Here we see a happy, typical family of sea monkeys. Note the red bow and plump lips that indicate the female of the species, and the tall body and protective stance of the male. I assume that the father’s well-placed tail blocks some other clues to his identity. The parallels between the sea monkeys and the human family (see inset) are uncanny and surely nothing more than a coincidence.

The real life of sea monkeys (brine shrimp, or Artemia) is a pretty far cry from Ozzie and Harriet. Sea monkeys don’t live in families, for one thing. And in a lot of populations, the females have no need for males. Their eggs can develop into healthy embryos–and, eventually, adults–without the need of sperm. You can take that picture of sea monkeys and wipe Dad out.

From an evolutionary perspective, this father-free way of life has a lot going for it. Let’s say you’ve got a sexual pair of male and female shrimp in one tank, and two asexual females in the other. Let them breed for a while. Sexual species typically produce a roughly even ratio of sons and daughters. So only half of the sexual population can produce eggs, while every individual in the asexual one can. It won’t be long before the asexual population is far bigger than the sexual one. Out in the wild, this proliferation should mean that the genes for male-free reproduction should quickly dominate populations. Down with sex, in other words.

But this has only occurred in only about one in every ten thousand species of animals. Sex must have a powerful advantage that overcomes its disadvantage–what the late biologist John Maynard Smith dubbed the two-fold cost of sex.

Scientists have given this question a lot of thought, and they’ve come up with some possible answers that they’ve been testing in recent years. Maybe sex lets adaptations evolve faster, because mothers and fathers can combine genes into new combinations. Defenses against ever-evolving parasites might be especially important. There may be different explanations for different cases. Very often, when an asexual lineage emerges, it gains an extra set of chromosomes. That’s a lot of extra DNA to build when a cell divides–which requires a lot of phosphorus and other ingredients. Perhaps that’s a cost too great to balance the advantage of giving up fathers.

Or perhaps the rarity of asexual animals is the result of evolution playing out not in short-term competitions, but over vast stretches of time. Populations of sexual animals may be less prone to going extinct because they can adapt to more niches.

To better understand the evolution of sex, a number of biologists are looking to the exceptions to the rule. If the advantages of sex overwhelm its costs for 9,999 species out of every 10,000, then why is the opposite true in the remaining one? One lineage of microscopic animals called bdelloid rotifers has been asexual for 80 million years. Cornell scientists have suggested that they have remained asexual because they’ve found a way to resist parasites that’s as good as sex–by drying up and blowing away from their pathogens.

But there are other puzzles to the evolution of sex. And one involves sea monkeys. In a paper appearing in the Journal of Evolutionary Biology, Marta Maccari of the University of Hull and her colleagues describe a massive survey of brine shrimp from across Europe and Asia. They reared cysts from dozens of populations and closely examined the offspring over the course of two generations. The females in these populations can reproduce on their own. And yet in most of the populations they studied, they discovered a few males.

The males were exceedingly rare–around one in thousand in many cases, and around one in a hundred in a few. And yet they were healthy and fertile. The males couldn’t mate with females of their own population, but they readily had sex with other species. What’s more, their hybrid offspring were healthy and fertile, too.

If asexual animal species are rare, species with asexual females and rare males are even more rare. Only a few other examples have turned up, such as certain populations of snails in New Zealand. Maccari and her colleagues don’t think there’s a clear answer to why these rare males exist. But there are a few plausible possibilities.

Maybe it’s just a fluke. It’s possible, for example, that as eggs develop, a few accidentally lose a chromosome, altering their sex. Sons, in other words, are birth defects.

It’s also possible that some of the asexual brine shrimp have mutations that lead sometimes to males, and they pass their mutated genes down to their offspring. In her study on New Zealand snails last year, Maurine Neiman of the University of Iowa and her colleagues found, surprisingly, that producing a few sons that can’t mate with any females of your species doesn’t put asexual animals at a major disadvantage.

On the other hand, maybe rare males are a side-effect of brine shrimp biology. One way for females to reproduce is to combine two eggs, joining together their chromosomes into a full set. This process can produce lots of different combinations of the shrimp’s DNA, and that variation may help them adapt to the changing environment. Sometimes, though, those combinations may produce a fertile son.

The most interesting possibility Maccari and her colleagues raise is that the rare males are a way for the genes for asexuality to spread themselves. The males can’t mate with their own species, but they can interbreed with others. They may then introduce genes for asexual reproduction into the species, causing them to turn male-free. For brine shrimp, in other words, fathers may be a way of getting rid of fathers. I have no idea how you’d paint that on a box of sea monkeys, but I’d be curious to see someone try.

For this week’s “Matter” column, I write about the bees buzzing from flower to flower this summer. In particular, I take a look at the bees that pollinate 20,000 species of plants–including crops like tomatoes and potatoes–with some amazing acoustics. They vibrate hundreds of times a second to shake pollen loose from special tubes in the flowers.

That’s why you can use a tuning fork to coax some flowers to release a cloud of pollen, as this video from Anne Leonard of the University of Nevada, Reno, illustrates. Bees, in other words, are living tuning forks.

As I continue to catch up from a week’s vacation, I realize that I neglected to point Loom readers to last week’s “Matter” column in the New York Times. It’s a fun one: a look at the species with the fewest known genes in its genome–just 120. Which raises the questions, just how low can you go? Is there some minimal essence of life? The answer is not what you might think. And it involves living inside a mealybug.

Andrew Howley over at National Geographic News Watch shares my fascination with such “Whoa…” questions, and so we exchanged some further thoughts about what it means to be alive. You can read his conversation with me here.

