Science Matters

Woolly Mammoths, fat dogs & living fossils

Boyce Rensberger

(5/2024) There have been some cool developments in science that I think readers will find interesting, but they don’t require all the space this column normally occupies. So here is the first of what may become an occasional list of briefs based on recent scientific reports.

Quite by accident, all three of these items deal with genetics. That’s the area of science that I know best and follow most closely. In the future I’ll try to range farther afield.

If you like these short items, let me know by writing to me at the address at the end. I’ll answer everyone who writes.

Bringing Back The Woolly Mammoth

A biotech company says it has taken a major step toward its stated goal of recreating the woolly mammoth. The American outfit, modestly called Colossal Biosciences, labels its process "de-extinction."

As the company puts it on its website, rather breathlessly, "we endeavor to jumpstart nature’s ancestral heartbeat. To see the woolly mammoth thunder upon the tundra once again."

What the scientists say they did was to take skin cells from a living Asian elephant, grow them in a dish and then chemically treat the cells to make them lose their specialized functions. The treatment includes things like removing attached molecules that block some genes from working. This resets the genome to a version of a stem cell. In principle, these cells are typical of those in a very early embryo, capable of multiplying and diversifying into the many specialized cells of a whole organism.

The company says it now will re-engineer certain genes that differ between mammoth and modern elephant to be like those in tissues of real woolly mammoths found frozen in Arctic ice. The genome of these extinct beasts is thought to be fairly well known. This kind of detailed genetic modification is possible using a relatively new technique abbreviated CRISPR. Then nuclei of those modified cells would be injected into an egg from a living elephant. (The egg’s original nucleus would first be removed.) That egg would then be implanted in the uterus of a living surrogate mother elephant.

Don’t order your tickets yet for Pleistocene Park. Many difficult steps lie ahead, but some quite reputable scientists are affiliated with the company, and I wouldn’t discount the promises they make. By the way, if you want to learn more about this and if you enjoy highly developed (maybe even too developed) websites, I recommend the company’s at colossal.com. Use your device with the biggest screen.

Overweight Dogs May Feel They Are Starving

Labrador retrievers and flat-coated retrievers are two of the most obesity prone dog breeds. Many beg for more food even after finishing a meal.

Now a team of scientists from the University of Cambridge in England have found what appears to be the cause. Significant percentages of these breeds are born with two genetic mutations that prevent their gut from sending the normal chemical signals—a specific hormone plus an endorphin (the brain’s natural opioid)—that tell the brain they are full and happy. So, these dogs just keep eating unless their owners are strict about what’s for dinner. One of the mutations also produces a hormone that regulates the body’s energy expenditure. Dogs with that genotype are less energetic, slower in metabolism.

In their sample of dogs, all healthy pets, they found these mutated genes in 12 percent of Labs and 60 percent of flat-coats.

The researchers speculate that these mutations originated at some time in the breeds’ past as ways to cope with food scarcity—slow down but keep gobbling when food is available.

"To maintain a healthy body weight," the researchers write in their report in the journal Science Advances, "owners of affected dogs must restrict food intake to below that which would maintain a healthy body weight in wild-type dogs because of their lower energy expenditure."

The scientists speculate that similar mechanisms may operate in people.

How Living Fossils Resist Evolution

Charles Darwin coined the term "living fossil" to refer to species that appear not to have changed in many millions of years. These include horseshoe crabs, sturgeons, and a few others.

Now comes a study of another living fossil, the gar fish, that finds these animals have scarcely mutated their genes in more than 100 million years. The scientists think the reason is that these species have amazingly effective DNA repair mechanisms.

In almost all other species, if a mutation arises, there is a process that either repairs the damage or causes the cell to die before it can give rise to a new individual or to a tumor. All cells, including those in human beings, have DNA repair mechanisms. That’s because our DNA is being damaged thousands of times each day. Damage is typically from such things as natural radiation, reactive forms of oxygen, chemical carcinogens, sunlight, and simple mistakes in the mechanisms that replicate our genes to carry out cell division.

There are several different repair mechanisms. Basically, they involve molecular machines in all our cells that literally crawl along each DNA double helix, "looking" for signs of damage. If they find a problem, they either repair it or simply block or delete the errant sequence. Or they may trigger a process by which cells commit suicide. The loss of one wayward cell is no big deal.

Now back to the gar and a study published in the current issue of Evolution. There are two different species of gar that have been identified in the fossil record, both of which survive today. They have been separated evolutionarily for more than 100 million years. These two species of Jurassic gars look nearly identical to their descendants living today.

In places where both live, it has been found that they can interbreed and produce fertile offspring. That’s the classic evidence that different species don’t have significant genetic differences. In fact, by one traditional definition, that means they could be considered the same species.

After comparing sequences of DNA from the same genes in many other species—it turns out that the rate of genetic change in gars is anywhere from half as fast as in other species to 1000 times slower.

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