Darwinists Get Sexy
The origin of sex titillates many evolutionary biologists. On the one hand, animals and plants have such interesting ways of getting together. But on the other hand, sex seems too costly to have originated by natural selection. Some recent articles provide new evolutionary speculations on the origin of sex – but simultaneously undermine previous speculations.
- It all starts with multicellularity: An article in PhysOrg based on work at the Salk Institute and the Joint Genome Institute makes multicellularity a cinch: it’s “all in the family.” Work on Volvox led them to say, “One of the most pivotal steps in evolution—the transition from unicellular to multicellular organisms—may not have required as much retooling as commonly believed.” They explained, “multicellular organisms may have been able to build their more complex molecular machinery largely from the same list of parts that was already available to their unicellular ancestors.” That begs the question of where the unicellular ancestors got their complex molecular machinery, but hey: it’s just a matter of reorganizing the same Lego blocks, they said. But if “Volvox, the most sophisticated member of the lineage, is believed to have evolved from a Chlamydomonas-like ancestor within the last 200 million years,” and if “In most cases the switch from a solitary existence to a communal one happened so long ago—over 500 million years—that the genetic changes enabling it are very difficult to trace,” how can they claim that with some green algae, “the transition to multicellularity happened in a series of small, potentially adaptive changes, and the progressive increase in morphological and developmental complexity can still be seen in contemporary members of the group”? If most cases were long ago, why are there any today? And if so little retooling is required, why is there not more multicellularity evolving right before their eyes? They didn’t elaborate, but treated the origin of multicellularity as a stepping-stone to sex: “some subtypes evolved into a diffusible hormonal trigger for sexual differentiation,” the article ended, without explaining where the hormones came from.
Elisabeth Pennisi’s coverage of this story in Science1 produced another conundrum. She began by saying, “How a single cell made the leap to a complex organism is one of life’s great mysteries.” Then she quoted David Kirk of Washington University at St. Louis saying, “Even major evolutionary transitions can be accomplished via relatively subtle genetic changes.” But the very next sentence said, “As a result, solving this mystery ‘is going to take a lot more work.’” How can it be a lot of work to study a simple, albeit subtle, genetic change? She said they found “surprisingly few differences” between Volvox, a colonial organism, and Chlamydomonas, a unicellular species. Although her article did not discuss the origin of sex, the theme was that major changes can accompany simple rearrangements. Quoting Nicole King of UC Berkeley, “The key transition is not inventing a whole bunch of genes and proteins; you just have to change the way you use what you have.” - Onward to sex: An article in PhysOrg announced, “Researchers Present New Sex Evolution Theory.” This seems to presuppose that the old one is problematic or untenable. At the least, it’s inadequate: “The origin of the evolutionary game – the ability of animals (including humans) and plants to reproduce sexually, genetically recombine to repair DNA, and then produce eggs, sperm or pollen – is an unresolved mystery in biology.” So do Harris Bernstein and Carol Bernstein of the University of Arizona have the solution? Do they fulfill the teaser that they “provide insights into the early evolution of sexual organisms and the role environmental stressors had on sexual reproduction as a key survival strategy?” It sounds like their answer lies in the invention of meiosis in eukaryotes: “The UA department of cell biology and anatomy researchers argue that eukaryotes, or cells with a nucleus, adapted their meiotic ability to recombine chromosomes sexually into new genetically distinct entities from their ancestors, called prokaryotic cells.” Where did meiosis come from? They didn’t say. And a reader may wonder if eukaryotes did this on purpose according to some plan: the eukaryotes did the adapting, that sentence said, “to recombine chromosomes sexually” and create “genetically distinct entities from their ancestors”. Why would they ever do such a thing? Whatever: that ability “gives rise to eggs and sperm in humans” was the next claim – a rather giant leap down the evolutionary script. So far, we have this argument: humans reproduce sexually because meiosis arose.
