Two Fathers One Egg A new technique for same sex conception for men raises some tricky questions.

What will it take for a same-sex couple—two males or two females—to be able to produce a biological child by combining their genomes in the same way that male-female couples do? Just to be clear, we’re not talking about adopting. Nor do we mean one mate fertilizes a donor egg or is fertilized with donated sperm. Those things have long existed. We mean you take two women or two men and make a baby. 

And they’ve already shown it can be done with two male mice. 

For humans, technologically speaking, it just needs to be translated. To be sure, the success rate might not come out anything close to 100 percent, but neither is the success rate for the currently popular high-tech fertility treatment—in vitro fertilization (IVF) and embryo transfer (ET)—or for that matter, plain old sexual intercourse. But factors outside of science, including ethical, legal, and political considerations will surely come into play.

“It becomes ethically interesting and potentially problematic, because we don’t quite know what the product of this conception will be,” according to David Hoffman, a health care attorney and bioethics assistant professor at Columbia University. How will the personhood and parental rights be defined, for instance?

“We may have to contemplate whether a new set of ethical guard rails are needed.”

While we might assume a priori that a child of two same-sex parents would be considered as much a person as anyone else, Hoffman cautions against such assumptions: “While it may be ethically convenient to adhere to a single notion of personhood, and certainly makes ethical analysis simpler, we may yet conclude that advances in synthesized ovum, just as in acceptance of personhood for artificial intelligence machine beings, require that we refine and adapt our definitions of the rights afforded to human people,” he says.

In terms of its potential utility, a new technique, if eventually scaled up to humans, could expand the arsenal of infertility treatments already available to co-ed couples, but it could also produce a baby from two fathers. That’s because either a male or a female individual can supply the genome of a synthesized ovum (female gamete) that an international team of embryology researchers has learned to produce and to fertilize. 

How it works

Most of the cells in your body, other than sex cells, are somatic cells. They each carry a diploid genome, or two sets of chromosomes. Sex cells, also known as germ cells or gametes, (and more gender specifically, ova and sperm cells) are haploid. This means they have just one set of chromosomes, and that’s what allows genomes of two different parents to blend into the double set of chromosomes that the new baby’s somatic cells will contain.

“It’s natural for an oocyte to haploidize,” Gianpiero Palermo, an embryologist and reproductive endocrinologist at Weill Cornell Medicine in New York City, tells This natural tendency, the ability to transform from diploid to haploid, produces a woman’s natural ova, but it’s also the key to the new technique that Palermo and several other researchers based in New York, Oregon, and South Korea, described in a study published early this year. 

“We are inducing meiosis that normally occurs in an oocyte, but we’re using a somatic cell of an individual as the source of the nucleus,” Palermo explains, before elaborating how his new technique differs from cloning, which also begins with the haploid nucleus of a donated ovum being replaced by the diploid nucleus of a somatic cell from an individual. In cloning, such an individual becomes the sole parent, but not in the new technique. That’s because the new technique avoids efforts that cloning specialists use to override the ovum’s natural tendency to haploidize, meaning to cut a diploid genome in half. Being haploid, like a standard ovum, the synthesized ovum is fertilizable by a sperm cell, and furthermore, being more in tune with what an ovum wants to do, the new technique is also easier than cloning, at least on paper.

“The difficulty [of the new approach] is in pairing the homologs so that the haploidization occurs correctly,” says Palermo, but his team met the challenge, and in doing so, they fertilized a synthesized mouse egg with sperm. This resulted in mice from a father and mother in this case, but the same technique could be attempted with two fathers. The process actually happens all in the same session. They generate the synthesized ovum, fertilize it with a sperm, then let it develop into a blastocyst—which takes around three days in mice—at which point it is injected into the uterus of the surrogate mother, where it implants to begin the pregnancy.

“My sperm recipient would go for it, if proven safe.”

As for transitioning the male-male or female-female reproduction technique to humans, Palermo suggests that might take 10–15 years, at least from the perspective of the technology and the usual challenges of introducing reproductive innovations into clinical practice. That doesn’t account for politics, of course. Some people might abhor what they perceive as an attempt to play God. But there are others who would welcome the technology today if it were ready.

