Category: Blog
I’ve revisited the wrist walker story after a scientist involved accused me of spreading “empty gossip.” I don’t agree with that charge, but I do think I should retract some of what I wrote. But I’ve still got some nagging questions about the whole affair. Check it out.
Originally published March 9, 2006. Copyright 2006 Carl Zimmer.
I’ve been in low-blogging mode for a few days as I try to fire off a few dead-tree articles. But I wanted to write up a quick post to draw your attention to threetwo very interesting pieces of human evolution in the news.
1. Modern evolution. A new paper presents the results of a systematic scan for human genes that have experienced natural selection in the past few thousand years. An impressive 700 regions turned up. The fact that humans have been evolving during recorded history is not new. The ability to digest lactose in milk as an adult, resistance to malaria, and other traits have long been recognized as having experienced strong natural selection after the dawn of agriculture.
Scientists are probably centuries away from drawing the full tree of life. For one thing, they have only discovered a small fraction of the species on Earth–perhaps only ten percent. They are also grappling with the relationships between the species they have discovered. Systematists (scientists who study the tree of life) rely mainly on DNA these days to figure out how species are related to one another. They compare the similarities and differences in a given gene in several different species to figure out which ones share the closest kinship. But they have actually sequenced DNA from relatively few species. And in many cases, that DNA may come from a single gene.
This image came out a couple months ago in Nature, but I just came across it today. I quite like the way it sums up the history of life–something that’s maddening hard to do, since the time scales are so vast. It shows how life’s diversity has been accumulating for billions of years. This chart shows the timing of the earliest paeolontological evidence for different kinds of life, ranging from fossils to chemical markers. A few definitions may help.
Go back far enough in our history–maybe about 650 million years–and you come to a time when our ancestors were still invertebrates. That is, they had no skulls, teeth, or other bones. They didn’t even have a brain.
How invertebrates became vertebrates is a fascinating question, made all the more fascinating because the answer tells us something about how we got to be the way we are. In order to reconstruct what happened, scientists can study several different kinds of evidence.