The UA scientists tried to provide a motive for natural selection to create sex. “According to the Bernsteins’ theory, meiosis evolved to promote DNA repair, thereby greatly reducing DNA damage in resulting eggs and sperm.” Again, they have attributed purpose to the emergence of a complex phenomenon: meiosis evolved to do something. The passive voice verb evolved leaves the question begging of who performed the action. It doesn’t help that the next paragraphs in the article explain the benefits of DNA repair in living prokaryotes and eukaryotes. Hints of sex can be found in how prokaryotes repair their DNA, they said: “Transformation is the transfer of a fragment of DNA from a donor cell to a recipient cell, followed by recombination in the recipient chromosome. The researchers call this bacterial process an early version of sex.” Why prokaryotes stopped there billions of years ago, and are still around today with their primitive proto-sex, was not explained.
The Bernsteins dispensed with the old to make way for the new: “The prevailing theory is that eukaryotes developed the ability for meiosis and sexual reproduction from their ability to reproduce through mitosis and not from their early ancestor’s ability to reproduce through transformation.” In with the new: “Our proposal, that the sexual process of meiosis in eukaryotes arose from the sexual process of transformation in their bacterial ancestors, is a new and fundamentally different perspective that will likely generate controversy,” they predicted. Their proposal has advantages: “If it is assumed that meiosis arose only after mitosis was established, there would have been an extended period (while mitosis was evolving) when there was no meiosis, and therefore no sex, in eukaryotes,” they explained. “This assumption appears to be contradicted by evidence that the basic machinery for meiosis was present very early in eukaryote evolution.” So assuming meiosis “arose” earlier, and was already there, the origin of sex follows. This is a displacement explanation. Meiosis did not have to evolve in eukaryotes: it was already there. Adding a little stress pushed the evolution of sex: “A key argument in their hypothesis is that in both prokaryotes and simple eukaryotes, sexual cycles are induced by stressful conditions,” they continued. “Thus, the recombinational repair promoted by transformation and meiosis is part of a survival strategy in response to stress.” Stress is the mother of invention – in this case, sex.
In passing, they shared some interesting information about DNA repair: “the average human cell incurs about 10,000 DNA damages per day, of which 50 are double-strand breaks.” It’s a wonder cancer is not more prevalent. The reactive oxygen molecules produced from food you eat are responsible for many of these breaks. “Thus, efficient DNA recombinational repair is an adaptation for cell survival and for producing new offspring, in higher organisms, through meiosis,” the article concluded. Sex is not about love; it’s about avoiding DNA damage. How the vast majority of organisms (microbes) got by without it from the beginning of life till now is not quite clear. - Ancient seed: The news media are reporting that “Sperm in All Animals Originated 600 Million Years Ago.” Live Science said that; Science Daily put it, “Human Sperm Gene Is 600 Million Years Old, Scientists Discover.” This gene, named Boule, is found in fruit flies and humans, so according to evolutionary theory, it must be so important, that despite the ebb and flow of evolution over the whole span of multicellular life, this one escaped virtually unchanged.
“Just as styles in sexy clothes or fashion change from year to year and culture to culture, ‘sexy’ genes, or genes specific to sex, also change rapidly,” Science Daily said. “But there is one sex-specific gene so vital, its function has remained unaltered throughout evolution and is found in almost all animals, according to new research from Northwestern University Feinberg School of Medicine.” In Live Science, Eugene Xu of Northwestern was stunned: “It’s really surprising because sperm production gets pounded by natural selection,” but this one did not. “It tends to change due to strong selective pressures for sperm-specific genes to evolve. There is extra pressure to be a super male to improve reproductive success,” he said. But even superman cannot evolve against this gene. “This is the one sex-specific element that didn’t change across species. This must be so important that it can’t change.” Evolution is inexorable – except when it’s not. - Sex and necks: Giraffes have sex. They also have long necks. The old, traditional evolutionary explanation for the long necks is that giraffes needed to reach higher up the trees. That’s so Lamarck. Bosh; necks are for sex, argues Rob Simmons and Res Altwegg of the University of Cape Town in South Africa. Michael Marshall on New Scientist gave press to this idea: “The latest theory – and it’s a surprise this hasn’t come up before, given biologists’ fixation with it,” (i.e., sex) “– is that the long necks are the result of sexual selection: that is, they evolved in males as a way of competing for females.” First, though, he had to dispense with the traditional view: “The evidence supporting the high-feeding theory is surprisingly weak,” he said. “Giraffes in South Africa do spend a lot of time browsing for food high up in trees, but elsewhere in Africa they don’t seem to bother, even when food is scarce.”
