Love is in the airI love you. Because you smell different than I do. Not quite Titanic or Casablanca or even Olivia Newton-John in Grease. But smells may be part of the reason why we fall in love with a certain person. At least that is what a new study argues.

We’ve known for awhile that animals find their “true love” partly through smells. One of the things they are sensing is whether the potential mate has a different set of MHC genes.

MHC genes are a big part of our immune system. These genes are used to create the huge number of antibodies that we each make to battle bacteria, viruses, etc. Everyone has a different set of these antibodies.

The more varied your MHC genes are, the more invaders your immune system can recognize and defeat. So two parents with very different MHC genes will have kids with immune systems that can recognize (and so defeat) lots of different kinds of bacteria and viruses. Parents with similar MHC genes will have kids with less varied immune systems. (This is a big reason why inbred animals are so sickly.)

Animals can tell about a potential mate’s MHC genes through smell. And people might be able to do this as well.

Lots of experiments have been done where men or women sniff the sweaty t-shirts of members of the opposite sex to see which t-shirt smells better. If the potential mates are of the same ethnic group, the sniffers tend to prefer mates with very dissimilar MHC genes. If the potential mates were of different ethnic groups, the sniffers preferred mates with somewhat but not wildly dissimilar MHC genes.

The new study looked at a group of 30 European American couples from Utah and 30 Yoruba couples from Nigeria. Thankfully there was no sweat smelling involved. Instead the researchers compared the DNA between the spouses of each couple in many different places throughout their genome.

What they found was that for the Utah couples, the DNA around the MHC genes was much less alike than the DNA almost everywhere else. This did not appear to be the case for the Yoruba couples. This suggests that at least for these 30 couples from Utah, having a very different set of MHC genes may have been part of picking a spouse.

Why the difference between the Utahans and the Yorubans? It is hard to say without more data but one possibility has to do with how much of a role social factors play in picking a spouse in each society. Perhaps the European Americans are freer to choose a mate. If this is the case, then they might be more likely to follow some sort of biological imperative.

Another possibility is that this smell test is only a big deal if the potential mates are all very similar to start with. The Utah couples all had pretty similar DNA to each other to begin with. The Yoruba couples’ DNA was less alike.

Of course, this is a total of 60 couples and so is in no way exhaustive and may be proven wrong tomorrow. But it adds to a growing pile of evidence that suggests how mate selection works at the biological level. And it shows the wide range of things we can learn about ourselves by studying our DNA in great detail. Maybe it even gives perfume companies some ideas too.

You’re as likely to be struck by lightning
as to have a severe reaction to a vaccine.

I was reading an article in Time last week about parents not vaccinating their children. The story was about how this phenomenon is becoming more widespread.

These kinds of stories are weird to me because vaccines are pretty safe. The risk of an adverse side effect is incredibly small. For example, the risk for anaphylaxis from the Hepatitis B Virus vaccination is around 1 in 600,000. This is about the same risk as being struck by lightning (1 in 700,000).

Of course, the article wasn’t talking about known risks. Instead, it was referring to a hypothesized link between vaccines and autism.

People proposed this link when they noticed that cases of autism and the number of vaccinations were rising at the same time. Of course, just because two things happen to occur at the same time, this does not mean they are causally linked. For example, the increase in global temperature is not related to the decrease in the world’s populations of pirates (despite what the Pastafarians say).

So how could an increased number of vaccinations cause an increase in the number of cases of autism? I have seen two ideas put forth. The first is that thimerosal is to blame. The second is that there are so many vaccinations now that we are stressing out the body’s immune system. Most likely neither idea is valid.

Thimerosal is a mercury-based preservative that used to be used in vaccines. Even though there haven’t been any good studies on the effects of thimerosal on brain development, everyone knows mercury is bad for the brain. So the idea behind thimerosal makes some sense.

Back in 2001, vaccine manufacturers decided to eliminate thimerosal from their vaccines. We would predict, then, that cases of autism should go down significantly if thimerosal was linked to autism. They haven’t. In fact, in one California study, cases have continued to climb. So thimerosal is most likely not to blame.

Another point that has been made is that there are so many vaccines now that we are stressing out our bodies’ immune systems. Again, this concern is unfounded.

Vaccines are injections of viral proteins. Our bodies see the proteins and raise antibodies to them. Then when a virus invades, we have antibodies that recognize the virus and target it for destruction.

It is the number of viral proteins that matter in terms of taxing the body’s immune system and not the number of vaccinations. All of the current vaccines put together do not have as many viral proteins as the old smallpox vaccine (150 vs. 200). So the number of vaccines is unlikely to be the issue.

What all of this means is that vaccines are probably not responsible for the significant increase in the number of cases of autism. What is responsible? No one knows for sure.

It may be that the rise just comes from all of us recognizing the symptoms more. Or it could be due to some cause we don’t know about or understand.

What we do know is that vaccines save many lives. I assume no one wants to go back to the early 20th century when polio epidemics swept the country. For example, 2,500 cases of polio ended up at one Los Angeles hospital between May and November of 1934. And in 1952, the U.S. had 21,000 cases of paralytic polio.

We can prevent this sort of thing from happening by making sure everyone is vaccinated. And yet there are people who choose to hide behind the people who take the miniscule risk of getting vaccinated.

Is this a matter of free choice? Should parents be allowed to opt out of vaccinating their children even if it risks society at large?

One idea, I suppose, is to have people who choose not to be vaccinated to sign a waiver saying they accept full responsibility for their actions. In practice this would mean that health insurance and the government would not be responsible for their children’s health care bills if they become ill with one of the diseases they refused to be vaccinated against.

And if your infant, grandma, or immuno-suppressed cousin came down with a disease these folks refused to be vaccinated against, then you could sue the un-vaccinated for damages. The common good isn’t enough to encourage these folks. Perhaps threats to their pocketbook will be.