Re: How did dinosaurs become extinct? What are main theories?

Guillermo,

The internet makes it possible for people to share information faster and to a wider audience than has ever before been possible. But the other side of this new technology is that bad ideas can also get spread without anyone checking the facts. While the site you were at on world population growth is not a sham, the site it linked you to titled "Neither catastrophes nor gradualism caused the extinction of the dinosaurs," is a sham.

The first clues are the subtitles: "Science Series 'An Alternative to Mainstream" and "Articles for the informed layman." Of course almost all currently accepted scientific thought was at one time not "mainstream," but the authors of these ideas took the trouble to get their ideas published in peer reviewed journals, after which they were gradually accepted as evidence mounted in their favor. In contrast, the author of this website presents no new data at all, and isn't even aiming his ideas at scientists in the relevant fields. When you run into someone trying to escape doing real science and instead taking his/ her story straight to the public, this is usually a good sign that the author is not doing science.

In direct contrast to what the website says, the vast majority of species have gone extinct do to gradualistic change, either do to the species' evolution into another species (called allopatric speciation), or else due to local competion and/or environmental change. There are a few events in Earth's history that appear to have been caused by events of catastrophic proportons: the Cretaceous extinction is one of these, as is the Permian-Triassic extinction. Both of these have been tied to meteor impacts.

The website's author refers to a "Curve of Life," which is not a concept that is recognized in the scientific literature. It's true that caged rat populations have followed a curve like this, but there is no known correlation with studies of modern ecology. When food sources increase, local animal populations often increase beyond sustainable levels, only to crash when the food sources decrease due to environmental change or over-use of the food resources. This boom and bust cycle usually is localized, and never has anyone seen a species go extinct under these circumstances.

In fact, studies done on the Galapagos finches by Peter Grant suggest that this cycle of population boom and bust is a valuble part of the evolutionary process. The boom cycle increases a species' genetic diversity, increasing its flexibility to adapt to rapidly changing conditions. The ensuing population crash then acts as a selective pressure, driving changes in both morphology and in mate selection preference. In short, the author of that webpage is simply wrong; he is citing supposed "insights" that are actually a normal part of a healthy population.

Humans may well go extinct in the future, but the possibility is hardly likely to occur in the very near future. And if it does, it will be the fault of careless and uniformed choices, rather than due to a predetermined "Curve of Life."

Scott Hartman
Tate Museum