This article was published in Scientific American’s former blog network and reflects the views of the author, not necessarily those of Scientific American
We owe so much of our rich array of pop-cultural references to the Monty Python troupe's satirical genius. There's the "Dead Parrot" sketch, the Ministry of Silly Walks, the entire Holy Grail film -- Jen-Luc Piquant is particularly fond of the faux-French insults: "I blow my nose at you, English pig dog!" -- and of course, the musical sketch that forms the centerpiece of Monty Python's The Meaning of Life: "Every Sperm is Sacred."
The incomparable Michael Palin plays a poor Catholic man who must sell his 63 children for medical experimentation because he and his wife (played by a cross-dressing Terry Jones) can no longer afford their care and feeding. Asked why they don't, say, practice contraception, he explains this is against Catholic dogma, and breaks into song.
On supporting science journalism
If you're enjoying this article, consider supporting our award-winning journalism by subscribing. By purchasing a subscription you are helping to ensure the future of impactful stories about the discoveries and ideas shaping our world today.
C'mon, you all know the chorus:
Every sperm is sacredEvery sperm is great.
If a sperm is wasted,
God gets quite irate.
There's actually some truth to the sacredness of sperm if you look at its history in various global cultures -- or rather, the sacredness of semen, the fluid which contains the sperm. In ancient China, most gemstones were said to be drops of divine semen that had hardened after fertilizing the earth. For instance, jade was believed to be the dried semen of celestial dragons. (Note to self: never wear jade again.)
In Chi Kung and other forms of Chinese medicine, "jing" is sexual energy, which can also denote "essence" or "spirit." That's why masturbation isn't advised among Chi Kung practitioners: it's a form of energy suicide. They must be Masters of Their Domain. Wikipedia informs me that there is a Chinese proverb that literally equates a single drop of semen to ten drops of blood. So it's better to bleed than masturbate.
In ancient Rome, the orchid was believed to derive from the semen of copulating satyrs, just because its twin bulbs reminded the Romans of testicles. That seems quite rational compared to the Etoro people of Papua New Guinea, who believe that young boys must perform oral acts upon their elders and (ahem) swallow the sperm in order to become sexually mature.
Ah, but today, we are the very model of modern scientific rationalists. Sometimes an orchid is just an pretty flower, and puberty can take its own natural course, thank you very much, with no need for gratuitous rituals involving fellatio. For us, sperm has a predominantly practical purpose of being one-half of the material required for us to reproduce.
And sometimes Nature needs a little help from your friendly laboratory petri dish, i.e., in vitro fertilization (IVF). The science of fertility has made great strides over the few decades, but there's still room for improvement, particularly when it comes to techniques for sorting out the most desirable sperm for fertilization.
Back in 2007, a team of researchers at the University of California, Irvine (UCI), and the University of San Diego (UCSD) presented a new sperm sorting technique at a Frontiers in Optics meeting San Jose, California. They used special cone-shaped lenses called "axicons" which, when combined with a standard lens and a laser, form a ring-shaped focal point, forming an annular trap. It's a well-known technique used in laser machining, and to trap atoms in more fundamental physics research.
The nice thing about the technique is you can build a version of the trap that is "tunable" by adding a couple of extra axicons. Shifting one of those lenses slightly along the optical axis changes the diameter of the ring, making it suitable for biological organisms across a broad range of sizes: not just sperm, but algae, microbes, etc., as well.
And according to team member Bing Shao, "The unique geometrical feature of the annular trap provides a way to confine a sperm in the field of view for an extended period without having to deal with sharp turns or changes in swimming curvature." Because sperm are active, slippery little buggers. It's all about finding the egg with them; they just can't sit back and chill.
You can also adjust the power output of the laser you use to make it ideally suited to sperm sorting. In this application, the trap acts as a kind of "speed bump": slower, weaker sperm moving at energies below the threshold of the laser power will be obstructed, perhaps even redirected, while faster, stronger sperm with energies above the critical power threshold just sail right on by. They proved it by using gorilla sperm as a control in the experiments: gorilla sperm is slower and weaker than human sperm.
The next step was to try the technique using sea urchin sperm -- heck, why not? (Actually, sea urchin sperm turns out to be ideal for investigating the correlation between sperm velocity and fertilization ability, simply because it's much easier to observe the fertilization and subsequent embryonic development.)
