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To Mate, Or Not
CHAPTER 77 Getting Together, Maybe Not
Regular readers of this column will know that I am a big fan of the work of Svante Paabo and his group at one of the Max Planck Institutes in Germany, where they managed the very difficult task of decoding DNA from ancient fossils. I was particularly excited about their work showing that we who trace our ancestry back to Europe have in our DNA a few percent of our genes traceable back to Neanderthals having sex with modern homo sapiens. I don't know, did it make me feel more masculine to think I'm partly related to those brutish savages we thought the Neanderthals were? Or were they? In the January 17, 2017 magazine section of the Sunday New York Times there is a very interesting long article by Joe Mooallem titled "Us and Them", which deals with the developing view that the Neanderthals were not those ignorant brutes so long assumed, but were people much like us in our ancient selves.
Joachim Neander was a poet theologian who wandered about in a valley near Dusseldorf, Germany back in the 1600s. He wrote hymns about the valley and its beauty and the valley became the Neander Valley. In 1856 workers in a quarry there dug up a skull, mistakenly assumed to be a Cossack's skull and the prominent bony ridge over its eye sockets was postulated to result from the Cossack's furrowing of his brow because of pain due to rickets! Some 8 years later, British geologist William King published a paper suggesting that the skull actually belonged to an extinct human species he called Homo neanderthalensis, Neanderthal Man. Focusing on what he called the "enormously projecting brow" and, given the times, King concluded the skull showed the Neanderthal to be stupid and a brute. What King didn't know was that another British scientist, George Buck, had received a skull that had been dug up in Gibraltar long before the Neander skull. This skull was a woman's skull and didn't have as impressive a bony ridge as the male skull. The Times article speculates that if Buck had been first to report on a Neanderthal skull, the "brutishness" of the species might not have been assumed.
Mooallem describes his own experiences when he joined those who are still digging in caves in Gibraltar and cites findings of numerous bits of evidence that the Neanderthals were really not stupid brutes but were much like us as our very early selves. They built fires, made axes, cooked meat and, for example, knew how to take advantage of a natural chimney inside a cave to build a fire to keep them warm. In one cave there was an extensive hash tag kind of scribing on a rock slab. Why did the Neanderthals go extinct? Mooallem leans towards the Neanderthals simply having such a low population density that, instead of being wiped out by the invading homo sapiens in battle, there just weren't enough Neanderthals not to be overwhelmed by us moderns and they simply faded away.
There was another species that went extinct that was much more dominant than the Neanderthals, the dinosaur. An asteroid or comet played a key role in that extinction. The estimated six mile radius asteroid or comet that struck our planet may have been accompanied by major volcanism as the ultimate cause or causes of the dinosaur's extinction. Naturally, one has good reason to worry about the possibility of another object from space hitting Earth somewhere and causing our own human demise. In the February issue of National Geographic there's an interesting dialogue between two unlikely characters, Neil DeGrasse Tyson and Whoopi Goldberg, that touches on the possibility of an asteroid or comet hitting Earth and what we should do to prevent it from doing so. Whoopi has an interest in such things and talks of her desire to be in a Star Wars movie. Tyson points out that should we find an object that is going to strike us in the future, we really need to detect it well before it makes its final approach to hitting us. If we detect an object that will hit us in a future orbit he suggests shining a laser on its bottom surface to make it outgas, thus changing its orbit enough not to be a problem. He feels if the object is already on a direct path to hit us it's too late to take effective action.
In my opinion, instead of building a wall, our new president should spend the money building a more robust system to detect such possible threats to our existence on Earth. I've been talking about asteroids or comets but did you know that there's actually a star headed for our solar system? The European Space Agency's Gaia satellite has done an incredible job of determining the positions and motions of over a billion stars in our Milky Way galaxy. Such an achievement boggles my mind. And they have found a small star, Gliese 710, that is actually headed for our solar system. I don't know about you, but to me the idea of a star passing anywhere near our solar system is a big deal.
Predictions are the star will pass through the outer reaches of our system, the Oort Cloud, with all sorts of objects way out there beyond Pluto. One possible effect of a star passing through this region is that it could deflect the paths of various bodies in the Oort Cloud and send comets on paths that could intersect the paths of planets such as our Earth. Oh well, I'm going to stop worrying about this possibility. It won't happen for another 1.3 million years from now and, who knows, we may all be extinct by then.
Back to Earth, following the article featuring Tyson and Whoopi in National Geographic, there' a picture of what I consider to be one of nature's cutest animals, the meerkat. The little guy or gal is sitting upright staring at me with its big round eyes. The subject of the one-page article accompanying the picture is about sex and weight gain, not what I expected to accompany the picture. The article, "Throwing her weight around" by Patricia Edmonds, says that a typical meerkat colony may have as many as 50 members but in that sizeable group only two individuals have sex with each other!
There's a dominant male and a dominant female who have a monopoly on mating and producing pups. The rest of the colony carries out other duties such as sentry duty, burrowing and babysitting. Understandably, male meerkats who are not the dominant male often leave the colony. Females who are not dominant and make the mistake of becoming pregnant are either heckled until they abort, or if they have pups, the pups may be killed. Not a good idea to deviate from the norm. The meerkat society is one society in which it pays to be on the heavier side. When a dominant female dies it is usually the oldest and heaviest female that takes her place.
Now that we've established the sexual customs in the meerkat society, let's turn to another species. I was perusing the PopChart page of the February 6 edition of Time magazine and found a sentence stating that a female zebra shark in an Australian aquarium had given birth to three sharks even though it had been separated from its mate for three years! In other words the presumption was that this was a case of asexual reproduction, an immaculate conception so to speak. My first thought was that I hope those associated with the aquarium would look at the DNA of the offspring. That should confirm that indeed there wasn't some male shark that had sneaked into the female's tank.
Well, I was going to leave it at that but decided to Google the subject and, sure enough, found that there was much more than that one sentence in the magazine. The University of Queensland Web site cites the work of faculty member Dr. Christine Dudgeon, who documented the case of the leopard (not zebra) shark Leonie, the first shark recorded to have had offspring with a male shark and then switch to having babies without the benefit of a father. I must admit that I had forgotten that a shark is not a mammal and lays eggs. Apparently it is not unusual for a shark, like a chicken, to lay eggs without being fertilized. Leonie had been swimming around with a male companion for some time when space needs resulted in the male being removed from the tank. Leonie went through three mating seasons without a partner. Last year, aquarium personnel noticed that Leonie had laid some eggs and that three of them had embryos in them. Three sharks were hatched.
The Queensland researchers wondered if this may have been a case of stored sperm and they did indeed look at the DNA. All the cells were from Leonie, confirming asexual birth. This finding generated more than the usual excitement in that the leopard shark is an endangered species and the female's ability to self generate fertile eggs could be a means to produce more offspring. The Queensland workers are also quite interested in seeing whether the asexually birthed offspring can mate successfully with male sharks or produce offspring on their own. Of course, whatever the case it won't generate the headlines spawned by the announcement that Beyonce is having twins.
Next column on or about March 1, hopefully.