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Jun 05 2006

Seeing the world through Darwin’s eyes

It is good to be back and blogging again!

On my trip to Australia, I had the chance to see some of the marsupial animals that are native to that continent, and as I gazed at these strange and wondrous creatures, I asked myself the same question that all visitors to the continent before me must have asked: Why are these animals so different from the ones I am familiar with? After all, Australia’s environment is not that different from that found in other parts of the world, but the fact that most marsupials (like kangaroos, wallabies, koalas, and wombats) are found only on that continent is remarkable. I was stunned to learn that when a kangaroo is born, it weighs less than one gram. This is because much of the development of the newborn (which occurs in other animals inside the womb of the mother) takes place in the pouch for marsupials.

The Encyclopedia Brittanica says that marsupials are:

a mammalian group characterized by premature birth and continued development of the newborn while attached to the nipples on the lower belly of the mother. The pouch, or marsupium, from which the group takes its name, is a flap of skin covering the nipples. Although prominent in many species, it is not a universal feature – in some species the nipples are fully exposed or are bounded by mere remnants of a pouch. The young remain firmly attached to the milk-giving teats for a period corresponding roughly to the latter part of development of the fetus in the womb of a placental mammal (eutherian).

The largest and most varied assortment of marsupials – some 200 species – is found in Australia, New Guinea, and neighbouring islands, where they make up most of the native mammals found there. In addition to the larger species such as kangaroos, wallabies, wombats, and the koala, there are numerous smaller forms, many of which are carnivorous, the Tasmanian devil being the largest of this group (family Dasyuridae). About 70 species live in the Americas, mainly in South and Central America, but one, the Virginia opossum (Didelphis virginiana), ranges through the United States into Canada.

The significance of the way that animals are distributed in the world was a key insight that Charles Darwin obtained as result of his voyage on the Beagle from 1831 to 1836. He noted that although the environment in the Galapagos Islands was very similar to that of the Cape Verde islands (off the coast of West Africa), the animal life found is each of these islands were quite dissimilar to one another and more similar to the wildlife in their immediately neighboring continents (South America and Africa respectively). This made his speculate that a few animals had arrived at the islands from the nearby continents and then changed over time to become distinctive species.

This line of reasoning caused him to doubt the dominant belief of his time (called ‘special creation’) that said that god had created each species to fit into their environmental niches. (Darwin had at one time been contemplating joining the priesthood and one can assume that he would have initially been quite comfortable with this belief.)

What would have further fuelled Darwin’s doubts about special creation was the increasing awareness, even in his own time, that large numbers of species had already gone extinct. It is now estimated that over 90% of all species that ever existed are no longer around. If god was creating each species specially to suit the available environmental niches, explaining extinction becomes problematic.

On a side note, the nature parks I visited in Australia were surprisingly relaxed about visitors. They did not keep the animals in pens separated from people, except for dangerous animals like the Tasmanian Devil. You walked around in the same area as the animals and could get up close and pet wallabies and wombats and koalas if you so wished and they were nearby. You could even enter the cages housing birds and there was no one checking to see that the doors were kept closed to prevent the birds from escaping. The rangers assumed that park visitors would not keep the doors open.

I could not imagine such a relaxed attitude in the US where people are scared that if a bird pecked someone or an animal bit or scratched a visitor, lawsuits would follow. A park ranger told me that if an animal showed signs of aggression or unwonted interest in people, they would take some action but they did not, as a rule, try to shield themselves from any chance of being sued by putting up barriers, as is the case here. He asked me where I was from and when I said the USA he nodded understandingly and said that Australia was not as litigious a country as the US, although he feared that eventually Australian nature parks would follow the US model and put up barriers between animals and visitors. (I did see tremendous American cultural dominance in their TV stations, where the programs and news formats seemed indistinguishable from their US counterparts, except for the accents.)

Seeing strange new animals in their natural habitat was very intriguing for me, provoking different feelings than seeing them in a zoo here. I can well understand how Darwin’s trip the Galapagos Islands would have triggered similar questions in his own mind and lead to his own investigations and groundbreaking theory of evolution.

POST SCRIPT: Barry’s new blog

If you have been reading the comments to this blog, you would have found some interesting and thought-provoking by Barry. Barry has now started his own blog called Those Who Can’t Teach Wish They Could where he chronicles the path of his career switch from engineering to teaching, and his observations about how the whole certification process may be discouraging otherwise talented and knowledgeable teachers from entering the classroom

Barry’s comments on my blog were always thoughtful and lively, and his blog is the same. You should visit.

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