nearly all complex life.