Mammal embryos can be manipulated at a very early stage, then implanted into the stationary womb of a surrogate parent using in vitro fertilization techniques. “You can’t do that with a bird,” says Preston. Birds begin to develop the protective eggshell and nutritious yolk at the same as the embryo itself develops, all while inside the bird mother.
Other researchers, including McGrew, have developed painstaking ways of creating genetically modified chickens by isolating, growing and manipulating special stem cells called primordial germ cells—precursors to sperm and egg cells—in laboratory cultures, injecting them into birds to alter their reproductive organs to carry sperm or egg cells from transgenic birds, then mating two such birds together to create an egg that births a new genetically altered bird with different traits.
The same process has not succeeded for most other birds, and it has never been tried with DNA from extinct species. “It’s a very laborious process, and the success rate is low,” says Cheng.
A scientist at Colossal Biosciences checks on the newborn chick.
Colossal Biosciences
Last fall, Colossal said it had achieved the first step, culturing primordial germ cells from a common pigeon, also known as the rock dove, which is genetically similar to the Nicobar pigeon that Colossal says could be a surrogate for the dodo. The company says it had not yet selected a surrogate egg-producer for the giant moa, but that the emu and tinamou are possible candidates. A moa would eventually outgrow any surrogate egg, so Colossal intends to transfer the developing embryo to their artificial egg system at some point in the process.
“I think they still have a long way to go,” says Cheng.