Male giraffes, though, do go through a ritual of “necking” as a form of conquest. They stand side by side and ram each other’s ribs and legs with their ossicones (the pointed growths on top of their heads). “Having a long and powerful neck would be an advantage in these duels, and it’s been found that males with long necks tend to win, and also that females prefer them,” explained Marshall. It also explains why the necks evolved faster than the legs, he said. Having a long neck, though, is the question. A need is not a mechanism for getting something. The presumption is that some early short-necked male pre-giraffe lost to a rival having a neck slightly longer. He fathered all the babies, and natural selection continued to magnify that trait. But did the necking habit evolve before or after the necks got long? Why didn’t the rival develop ram’s horns to batter the long-necked rival in the side? Any evolutionary explanation also has to account for the many internal changes that come with a long neck – a powerful heart, special blood vessels, and protection for the brain when the animal leans over to get a drink. Presumably natural selection took care of all these problems simultaneously.
Every solution creates new problems. Why, if males “evolved” long necks to do battle, do the females have long necks? Not every exaggerated traits in males are echoed in females (think peacocks). Graham Mitchell of the University of Pretoria in South Africa produced evidence that male and female giraffes in South Africa have necks of identical length. Simmons and Altwegg, however, countered that the males’ necks are slightly longer, and heavier. In the end, they opted for a composite evolutionary explanation: “Simmons and Altwegg suggest that giraffes’ necks may have begun growing as a way of eating hard-to-reach food, but that they were then ’hijacked’ for mating purposes,” Marshall explained. “Once the necks had reached a certain length, males could use them for necking and clubbing – and at that point sexual selection took over, driving the necks to their current extreme lengths.”
1. Elisabeth Pennisi, “Volvox Genome Shows It Doesn’t Take Much to Be Multicellular,” Science, 9 July 2010: Vol. 329. no. 5988, pp. 128-129, DOI: 10.1126/science.329.5988.128-a.
Didn’t he just say that ”the evidence for the high-feeding theory is surprisingly weak”? And even if the long necks started stretching for feeding, why didn’t the female necks stop once the males hijacked the necks for mating purposes? Maybe the females needed to keep stretching their necks to see eye-to-eye with the big boys. Who knows; once composite explanations are offered, any combination of stories might do.
To understand science articles these days, you need to learn how to brush past the bluff. All the happy-happy talk about how such and such a “finding” sheds light on evolution is like advertising at a used car lot. If it’s a road-worthy car you are after, you must tune out the ribbons and flags and balloons, the billboards of scantily-clad women standing by the cars, the P.T. Barnum salespeople with their Bengal tigers and jugglers, and go for the data. Kick the tires, open the hood, check the fluid levels, and know ahead of time what the value of the vehicle should be. Take it for a test drive: what happens when you have to drive it up hill? Sure, the DarwinMobile rolls downhill with ease, but put it into low gear and see if it can handle the steep grades. You wouldn’t trust any one of these explanatory vehicles above with your wife and kids. Unfortunately, the science community, the popular press, and the researchers have a monopoly on DarwinMobiles and that’s all they have to sell. You need to go to independent dealers to get an explanatory vehicle that is intelligently designed for the real road.
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