While we, as men, occasionally act like Neanderthals (with smaller foreheads). But, you can always blame that on faint traces of Neanderthal DNA. You can’t, however, blame your Neanderthal Y-chromosome as that seems to have gotten lost in the mix, or certainly, over time.

Neanderthal DNA? Yes. Neanderthal Y Chromosome? No

Your dad was not a Neanderthal

The Y-chromosome is solely passed between father and son. If you’re called a Neanderthal at any point in your life, don’t blame it on your father. In a study published today in The American Journal of Human Genetics, an international team led by researchers at the Stanford University School of Medicine have effectively rubbished any opportunity to blame your behavior on the Neanderthal as the study suggests that the Y-chromosome of the Neanderthal has been gone for some time.

The lead offer of the study is PhD, a postdoctoral scholar at Stanford, while the senior author is Carlos Bustamante, PhD, professor of biomedical data science and of genetics at the School of Medicine at the same university.

Using nothing more than data from publicly accessed gene sequencing databases the two, and their colleagues, were the first to ever study the Y-chromosome as it relates to Neanderthals, while there has been work done on sequenced DNA from the fossils of Neanderthal women.

If you have allergies, feel free to blame your Neanderthal ancestors, a number of recent studies have suggested they may have been passed down by your Neanderthal ancestors that also account for about 2.5 to 4% of your present DNA makeup.

While that DNA came from interbreeding between “modern” humans and Neanderthals, it doesn’t appear as if the Neanderthal Y-chromosome made the trip into this inter-specie sexy melting pot as humans began their migration from Africa.

Forever humble, Bustamante explains,”We’ve never observed the Neanderthal Y chromosome DNA in any human sample ever tested. That doesn’t prove it’s totally extinct, but it likely is.”

The guessing game begins

The obvious questions are “why not?” and “how come?”

The Neanderthal’s Y-chromosome exclusion from modern human genes doesn’t make a lot of sense, but as scientists that have some guesses, though they generally use fancier names for guesses.

One possibility is that the Neanderthal Y-chromosome was simply incompatible with other human genes, this has merit given that male to female organ rejection rates are higher than the reverse. It’s also possible that the Neanderthal’s Y-chromosome was just a bit lazy and allowed itself to drift into oblivion, like a unhappily married couple that won’t divorce “for the kids.”

“The functional nature of the mutations we found,” said Bustamante, “suggests to us that Neanderthal Y chromosome sequences may have played a role in barriers to gene flow, but we need to do experiments to demonstrate this and are working to plan these now.”

It’s possible that men have women to thank for this lack of a Neanderthal Y-chromosome. Given that there are “minor histocompatibility antigens,” or H-Y genes in the immune system that finds women rejecting male-to-female organ transplants at a higher rate, it’s quite possible that a woman’s immune system (and uterus) might just say “out” to a male fetus with these H-Y genes. In this case “out” would be a miscarriage, I’m not lacking in sensitivity, just wishing to finish this metaphor. Enough miscarriages would explain the absence of the Neanderthal Y-chromosome.

As William DeVaughn once sang, “Just be thankful for what you got.”