If not for a virus, none of us would ever be born.

In 2000, a team of Boston scientists discovered a peculiar gene in the human genome. It encoded a protein made only by cells in the placenta. They called it syncytin.

The cells that made syncytin were located only where the placenta made contact with the uterus. They fuse together to create a single cellular layer, called the syncytiotrophoblast, which is essential to a fetus for drawing nutrients from its mother. The scientists discovered that in order to fuse together, the cells must first make syncytin.

What made syncytin peculiar was that it was not a human gene. It bore all the hallmarks of a gene from a virus.

Continue reading “Mammals Made By Viruses” →

[Originally published November 30, 2009, updated March 29, 2020]

One of the fundamental challenges of writing about science is choosing the right words. Science is full of jargon, which works well enough for specialists talking with one another. But if you want to share science with everyone else, jargon is toxic, alienating potential readers. Using jargon also becomes a crutch; a writer comes to depend on magical words rather than trying to explain deep concepts. Beyond jargon, writers should also avoid unnecessarily formal language, choosing visceral, potent language instead.

As a teacher, I flag words in my students’ work and encourage them to try again, to strive to do better. (So should all writers.) Over the years, I’ve collected them here. Putting a word on this list doesn’t imply that no one should ever use it. I am not teaching people how to write scientific papers. What I mean is that anyone who wants to learn how to write about science–and to be read by people who aren’t being paid to read–should work hard to learn how to explain science in plain yet elegant English–not by relying on scientific jargon, code-words, deadening euphemisms, or meaningless cliches.

Access (verb)

And/or (Logic gates do not belong in prose)

Anomalous

Anthropogenic

Breakthrough (unless you are covering Principia Mathematica)

Captive observation

Clinical setting

Community ecology (this ban does not extend to the subject of community ecology)

Component

Context

Cracked the code (especially when it comes to sequencing DNA. DNA is not the same thing as the genetic code)

Demographic leveling

Elicit

Elucidate

et al

Facilitate

Food source (when just “food” will do)

Forcings

“Further research is needed” (This phrase may be mandatory at the end of science papers, but it’s meaningless. Has any scientist ever declared further research unnecessary?)

Holy Grail

Immunocompromised

Impact (as a verb. Impacted is fine you’re talking about teeth or bowels.)

Implement (especially as a verb. Launch? Put into practice?)

In (when used in phrases like “experiments in mouse“)

In vitro (Don’t assume a Latin phrase for “in glass” means anything to a non-scientist.)

In vivo

Incredibly

Informed (people can be informed. As for “The discussion was informed…”? Ack.)

Infrastructure (Whenever possible, make readers see what you’re writing about. “Infrastructure” makes me think of a dull white paper, when I could be seeing bridges, highways, dams, and the other biggest creations of our species.)

Insult (referring to an injury)

Interaction

Interdisciplinary (The fact that a project can be characterized as “interdisciplinary” is only interesting in a grant application. But that project itself may be extremely cool. Convey to readers that coolness; don’t deploy funding labels.)

Interface (especially as a verb)

Intermediate host

Interested in (as in, “Dr. Frankenstein is interested in tissue regeneration.” Transforms passion and excitement into a boring parlor game)

It has been shown (Who showed it? How? The kinds of questions that the passive voice can never answer.)

Linked to X (where X=Alzheimer’s, autism, cancer, or any heavily funded area of research. “Linked” tells the reader nearly nothing.]

Literally (even if it’s used accurately, the word is generally useless)

Marine environment

Material properties

Mechanism

Methodology

Miracle (or miracle cure)

Missing link (don’t get me started…)

Mitigation

Modulate

Molecular systematists

Morphology

Multiple (as in many? Then just use many)

Musty (when referring to museum collections, unless those collections are in fact in an attic with holes in the roof through which rain steadily falls)

Non-marine environment

Novel (the adjective is banned. The noun, as in War and Peace, is fine.)

Optimum

Orthogonal

Paradigm shift (Thomas Kuhn only had a few things in mind when he coined this phrase: http://bit.ly/1oKwigs Don’t use it for just any slight shift in scientific understanding.)

Parameter (also, parameterize)

Pathogenicity

Phylogenetics

Predation

Predator-Prey Relationship

Processes

Proxies

Reagent

Recently (when you actually mean “ten years ago”)

Recruit, recruitment (unless you’re writing about the Army)

Regime (unless you’re referring to Mobutu in Zaire)

Robust (as in, robust data. But robust wine? Yes, please.)

Scientists have learned in recent years that… (A dodge to escape explaining what actually happened)

Seminal

Small molecule [To anyone other than a biochemist, all molecules are small]

Sociopolitical

Substrate [try things like dirt, mud, rock, etc.]

Sustainability (This word can mean many things, and those meanings can be profoundly important to the people using the word. But left on its own, it is an empty buzzword. Does it refer to the survive of wildlife? To the prosperity of future generations of humans?)

System (as in, “He chose mouse as a system to study”)

This (if there is no antecedent in sight)

Transmissibility

Trivial (in the way scientists like to use it: “This problem is trivial.” Non-trivial is even worse.)

Utilize (If you were telling a story to a friend and used this word instead of use, your friend might raise an eyebrow.)

Via

Virulence

We (as in “We now know the fatality ratio of the current H1N1 influenza epidemic.” We includes your readers, most of whom don’t know–yet.)

“What we need first to understand is…” Rather than tell readers what they are obligated to understand before reaching enlightenment, just enlighten us. Avoid addressing readers like students trapped in a lecture.

[Image of crier: Wikipedia]