The UCSD/UCI group planned to repeat the experiments adding a chemoattractant -- the chemical released from eggs to draw the sperm to the target in the first place -- to the center of the ring; the 2007 results were from experiments using no chemoattractant. It's sufficient to separate faster, stronger sperm from the slower, weaker variety, but adding the chemoattractant would make it possible to also select for a sperm with a higher sensitivity to the chemoattractant -- yet another important variable to what makes a successful sperm.
This could all be good news for couples desiring children (or those engaged in animal husbandry) who are having trouble conceiving, since being able to sort the faster sperm improves chances of conception -- the sperm that gets to the egg first gets to fertilize it. However, there are troubling aspects as well, namely, using the technique to preferentially select for gender, or even specific genetic characteristics.
The former is already possible using a variation of IVF (combining it with pre-implantation genetic diagnosis, or PGD), but sperm sorting has been less reliable. The UCSD/UCI technique could change that. X sperm are heavier and swim more slowly compared to the lighter, faster Y sperm, so the technique could easily be used to sort sperm carrying the gene for a female child from those carrying the gene for a male child. Couples could then choose their child's gender with the same, if not better, accuracy as with IVF-PGD. It's all about having the options.
Speed is oh-so-important for a humble sperm, and not just when it comes to human reproduction. In July, New Scientistreported that how fast sperm travel in any given primate species depends on how promiscuous those species tend to be: the more sexual partners, the more competition, and the faster the sperm feel the need to travel in order to be first to fertilize that all-important ovum. (It seems there is also a theory that rates of female promiscuity in primate species may also determine the size of the male's testicles for a given species, according to this excerpt from the Soma Literary Review.)
Researchers at the University of California, San Diego, led by Jaclyn Nascimento, studied both the speed and force of sperm samples from humans, gorillas, chimpanzees, and rhesus monkeys.
How did they get the sperm? Well, one presumes the human males were simply supplied with the usual plastic cup and lad's mags and given a bit of privacy. The chimps and monkeys were tricked into giving it up via the use of artificial vaginas (apparently they're not too discriminating).
But the gorillas required a bit more finesse: they were trained to supply sperm in exchange for candy with -- and I quote -- "the helping hand of a researcher." Yikes! Yanno, you just can't make this stuff up. And inquiring minds want to know: Which unnamed UCSD researcher got stuck with the thankless task of providing a "hand job" to a very large gorilla? Sounds like an assignment for your least favorite grad student... or a member of the Etoro tribe.
Once the sperm from the various species were collected, the samples were diluted and their movement captured on film, then analyzed via computer to determine the speed of any given sperm. Human sperm clocked in at around 0.2 kilometers per hour. Suffice to say, that's on a par with findings of prior studies, so no surprises there. Sperm from chimps and monkeys -- who apparently will do the horizontal mambo with just about anything -- were regular little speed demons, rocketing ahead at about 0.7 kilometers per hour. As for those sweet, faithfully monogamous gorillas, they had the slowest sperm motility of all, meandering along at a pathetic 0.1 kilometers per hour.
As we've seen, it's not just swimming speed, but swimming force that is critical to a sperm's ultimate success, and Nascimento's team looked at that aspect, too, using "optical tweezers" to hold the sperm in place with laser light. (There's a nice introduction to optical tweezers, courtesy of Stanford University, here. Stanford, of course, can lay claim to Steven Chu, who used the technique in his research involving laser cooling and trapping of atoms, which in turned snagged him the 1997 Nobel Prize in Physics.) The strongest swimmers could break past the barrier and move forward, while the weaker swimmers remained stuck.
And once again, chimp and monkey sperm emerged as the clear winners, swimming with a force of about 50 piconewtons, compared to 5 piconewtons in human sperm, and 2 piconewtons in gorilla sperm. One might be tempted to feel bad for the gorillas, with their lazy, under-performing sperm, but considering the implication -- faster, stronger sperm evolve because a species is promiscuous. The gorillas in the UCSD study can take comfort in the fact that their mates are far less likely to cheat.
An earlier version of this post originally appeared at the Cocktail Party Physics archived blog in August 2007.