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The first forefathers of living beings---and that includes you, the human----may have been sea sponges, according to a study by researchers at the Massachusetts Institute of Technology (MIT). The study suggests that sea sponges might have been the first animals on earth.

With genetic analyses, the study showed that sea sponges were the source of a unique molecule found in 640-million-year-old rocks that predated the Cambrian period, when animal life "exploded" on the planet.

"We brought together paleontological and genetic evidence to make a pretty strong case that this really is a molecular fossil of sponges," David Gold, who participated in the research, said in a press release. "This is some of the oldest evidence for animal life."

Some paleontologists surmise that modern animal groups "exploded" quickly in the Cambrian period, but fossils predating their occurrence have cast that belief into doubt. They have raised questions related to the first animals on earth.

Gold and his team probed this issue by studying molecules that have remained in ancient rocks after animal life was washed away.

"There's a feeling that animals should be much older than the Cambrian, because a lot of animals are showing up at the same time, but fossil evidence for animals before that has been contentious," Gold said. "So people are interested in the idea that some of these biomarkers and chemicals, molecules left behind, might help resolve these debates."

While earlier, scientists located the sterol 24-isopropylcholestane, or 24-ipc, in 640-million-year-old rock samples----the earliest evidence of animal life---Gold and his team studied the genomes of about 30 diverse organisms to find out the sterols they produced and the genes that were related with them.

This made the scientists identify one gene, sterol methyltransferase (SMT), that is said to be responsible for creating unique sterols, depending on the number of SMT genes in the organism. They also found that sea sponge and algae species creating 24-ipc have an extra copy of SMT compared to close relatives.

Scientists mapped the gene relationships onto the evolutionary tree, and found that sea sponges evolved an extra SMT copy about 640 million years ago, much earlier than algae. This made them the earliest life form on earth.

"This brings up all these new questions: What did these organisms look like? What was the environment like? And why is there this big gap in the fossil record?" Gold concluded. "This goes to show how much we still don't know about early animal life, how many discoveries there are left, and how useful, when done properly, these molecular fossils can be to help fill in those gaps."

The study was published in the Feb. 24 issue of the Proceedings of the National Academy of Sciences.

YouTube/Massachusetts Institute of Technology