This may seem obvious. But in evolutionary terms, the benefits of sexual reproduction are not immediately clear. Male rhinoceros beetles grow huge, unwieldy horns half the length of their body that they use to fight for females. Ribbon-tailed birds of paradise produce outlandish plumage to attract a mate. Darwin was bothered by such traits, since his theory of evolution couldn't completely explain them ("The sight of a feather in a peacock's tail, whenever I gaze at it, makes me feel sick!" he wrote to a friend).
Moreover, sex allows an unrelated, possibly inferior partner to insert half a genome into the next generation. So why is sex nearly universal across animals, plants and fungi? Shouldn't natural selection favor animals that forgo draining displays and genetic roulette and simply clone themselves?
Yes and no. Many animals do clone themselves; certain sea anemones can bud identical twins from the sides of their bodies. Aphids, bees and ants can reproduce asexually. Virgin births sometimes occur among hammerhead sharks, turkeys, boa constrictors and komodo dragons. But nearly all animals engage in sex at some point in their lives. Biologists say that the benefits of sex come from the genetic rearrangements that occur during meiosis, the special cell division that produces eggs and sperm. During meiosis, combinations of the parents' genes are broken up and reconfigured into novel arrangements in the resulting sperm and egg cells, creating new gene combinations that might be advantageous.
One animal, however, has done just fine without any sex at all. Bdelloid rotifers can be found in most freshwater ponds, measure a few tenths of a millimeter long, contain only about 1,000 cells, and have been chaste for roughly 80 million years. The nearly 400 described species of bdelloids prove that the group is respectably diverse, yet no one has ever seen a male. Bdelloids lay unfertilized eggs that grow to be fully fertile daughters. What's the secret?
Harvard University biology professor Matthew Meselson and his lab have spent the past several years investigating bdelloids' molecular genetics. By exposing bdelloids to extremely high levels of ionizing radiation (a treatment that causes hundreds of physical breaks in DNA strands), one of Meselson's former graduate students, Eugene Gladyshev, showed that bdelloids can completely rebuild their genomes—an unprecedented feat among animals.
Recently, Meselson and Gladyshev made an even more amazing discovery: Bdelloids have foreign DNA from bacteria and fungi in their chromosomes, which is a great way to maintain genetic diversity. As for the rest of us, we're stuck with sex.
This article originally appeared in the May 2011 issue of Popular Science magazine.
plants can clone, however i would imagine that cloning several times would be similar to photo copying a picture to many times it will be eventually blurry or something like that...
All I have to say about this whole article is why?
There is no point in talking about the point of sex. Is this your first article?
It is foolish waisting time writing articles like these when there are plenty of better things to talk about. You should be talking about cures and experiments that have some in depth impact on our society. Sex is a common thing between man and a woman. We already know about that.
That's a dull way to make money. Writing articles like these.
Please write about more important matters. You are a Popular Science writer after all.
@aerosphere It seems you don't have an enquiring mind. If all scientists were to settle for the answer "We all know that" they would never have discovered the things they did.
Re: the article - one thing worth mentioning is a theory written about in the book Parasite Rex, which (based on studying snails) states that sex is a means to stay ahead of parasitic organisms. The more random effect of sex vs. cloning makes it harder for a parasite to find ways around a species' immune system.
The snails in question, found in New Zealand I believe, changed from asexual to heterosexual during periods when parasite attacks became more prolific.
"Darwin was bothered by such traits, since his theory of evolution couldn’t completely explain them (“The sight of a feather in a peacock’s tail, whenever I gaze at it, makes me feel sick!” he wrote to a friend)"
Thats kind of funny since it's common knowledge.
It's not an evolutionary trait, but a selective breeding trait.
The tail is what female like, so they breed more with birds that have that tail.
Thus, women are controlling the evolution of the species based on their preferences.
Yes, but the point is, why do species which waste their energy supporting more and more flamboyent displays to compete for mates exist in the first place. How is the waste of energy not hurting their survival chances enough to extinguish the species? The growth wasted is enourmous, as is the time. Not to mention, if I was a preditor, I'd love an animal that grew a ty-dye set of feathers.
