Some 450 million years ago, sharks and humans shared a common ancestor, making sharks our distant cousins.
And according to recent research, this kinship is evident in our DNA, as at least one shark species possesses several genes that are nearly identical to those in humans.
Researchers at the Institute of Molecular and Cell Biology in Singapore have found that that the elephant shark's genome is very similar to humans and many things common with it than the teleost (bony skeleton) fishes, which are closer to humans on the evolutionary tree.
"This was a surprising finding, since teleost fish and humans are more closely related than the elephant shark is to humans," says lead author Associate Professor Byrappa Venkatesh.
Venkatesh and his team determined that sets of genes on chromosomes, as well as genetic sequences are highly similar in the elephant shark and human genomes.
They also compared with other animals like puffer fish, chickens, mice and dogs to see whether they resemble human genomes.
They published their findings in the journal PLoS Biology.
The researchers identified 154 genes in humans that matches comparably with mice, dogs and elephant sharks. The mice and dogs have been found similar to human genome before, because mammals exhibit similar characteristics. But to see Tiger Shark resembling humans is a big surprise for the researchers.
The study showed that sharks and humans do share certain physiological and biochemical processes. One of them is sexual process.
"A common feature between the elephant sharks, other sharks and humans is that in all, the fertilization occurs internally, whereas in teleost fishes, fertilization occurs externally," Venkatesh says.
Many genes compare similarly between sharks and humans involved in the production of sperm. Both species produce sperm that appears to have receptors on the tip that allow fusing with a female egg.
Other bony fishes do no have such receptors. Their sperm enter eggs via a pore called micropyle, which both sharks and humans lack.
Besides this similarity the researchers also found that the shark and the human immune systems are similar. Sharks have all four types of blood cells found in mammals.
Sean Van Sommeran, executive director of the Pelagic Shark Research Foundation in California was not surprised about the shark-human genes similarities.
"Sharks copulate like mammals and females give birth to live young, so sharks do have features in common with mammals. It makes sense that these would show up in the genome."
But he should give credit to the researchers for finding this and making the results public.
Venkatesh will study further about the elephant shark genome, which he says are easy to study and relatively small, wants to see how the immune system develops will help understand the human’s immune system.
Since sharks are the oldest living jawed creatures with a backbone, studies on them may even uncover how humans and other mammals evolved.
It is interesting to find how sharks and humans are related and have many things in common.