In the 1920s, Joseph Stalin sent researchers to Africa as a secret program to create a hybrid race of ‘man-apes. These man-apes would have been a formidable force that featured a man’s intelligence with the strength and speed of a chimpanzee. The program failed despite dozens of attempts to impregnate apes with human sperm.
Species are defined as animals that can interbreed and produce fertile offspring. For example, a giraffe can not breed with an elephant. But a bulldog, chihuahua, and a wolf can all breed with each other. There can be considerable changes in how animals look so that their genetics are similar enough that babies are possible. When two different species of animals have a baby together, it’s known as a hybrid. So can humans breed with other animals?
Many different hybrids are possible. There are tons of other animals that can be hybrids. Some have fertile offspring, and some can. There is no exact defined line between one species and another. It’s more of a gradient, and that’s because animals go through natural selection even among different populations within the same species. The web of human evolution is one of the most exciting yet confusing areas in all evolutionary biology.
Can humans breed with any other animals?
Humans have 23 pairs of chromosomes. That’s a total of 46, and 22 pairs look the same in the male and female and are called autosomes. The 23rd pair is the sex chromosome which differs between males and females. Males have one X and Y chromosomes, and females have 2X chromosomes.
Reproductive isolation is an evolutionary mechanism. It is behaviors and physiological processes by which a species cannot mate outside of its species. It is critical for speciation or how populations become distinct species.
- Scientists have identified various factors that make it impossible to interbreed with animals. They separated them into two groups: pre and post-zygotic reproductive isolating mechanisms.
Pre-zygotic: Pre-zygotic reproductive isolating mechanisms are all the things that make it physically impossible to attempt to breed in the first place. Geographic isolation is one of these mechanisms. After too long, one species has physically changed so much that it simply does not find another species sexually attractive. There is no inclination for either to attempt to mate.
Other mechanisms include physical attributes such as incompatible genitalia, psychological factors such as a prey/predator relationship, and sperm motility. One species’ sperm may not be capable of navigating the reproductive tract.
Post-zygotic: post-zygotic reproductive isolating mechanisms are those factors that make it impossible for a hybrid fetus to grow into a reproductive adult. So if two animals of entirely different species managed to mate, they could still produce no viable offspring.
The farther apart two animals are genetic, the less likely they will mate successfully. We’ve been too far removed from apes for genetics to match up with humans. Humans are diverging from apes as late as 7 million years ago. There’s not enough common ground any more for viable offspring.
While there are several factors, and scientists still don’t fully understand them, the biggest factor is DNA. Human and animal DNA doesn’t match up to produce anything worthwhile. As the body’s ‘operating system,’ DNA tells every cell in the body what and how to become it. One cell might become muscle tissue, while another becomes a red blood cell.
- DNA is the internal instruction manual, and things must line up precisely for DNA to do its job correctly. However, when scientists attempt to mix human and animal DNA, the instructions don’t match.
Imagine you have one set of instructions for building a boat and another for building a skyscraper. Mixing them up together results in one document that makes no sense. It is not suitable for creating either a boat or a skyscraper. Recent evidence in DNA shows that humans have interbred with other species, such as Neanderthals, who make up a few percentage points of everyone’s DNA.
So why are Neanderthals and not Stalin’s gorillas and chimpanzees? Humans and Neanderthals looked very physically similar, so some attraction was inevitable. Human physical bodies are also appropriately aligned, being a near mirror copy of each other.
Those post-zygotic reproductive isolating mechanisms failed to affect reproductive tracts nearly identically upon successful mating. So human sperm could easily navigate the reproductive system of a Neanderthal female and vice-versa. DNA was also closely similar in that the instructions ‘made sense’ and resulted in viable offspring.
What would happen if a human mated with an animal?
The branches of life spread out in every direction as life finds its way into every niche imaginable. A new species arise in a process called speciation. It’s when something happens to separate it from all that came before, like a unique trait or geological isolation. Naturalists like Charles Darwin used to tell species apart from the old-fashioned way.
If two animals can make a baby that lives and later make its baby, then those animals are the same species. It is basically what the Biological Species Concept (BSC) says. Biologist Ernst Mayr introduced this concept in the mid-20th century.
- Species are groups of interbreeding natural populations reproductively isolated from other such groups.
Different species evolved traits in similar environments, like Fossas and cats, which cannot reproduce. Or different species might be closely related and look alike but can’t produce fertile offspring like horses and donkeys. They can produce a hybrid called a mule, but they’re sterile. But even on a more acceptable level, sometimes scientists get surprised and find that different species might not be so other.
A study published in the journal Biology Letters found that different species of Rock-Wallabys were swapping DNA! Six different rock wallaby species were considered separate species because of how their genetic material package would stop an offspring from being fertile. But upon genetic analysis, the researchers found gene flow between the species, suggesting something else was going on, forcing them to rethink their evolution.
This finding suggests that these animals were getting it on, making babies that could make more babies. The rock wallabies might not be “reproductively isolated.” It means they were more like a single species than previously thought. So if a human mated with an animal, nothing would happen, and no fertilization will occur?
Like in the case of these rock wallabies, scientists could see a species’ history written in its DNA. By comparing the DNA of different animals, scientists can see how they’re related or not. This was a massive advance in the field of taxonomy.
According to a study published in the Journal of Biogeography, we share more physical features with orangutans, like the beards of men and similar shoulder blades. So it can help us learn about the rest of the world, but taxonomy helps us find a place in the animal kingdom.
Lombard, M; Jakobsson. “Southern African ancient genomes estimate modern human divergence to 350,000 to 260,000 years ago”.
Woodward, Aylin. “A handful of recent discoveries have shattered anthropologists’ picture of where humans came from, and when.”
“Crossbreeding Beef Cattle – Home – Virginia Cooperative Extension.”
Rogers Ackermann, Rebecca; Mackay, Alex; Arnold, Michael “The Hybrid Origin of “Modern” Humans.” Evolutionary Biology.