Why do humans have a fascination for the "extra large"? Our flat screen TV's are constantly growing in size... some can't resist the urge to "supersize" that fast food meal... and, when it comes to life in the past, we tend to have a fascination with the extra-large as well. This explains the success of such movies as Jurassic Park. We are fascinated with this world of the past where life was, well... "larger than life". In reality, our perception that "everything was bigger long ago", isn't really very accurate. Early life on Earth was mostly microscopic, and the largest known animals that have ever lived on Earth are still with us today. Yes, some of today's whales are far larger than even the largest dinosaurs of the past. |
It may be natural to romanticize the past and focus our attention on the biggest and the baddest of those times, but recent research indicates that even the "biggest and the baddest" might not have been so big... and were perhaps a little too "bad". Case in point... the Wooly Mammoth. For nearly 700,000 years these ice age pachyderms were among the most common large herbivores of the Northern hemisphere. But then, about 10,000 years ago the population began declining rapidly. Since this decline coincided closely with then retreat of the glaciers at the end of this most recent ice age, it was natural to assume that it was simply the changing climate (global warming?) of the time that the mammoths simply couldn't adapt to. Then, new evidence began pointing to a new culprit in the demise of the mammoth... early man. It seems that where early man settled, mammoths soon disappeared from the landscape. Mammoth bones found from this time show clear evidence of violent encounters with our distant ancestors. Spearpoints embedded in bone; scrape marks on bones showing where stone tools were used to cut away meat; etc...
For many years, we believed that the last of the mammoths disappeared nearly 10,000 years ago... but not so fast! Newer discoveries indicate that small populations of mammoths continued to exist on several smaller, isolated islands (maybe our hungry ancestors didn't find them there) for another 6,000 - 7,000 years! These island populations of mammoths evolved over time into much smaller versions of their giant ancestors, standing only 1/3 as tall as the extinct mainland version. Why did these pygmy mammoths become extinct? Perhaps humans finally discovered them and finished the job they started thousands of years before? A recent study indicates that it may have been the isolation that led to the eventual downfall of these last remaining mammoths. Using new genetic analysis techniques, it was found that there was an unusually high number of harmful gene mutations in these isolated island populations as compared to older specimens from the mainland. These harmful genetic mutations may have led to the final demise of this species. |
In normal situations, natural selection works to eliminate harmful mutations from the gene pool, but in isolated populations, inbreeding among closely related individuals tends to multiply the number of these mutations. With no access to outside, unrelated bloodlines, the island populations were eventually betrayed by their own DNA as they slowly slid into extinction.
Is there a lesson for us today? Perhaps. We often wait until an endangered population is on the brink of extinction before we mount efforts to save the species. Captive breeding programs may be set up to increase the perilously low numbers. If the effort is successful in increasing the population, how much genetic diversity still remains? Will this species eventually show the same level of harmful genetic mutations due to inbreeding as was seen in the final small pockets of pygmy mammoths? Conservation efforts must be put into place before the gene pool becomes too "shallow" to sustain a healthy population. This is a lesson that we can learn from the "story of the mammoth".
More about the new genetic research on mammoths can be found here... http://www.livescience.com/58088-woolly-mammoths-doomed-by-dna-mutations.html
Is there a lesson for us today? Perhaps. We often wait until an endangered population is on the brink of extinction before we mount efforts to save the species. Captive breeding programs may be set up to increase the perilously low numbers. If the effort is successful in increasing the population, how much genetic diversity still remains? Will this species eventually show the same level of harmful genetic mutations due to inbreeding as was seen in the final small pockets of pygmy mammoths? Conservation efforts must be put into place before the gene pool becomes too "shallow" to sustain a healthy population. This is a lesson that we can learn from the "story of the mammoth".
More about the new genetic research on mammoths can be found here... http://www.livescience.com/58088-woolly-mammoths-doomed-by-dna-mutations.html