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Evolution and Otherwise
Next week, February 12 marks the 200th anniversary of the birth in 1809 of two of the most influential men in history, Charles Darwin and Abraham Lincoln. Media of all types have either already or will shortly celebrate this anniversary. I was intrigued by the February issues of National Geographic and Smithsonian. The cover of National Geographic is emblazoned with the caption "What Darwin Didn’t Know" in big bold letters. The Smithsonian magazine has pictures of Darwin and Lincoln on the cover and one of the feature articles, by Thomas Hayden, is titled "What Darwin Didn’t Know"! The essence of the articles in both magazines is that with such developments as the multitude of fossil discoveries, the discovery of continental drift and the discovery of and subsequent studies on DNA, what Darwin didn’t know was how amazingly true his theory of evolution and natural selection would prove to be.
The last paragraph in Hayden’s article quotes biologist Francisco Ayala’s response to a question about the gaps in Darwin’s knowledge: "That’s easy, Darwin didn’t know 99 percent of what we know ... but the 1 percent that he did know was the most important part." As I’m wont to do, I went to my 1962 edition of the World Book Encyclopedia to get a perspective on how Darwin and evolution were viewed nearly a half century ago. Charles Darwin himself only rated half a page while Charles Dickens rated three pages. In fairness, the subject of evolution itself was given five pages. However, the World Book article on evolution took pains to point out missing links in the evolutionary scheme and devoted a significant amount of space calling attention to the mostly religious objections to evolution. Times haven’t changed.
In view of this anniversary, it’s virtually mandatory that I write about topics related to evolution. I’m not sure my first topic is appropriate. Last week I lunched with some former colleagues from our Bell Labs battery department. One of us is a beekeeper and we inquired about the bees and the frigid weather we’ve had this winter. He remarked that he had seen some bees emerge from the hive one day a couple weeks ago when the temperature spiked up into the 60s before plunging back to the teens and single digits. Why would the bees venture outside the hive when there obviously would be no nectar to gather?
The answer, put simply, they had to poop! I must say that I never thought about the bowel habits of bees. During the winter, the bees eat honey that they’ve stored but are fastidious in not befouling the hive. In cold weather, they would die if they ventured outside so they hold off pooping until the temperatures outside rise to a survivable level. This means holding off for weeks! How did they evolve to this stage? According to our beekeeper, honey is almost a hundred percent digestible, convertible into energy to keep the bees alive and warm without forming large amounts of waste material.
While I admit not having shed any significant light on the evolutionary history of the bee, I did find an example of evolution in another "honey eater", the subject of a very brief item on the "Wild Things" page of the same issue of Smithsonian. When one reads about Darwin, chances are that there will be mention of the finches in the Galapagos islands that Darwin visited. One thing that impressed Darwin was the different shapes of the birds’ beaks, which had evolved to different shapes depending on the flower or plant that the bird frequented to find nourishment.
In Hawaii, there used to be five species of birds, now extinct, that had curved bills. The Hawaiian birds used their long curved bills and their tongues to gather up nectar. Their curved bills closely resembled the bills of birds called honeyeaters in Asia and Australia. Until recently, it was assumed that all these birds were in the same family. However, Smithsonian researchers have now taken DNA samples from preserved specimens of the extinct birds and showed that they were not related to the Asian and Australian honeyeaters. This is one of many cases of "convergent evolution", in which unrelated families of animals evolve essentially the same physical feature for the same kind of function, in the birds’ cases, gathering nectar.
While the bit on the birds’ beaks was interesting, what really got my attention was the sea slug pictured just below Hawaiian bird item on the "Wild Things" page. Some years ago, I took my grandson to the Liberty Science Center here in New Jersey. We saw an impressive Imax movie and many interesting exhibits. As I recall, one was the actual space capsule used by one of our astronauts when he returned from space. However, the thing that intrigued me most was in an area housing various live creatures such as snakes and tarantulas. I was taken with a glass case containing what looked to me was simply a pile of dead leaves with no obvious living creature.
I was about to turn away when one of the "leaves" started crawling! This insect, whose name I’ve forgotten, had evolved a near perfect shape for camouflage in a leafy environment. Well, this sea slug in the Smithsonian has a head that looks like a normal slug or snail but its body looks all the world like a green leaf. The slug, Elysia chlorotica, is apparently a unique creature in the animal world. Why? What’s one thing that plants, with their leaves, do that no animal does? Answer - photosynthesis. Certain algae also use photosynthesis, which is essentially the combining of sunlight, carbon dioxide and water to form simple sugars and release oxygen, which allows us and other animals to exist.
