Two recent entries in the evolution literature have application to one sex or the other.
Y, chromosome? Because it is a unique structure, the Y chromosome in human males seems more subject to deleterious mutations. The Y is also unable to distribute linked genes through recombination, a process that “makes selection more effective,” the article claimed.
Earlier claims that the Y chromosome is evolving away to extinction were premature. PhysOrg reassures males, “Men can rest easy — sex chromosomes are here to stay,” even though a study from University College London was done on chickens (no epithets, now). Humans have a unique Y chromosome in males, but chickens have a unique W chromosome in females. A research team examined how sex-linked genes on the W chromosome are passed on.
The results confirm that although these chromosomes have shrunk over millions of years, and have lost many of their original genes, those that remain are extremely important in predicting fertility and are, therefore, unlikely to become extinct.
Professor Judith Mank, from the UCL Department of Genetics, Evolution and Environment and senior author said: “Y chromosomes are here to stay, and are not the genetic wasteland that they were once thought to be.”
It was nice of her to rescue the opposite sex. Mank studied sex-linked expression of genes in a variety of chicken breeds and found that they adapt to selection pressures. She deduced that “female-specific selection related to fertility acts to shape the W chromosome, and that the chromosome is able to respond to that selection despite all the problems with the lack of recombination.” To her, this means evolvability is the key to their success:
Professor Mank said: “We have shown that Y and W chromosomes are very important in fertility – the Y in males and the W in females. It is the ability of the W-linked genes to evolve that is the key to their survival, and which suggests that both the Y and the W chromosomes are with us for the long haul.”
Oddly, this implies that survival of the fittest applies to both the XX and the XY combinations: selection has produced opposite strategies that both work.
Udder disaster: Female mammals lactate, but milk is loaded with calcium. Why don’t breasts calcify into stiff, hard structures, like bone? Just the thought is rather disconcerting to both sexes. New Scientist came along to explain “Why milk doesn’t turn breasts to bone.” (The article spared propriety by posting a picture of someone milking a cow instead of showing a picture of Madonna in concert.) First, the Darwin commercial:
Charles Darwin suggested that lactation evolved through natural selection, starting when the ancestors of mammals gained a nutritional advantage from lapping up sweat-like secretions from glands under their mothers’ skin.
This idea had some grounding. Darwin would have studied monotremes – egg-laying mammals such as the echidna. Monotremes have nipple-less mammary patches, and these secrete a fluid that provides moisture to permeable eggs.
Reporter Catherine de Lange introduced a problem: milk has 100 times the calcium and 1000 times the protein of these glands. The glands (one would think) would calcify over time, and the milk would quickly build toxic fibrils around them.
A pair of researchers, Carl Holt (University of Glasgow) and John Carver (University of Adelaide) found what keeps breast tissue soft and supple. Milk casein has the ability to “squirrel away” the stiffening calcium phosphate into micelles –naturally occurring “polar” molecular aggregates akin to soap bubbles.
The Darwin commercial came back for the last line: “Holt and Carver say that the concentration of these spherical micelles in milk may have increased over evolutionary time, producing a progressively more nutritious fluid.”
Speaking of mammals, readers may enjoy watching rare footage of Cross River gorillas, an endangered species in Nigeria and Cameroon (only 250 individuals remaining), captured on film and posted on Live Science. The clip includes a brief chest-pounding by a silverback male. See also story on Science Daily.
True to form, Charles Darwin “suggested” that something evolved over millions of years. That’s because Darwin liberated science from rigor and introduced storytelling into science. Now, instead of making scientists work the old-fashioned hard way, by trying to tie laws of nature to their effects, he introduced the power of suggestion – granting scientists the ability to employ their imaginations and weave tall tales.
His method was to introduce a new law of nature with an impressive name: “natural selection.” If it’s natural, it must be good, right? What he meant was that random variations occur. But “selection” has the feel of intelligent design about it – a problem he aggravated in The Origin by comparing it to artificial selection (intelligent design). What to do? Solution: personify Nature as an invisible Selector, scrutinizing the slightest variations, rejecting those that are bad, adding up all the ones that are good.
This introduced another problem: what is good and bad in a world ruled by contingency? Evolution is what evolution does. It’s not good or bad. Darwin pivoted by changing “natural selection” into “survival of the fittest” at the suggestion of his buddy, Herbert Spencer. But since the fitness of the fit is undefined, except for whatever increases survival, this phrase collapsed into the survival of the survivors. Whatever survives is fit by definition – even if it has traits that are opposite what another survivor has.
So, “natural selection” became indistinguishable from the Stuff Happens Law. Why are flatworms flat and roundworms round? Stuff happens. Why are sloths slow and cheetahs fast? Stuff happens. Why do normal chromosomes survive with two copies, evolving with the benefit of recombination, and sex chromosomes survive with one copy, evolving without recombination? Stuff happens.
To keep critics at bay, Darwin bequeathed to his disciples a magic wand: “millions of years.” Improbable as a given evolutionary story seems, given millions of years that no human ever observed or experienced, any stuff can happen.
This wonderful new law with its magic wand suddenly explained everything. Now, scientists can look fondly back to Father Charlie for giving them powerful new explanatory tools to tell the peasants about everything in the world. All one has to say is something “might have” evolved this way, or “may have” evolved that way over millions of years. It sounds scientific. How can anybody dispute it?
Like good Darwinians, “Holt and Carver say that the concentration of these spherical micelles in milk may have increased over evolutionary time, producing a progressively more nutritious fluid.” (Note: “Evolutionary time” is a synonym for “millions of years.”) Similarly, Judith Mank “suggests” that even though sex chromosomes have “shrunk over millions of years” they are “able to respond to selection” (meaning, they are susceptible to stuff happening).
Without this powerful army of Darwin disciples shouting “Stuff Happens” in unison and pounding their chests, ID advocates might have gotten away with announcing that the Junk DNA argument has taken another setback (e.g., Y chromosomes are “not the genetic wasteland they were once thought to be”). And nobody will be able to hear critical questions above the din: e.g., (1) Why has selection become effective with opposite outcomes? (2) Where is an unbroken chain of slight modifications between monotremes and lactating mammals? (3) Why are monotremes still around without the “progressively more nutritious fluid”? (4) Who is the engineer, and where is the squirrel, that can “squirrel away” calcium phosphate into micelles in breast tissue (but not in bone) so that lactating breasts stay soft?
Whatever other questions come to mind don’t matter, because an unheard question is indistinguishable from an unasked one.