“My sperm recipient would go for it, if proven safe,” says Adam (not his real name), a Wisconsin-based engineer in his early thirties who spoke to, under the condition we keep his identity private. His friend, the sperm recipient, is part of a lesbian couple sharing a pregnancy with her wife to the maximum degree currently possible. She provided the ovum, which was fertilized courtesy of Adam, with the resulting embryo transferred to her wife, who is now carrying the actual pregnancy. To be sure, the generation of offspring from two mothers would involve a process different from the two-father technique of Palermo and colleagues, and a female-female process was carried out by a different team back in 2004. But if the technology for same-sex human conception is actually ready for prime time a decade or two from now, will society be ready? Suffice it to say, we have certainly come a long way over the course of human history.

How we got to this point

Notwithstanding the exponential growth of reproductive technology over the past several decades, humans have been striving for expanded options since pre-industrial times. In fact, reproductive assistance has always been available in one form or another—at least to men—throughout recorded history, by way of a low-tech intervention. If the wife didn’t get pregnant, or didn’t produce a male heir, the husband would replace her, at least in the bedroom. Consider the tales of the patriarchs in the Bible, such as Abraham’s coupling with Hagar to provide the son that his partner Sarah could not, or the reign of King Henry VIII, who started the English Reformation and broke with the Catholic Church just so he could remarry in the hopes of fathering a male heir (even though we now know it’s the man’s gamete that determines the sex of the baby).

By the late 18th century, however, the first reproductive technology was tested —artificial insemination. This was improved by the 20th century by spinning the semen in a centrifuge, removing urine and other fluids while concentrating sperm cells, before injecting them into the woman’s uterus. In vitro fertilization became a reality in 1978. Useful in cases when neither sexual intercourse, nor artificial insemination, nor hormonal treatments are enough to compensate for a couple’s fertility problems, IVF is capable of generating pregnancy in any woman with a uterus, regardless of who donated the male and female gametes.

A light micrograph showing a needle about to inject the DNA of a sperm into a human egg, during the process of in vitro fertilization (IVF). CC Studio / Science Source

The road ahead

Bear in mind that the above summary of the advance of reproductive technologies skips various specialized advances, like mitochondrial motherhood in which there can be two biological mothers, plus a father. The latter was developed to enable fertility in situations of rare abnormalities, but we are focused on the coming same-sex twist on reproductive cloning, given its potential societal issues. In fact, the societal issues are actually more challenging than the technical issues, particularly in the wake of the recent Supreme Court decision on the Dobbs v. Jackson decision that overturned Roe v. Wade this past June, opening up a floodgate of disputes on issues that extend far beyond abortion itself. Some people in states where abortion opponents have control also have objections to IVF, because IVF creates embryos that may not be selected for transfer into a woman’s uterus. Those that are not selected create a surplus of embryos with no clear or morally acceptable reason for existing (as the abortion opponents see it). The practice of injecting multiple embryos to maximize the chances of a successful pregnancy, which may later be “reduced” or removed from the uterus to prevent a multiple pregnancy, is also objectionable to opponents, as is the idea that the excess embryos may be vitrified (cryopreserved in a glass-like state without freezing) for an indefinite span of time.

“Look at Arizona and the case Terrell v. Torres, the fight by a divorced couple over their frozen embryos,” Hoffman suggests. For one thing, the noted case was in Arizona, a state so hostile to reproductive rights that it recently enacted a near complete abortion prohibition written in the year 1901. But then the court said that if the couple can’t agree that one or the other [of the] former spouses should be allowed to implant the embryos, the court would order them to be made available to an adopted couple.” As Hoffman puts it, this case is a “resurrection of the embryo adoption movement.”

With the new technique to generate offspring from two fathers, a surrogate mother will still be needed to carry the pregnancy, but maybe only initially, since another technology, the external artificial womb, is also developing in the wings. As for the two-mother technique, such bi-maternal couples might have to be content to produce only daughters—unless or until further advances enable introduction of a Y chromosome into the gametes in order to produce sons. Might some future space colony, with a limited number of founders, be populated only with females availing themselves of such technology? All of this paints a rapidly evolving picture of reproduction, and with it, society, as we look toward the midpoint of the current century and the decades beyond.

Editor’s note: This article was updated on November 16, 2022 to correct the description of the haploidization techniques in the tenth paragraph.

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