The Smithsonian item was only three sentences long so I visited the Web site of Texas A&M, where researchers and workers from other universities are collaborating in studies on this leafy sea slug, which they describe as "solar-powered". In other words it can use photosynthesis to survive for months on end. This is the first known case of an animal using photosynthesis. It not only looks like a leaf, it behaves like a leaf! The sea slug eats a certain kind of alga that contain chloroplasts, the structures rich in chlorophyl that trap the sunlight needed for photosynthesis. The strange feature is that the slug digests most of the contents of the algae but the chloroplasts remain intact, building up in the slug. Eventually, the slug has built up a sufficient supply of them that it can live for nine months or so on the photosynthesis.
Hence, we have the solar-powered sea slug, the only animal known to live by photosynthesis. How can this be? It takes certain kinds of genes to accomplish photosynthesis. Sure enough, this sea slug’s DNA does contain at least one gene known to be associated with photosynthesis. It’s the only animal known to have this particular gene in its DNA. How did it acquire the gene? One possibility is that this particular gene was transferred from an alga eaten by a sea slug sometime in the past and the gene has been passed down to succeeding generations of slugs. Gene transfer is known to be especially common in bacteria and viruses, which is one reason fighting certain diseases is so difficult. If you find a drug to treat the disease, gene transfer can occur and the next year you’re confronted with a microbe with different DNA and unaffected by the drug or vaccine that worked the year before.
Sometimes evolution runs backwards. Well, not really, but Brian Trumbore called my attention recently to a curious case where it wasn’t an animal evolving but rather our understanding of three species of fish evolving to the realization that they were all just one species. An article by Associated Press science writer Randolph Schmid dated January 22 describes the work of Smithsonian ichthyologist G. David Johnson and an international team of co-workers published in the journal Biology Letters.
A type of whalefish, Cetomimidae, has been known ever since the 1800s. Strangely, the only whalefish that were caught were all females. Two other types of fish, known by their common names as tapetails and bignose fish were identified in the mid 20th century. Mysteriously, the tapetails were only found as juvenile fish while only male bignoses were found. The skeletons of the three different fish were sufficiently similar that the experts assumed the three species were related. At the same time, the fish were so different that it was not thought they could be different forms of the same fish.
However, DNA studies on fresh samples and closer study of the anatomies of the three fish have now shown that the three fish are one and the same species. The juvenile tapetails have long streamers of unknown significance. They live about 600 feet below the surface where there’s lots of food. For some reason, as the tapetails mature they go down thousands of feet to the dark depths of the ocean where food is scarce. Many deepwater fish develop large mouths and this is what the females do, even forming teeth in their gill areas that act like another mouth. On the other hand, the males clam up, literally. They apparently act like gluttons as larva and store up enough food in a huge liver to last them for the rest of their lives. Their jaws actually fuse shut and their gut shrinks, only storing some shells from meals in their youth. They stop eating!
Why do the males even bother to delve into the ocean depths and forego eating? Of course, the answer is sex. Johnson is quoted as saying that the male "... is basically a set of testes looking for the female." As might be inferred from the term "bignose", the male also develops a big nose, possibly to smell a pheromone, speculated to be released from a strange bit of tissue the female develops that is separate from the skin.
The case of these three fish merging into one species probably isn’t a good example in a column celebrating Darwin. However, it does show that some of us humans have evolved to a point where we can recognize a problem and come up with the right answer. That’s pretty impressive in itself.
Finally, for those of you following the story of Thomas Bell, the cat, I phoned our friends in Honolulu and old Tom has not been back to visit. The speculation is that, judging from his lustrous coat and well-fed condition, Thomas has found a caring family and may just return to visit our friends for old times sake or perhaps when the other family is away on a trip. This will be the last bulletin on Tom until and if he deigns to grace our friends’ home again with his presence.
Following my new every-other-week schedule, my next column will be posted on or slightly before February 19. Oh, Lincoln and Darwin are not the only birthday boys next week. Happy Birthday to our cartoonist, Harry Trumbore, celebrating only a fraction of 200 years.
Allen F. Bortrum