When comparing the DNA of different animals, scientists look for similarities and differences that indicate how closely or distantly related they are. The more similarities two animals share in their DNA, the more closely they are related. Based on genetic studies, our closest living relatives in the animal kingdom are chimpanzees and bonobos.
Why do scientists compare animal DNA?
Comparing the DNA sequences of different organisms is a powerful way for scientists to learn about evolution. DNA carries the instructions for building all living things. Tiny changes that accumulate in DNA over time lead to the diversity of life we see today. By studying similarities and differences in DNA, scientists can better understand the evolutionary relationships between species. This helps them draw an evolutionary “family tree” showing how different organisms are related.
What types of DNA do scientists compare?
Scientists mostly look at chromosomal DNA, the DNA found packaged into chromosomes inside the nucleus of each cell. They especially focus on DNA that codes for genes. However, they may also study mitochondrial DNA, which is a small amount of DNA located outside the nucleus in cellular energy-producing structures called mitochondria.
Both chromosomal and mitochondrial DNA contain genetic instructions, but they change at different rates. Mitochondrial DNA tends to change faster over time. Comparing both types can provide insights into evolutionary relationships over different timespans.
How similar is human and chimpanzee DNA?
Humans and chimpanzees share a remarkably high amount of their DNA sequence. After analyzing the chimpanzee genome, scientists estimate that human and chimpanzee DNA is about 96-98% identical. That 2-4% difference might not seem like much, but it accounts for some striking differences between humans and chimps in terms of anatomy, behavior, intellect, and other traits.
Even DNA that codes for the same trait, like vision or limbs, can differ slightly between humans and chimps. These small changes alter the proteins built from each gene, affecting how the trait develops. Over the 6-7 million years since the human and chimpanzee evolutionary lines diverged, many small changes accumulated.
Key genetic similarities and differences
Despite the genetic similarities, some regions of human and chimp genomes show major differences:
- Chromosome 2: Humans have just 23 pairs of chromosomes, while chimpanzees have 24. Human chromosome 2 formed through the fusion of two smaller chromosomes still distinct in chimps.
- Y chromosome: Only 30% of the human and chimp Y chromosomes match up, indicating faster evolutionary change.
- Gene regulation: Changes in when and where genes turn on likely underlies many human-chimp differences.
- Copy number differences: ~80 genes lost in humans, ~80 gained or amplified compared to chimps.
Do any other animals share similar DNA with humans?
After chimpanzees and bonobos, the next closest DNA similarities to humans have been found in other great apes – gorillas and orangutans. All great apes evolved from a common ape ancestor around 10-20 million years ago. Beyond the great apes, the next closest DNA likenesses have been found in gibbons, followed by Old World monkeys like baboons and macaques.
Here is a table showing approximate DNA similarity percentages between humans and other animals, from closest to most distant genetic relationships:
| Animal | DNA similarity to humans |
|---|---|
| Chimpanzee | 96-98% |
| Bonobo | 96-98% |
| Gorilla | 95-96% |
| Orangutan | 94-96% |
| Gibbon | 91-95% |
| Old World Monkey | 90-93% |
| Mouse Lemur | 82-90% |
| Dog | 84% |
| Mouse | 75% |
| Fruit Fly | 60% |
As shown, the genetic similarity drops off sharply after the great apes. Still, many animals share a reasonable amount of DNA with humans, reflecting our shared evolutionary origins.
Why are chimpanzees our closest DNA relatives?
Humans and chimpanzees belong to the same taxonomic group known as hominins. “Hominin” refers to the human branch that diverged from a common ancestor with chimpanzees roughly 6-7 million years ago in Africa. Since then, chimpanzee and human ancestors evolved along separate paths but remained more closely related to each other than other apes.
Several key factors contributed to chimps remaining our nearest evolutionary cousins:
- Recent divergence – Chimp lineages split off most recently from human ancestors compared to other apes.
- Shared ancestry – Both evolved from the same ancient hominin ancestors.
- Common environment – Both continued inhabiting similar African tropical forest environments.
- Reproductive separation – Populations remained isolated reproductively which sped genetic divergence.
- Slow mutation rate – Critical DNA preserved more than fast-changing DNA.
In essence, humans and chimps trace back to a relatively recent common ancestor. They continued evolving similar traits adapted for a shared environment even as they became reproductively isolated new species.
How did scientists sequence chimpanzee DNA?
Advanced DNA sequencing technology enabled scientists to read the precise order of nucleotides within chimpanzee DNA. Key innovations included:
- Automated Sanger sequencing (1977) – Allowed short DNA fragments to be rapidly sequenced.
- Polymerase chain reaction PCR (1985) – Enabled exponential amplification of small DNA samples to provide enough material for sequencing.
- Shotgun sequencing (1990s) – Entire genomes sequenced by breaking DNA into small, randomly overlapping fragments.
- High-throughput sequencing (2000s) – Massively parallel techniques increased speed of sequencing exponentially.
These advances enabled the chimpanzee genome project, launched in 2003. A first rough draft was completed by 2005. Scientists could then directly compare the chimp and human genomes, discovering their remarkable similarity.
Conclusion
In summary, through comparative genetic analysis, scientists discovered humans share about 96-98% of our DNA sequence with chimpanzees and bonobos. This makes them our closest living relatives in the animal kingdom. Slight DNA differences accumulated in the 6-7 million years since humans diverged from a common ancestor with chimpanzees. But major similarities remain due to our relatively recent shared ancestry. Understanding the small genetic changes specific to each lineage provides insights into human evolution and what makes humans biologically unique.