There are some justifications for it; one is that during mating, higher amounts of testosterone reduce the immune system; therefore peacocks that can maintain such a display basically say: "Look at me. Even with diminished immunity, I can maintain this beautiful exterior. My genes are awesome". Mating displays during periods which coencide with elevated testosterone do have the effect of removing the veil the immune system places over the genes, but that just improves the method of selection from the same group of flamboyent animals. It still doesn't seem like a sufficient explanation for why species with less-demanding females don't overcome these inefficient animals.
Fortunately, just because there's a metaphor that makes it seem logical, that is not the case. You yourself are an organism that is made from cells that have copied their genetic code Trillions upon Trillions of times; just in your lifetime. The important thing about reproduction is that it copies perfectly (yes, some random variation do to environmental damage of gametes, but that isn't the issue here). While the method of cloning has to itself be robust (make sure telomeres are long, among other things) then organisms can clone themselves over and over and over again. Asexual reproduction that some plants participate in is precisely biological cloning.
Well, I can't agree with aerosphere but the article seems overly simplistic to me. I think complex animals (not 1000-cell whatchamacallits) need to select mates based on what they perceive to be desirable traits. They can not afford to play hit and miss like simpler organisms which have no other choice.
Also, just like empires and civilizations, there is a rise, peak and fall for any given species. During the peak time, there is the ability to 'waste' resources. At their height, a particular species may not be under serious threat. I would think that is when these so called 'draining displays' would have evolved. These developments have specific purposes so are not really wasted and can be easily afforded during less stressful periods in the lifespan of a species. Of course, they can be draining when the species is in decline but evolution doesn't have foresight!
Finally the idea that those simple organisms replicate just by cloning seems to be missing something. If that were true, there would be no 'class' containing 400 species. After billions of generations of countless individuals cloning, along with bringing in foreign DNA, there would be uncountable variations and species of these critters. Something must be keeping the class relatively intact.
There's also the nematode worm if you're looking to find bizarre ways of having sex (at least if you're prone to anthropomorphising) as they're all either male or hermaphrodite, with the hermaphrodites literally able to have sex with themselves.
One omission in the article though worth highlighting is in your brief discussion of the benefits of sex which is really what makes studies like this interesting. One key concept to keep in mind is that chromosomes are physical entities and how these are given to the offspring is in a large way what sex is about.
Chromosomes can be thought of as beads of genes on a string of DNA, and in an organism capable of having sex the sister chromosomes (one from each parent) are separated off and packaged into the sperm or egg cells. The key point being that by having redundancy (in the form of two slightly different copies of each bead on the sister chromosomes) the effects of both good and bad mutations can be moderated, and this encourages diversity by reducing the selective pressures on the current generation.
In this way, it follows that organisms that have sex have the freedom to 'make evolutionary mistakes' in terms of mutations and the like, without being punished for it straight away - but also that a great gene arising on a chromosome with loads of rubbish genes won't be found guilty by association. That is to say, the great gene won't be immediately erased from record with the death of the organism - as it would be with an asexual organism with only a single copy of a chromosome and no good genes on another chromosome able to compensate the bad ones. Obviously no-one really knows exactly what 'nature's thinking' is when it comes to things like this, but this is one impact of reproducing sexually that helps to put this research into context.
I once read in a sci fi book that sex is what life is all about.
Sounds like the Asari from Mass Effect.
They only reproduce daughters but take genetic material from foreign sources such as alien humanoids.
LOL...life imitating art?
The point in sex is that it fills good of course. I also like sex with myself.
Women fuck because they like big penises and money. Men fuck so their children can become women...
LOL! So one can brag about it to their friends of course. Example: Bro, I pulled a hat-trick last night! It was epic!!
Old article and old comments.
Popsci has started to supplement with recycled articles. Sadly, they do not even bother to repost them, but leave the old replies in place. I haven't tested the links - but I'm sure they are often duds.
They have also taken to not putting comment boxes under certain articles, like the propaganda piece about the army leak who thinks he is a woman.
It's known that about 50% of the human genome is of viral and bacterial, but supressed, origin. Don't open Pandorra's box.
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