Humans are still evolving… but before toasting to that, know this: Some of the genetic changes may make hangovers worse, a new study finds.

So far, only certain populations have genetic adaptations that make it hard for them to process alcohol, but there's no telling how fast it will spread to other populations, the researchers found.

As for people who already have the adaptation, they may have "reduced tolerance to alcohol in today's environment," study senior investigator Benjamin Voight, an associate professor of genetics at the University of Pennsylvania's Perelman School of Medicine, told Live Science in an email. [7 Ways Alcohol Affects Your Health]

The researchers did the study so they could learn which regions of the human genome have adapted — that is, evolved — over the past tens of thousands of years, Voight said. To investigate, they looked at publicly available data from the 1,000 Genomes Project, a large sequencing venture that's collected the genomes of more than 2,500 individuals of diverse ancestries — representing 26 different populations from four continents, Voight said.

After analyzing the genomes, the researchers found a few genetic sites that showed signs of adaptation.

One of these sites is known as the alcohol dehydrogenase (ADH) gene cluster. Previous research has also this pointed out, the study said.

Alcohol adaptations

When people drink alcohol, their bodies break it down into a toxic intermediary known as acetaldehyde. When acetaldehyde accumulates in the body, it can lead to adverse reactions, including facial flushing, nausea and rapid heartbeat, according to a 2007 report in the journal Alcohol Research Current Reviews.

But acetaldehyde typically doesn't stay in the body for long, because it gets metabolized into something less toxic known as acetate, which can be easily broken down and eliminated from the body.

Some people with East Asian ancestry have a genetic variation that makes it uncomfortable to drink too much alcohol. This variation reduces the function of the gene that converts acetaldehyde into the less toxic acetate, Voight said. This means that acetaldehyde can rapidly accumulate in these individuals, leading to hangover-worthy discomfort.

In other words, people with this genetic variation won't be able to drink too much alcohol without feeling its negative effects soon after. On the upside, people with this adaption might have a lower risk for alcohol dependence, the researchers wrote in the study.

However, not all humans are evolving these genetic changes. So far, it's just been detected in people with West African and East Asian ancestry, the researchers found.

It's not clear whether this adaption is happening to protect people against excessive drinking, Voight noted. Instead, the findings show that the pressures our ancestors experienced in the distant past have influenced the "make-up of our genome in many ways," he said. In turn, these adaptations have "influenced the diversity of traits and the susceptibility to disease that we observe today," Voight said.

Other adaptations

The alcohol-related adaptation wasn't the only finding from the study.

Another involves the glycophorin gene cluster, which is thought to play a role in how humans respond to germs, and in particular, with resistance to malaria. It's challenging to know how to interpret this finding, however. This adaptation could be a response to help humans build resistance against malaria, or it could be a response to another pathogen that was present in historical times, and also happens to fight malaria, Voight said.

The researchers also spotted a genetic sequence in the CT64 gene that early humans likely acquired when they had sex with Neanderthals. This sequence doesn't code for an obvious protein, but is expressed in the male testes, Voight said.

The study was published online Feb. 19 in the journal Nature Ecology and Evolution.

Original article on Live Science.