Some time ago I came across a very nicely done Flash animation showing how the universe and Earth have developed to this point:
evolution — what next?.
The site features a timeline with a slider you can drag. It starts at the big bang, an estimated 13.7 billion years ago. Once the solar system forms some five billion years ago, it focuses on Earth. Since the most interesting things, from a human perspective, have happened recently, there are a series of supplemental sliders to focus on the most recent portion of each timeline. With simple animations, it’s a nice, easy way to visualize the history of our planet, and see just where our little story fits in.
An illustration of Tiktaalik roseae from Wikipedia. Credit: ArthurWeasley.
In the last several years, scientists have mapped in detail the lines of descent that resulted in aquatic vertebrates (fish) being able to survive and function outside water—including lines of descent that today have resulted in the mammals. Periodic discoveries stimulate interest in the media, such as the discovery last year of the 375-million-year-old Tiktaalik, or occasional sightings of coelacanths, an order of fish once thought to be long-extinct. But how are these animals related to each other and to us?
New Scientist published an article last week discussing new research into the coelacanth’s fins (specifically, when the difference between the coelacanth’s symmetric appendages and our asymetric appendages arose). But what I found especially interesting was a graphic demonstrating the relationships between extant lifeforms and notable extinct relatives, including when they are thought to have lived.
See full-sized image. Source: New Scientist.
Perhaps this will help provide a framework when reading about these fascinating animals.
As I mentioned in my previous post “Evolution Sunday,” today is Darwin Day, the anniversary of the birth of Charles Darwin.
Darwin’s principles provide the fundamentals of modern biology and medicine and have contributed to other fields of science as well. His work helps us understand where we came from and where we are going, to understand the history of this planet.
Happy Birthday, Charles Darwin. Thank you for everything you taught us.
As our scientific understanding expands, it has naturally provided different explanations than the accounts given in the mythologies of the various religons. For the most part, religions long ago abandoned attempts to explain the natural world, leaving such mundane details to science and instead focusing on matters such as philosophy, morals, and ethics, as well as purely religious concepts such as spiritual salvation. The one notable attempt to continue following religious accounts, rather than scientific ones, is that regarding biological evolution. Primarily among some members of the Christian faith in the United States, proponents have gone so far as to attempt to remove selected scientific theories from public schools or even to teach their religious accounts alongside them, as if they were alternative theories instead of rooted in religious stories.
Naturally, such an action is unacceptable to those in the scientific community, and indeed, to many in the religious community (the two are not mutually exclusive, of course). Some people perceive there to be a conflict between science and religion. But science is agnostic on the subject of God. It neither affirms nor denies God’s existence, but rather seeks to find simple explanations for observations without invoking supernatural forces. And of course, many people believe that religion and science serve different functions, that explaining what lightning is or how the Earth was formed is better analyzed through science.
Continue reading “Evolution Sunday”
Doonesbury, published on 14 January 2007. See full-sized version.
Teaching the controversy is fine, as long as one is clear that the controversy is a social/religious one and and not a scientific one.
To date, astronomers have discovered about 209 extrasolar planets; that is, planets outside our solar system. From Earth, it is quite difficult to even detect them, much less learn anything about them. We haven’t been able to determine much about these planets—usually only the mass—though we’ve been able to get glimpses of atmosphere in a couple cases.
Of course, we have no idea if there is life on other planets, or how we might detect it. One way to think about it is to imagine what other life forms might think of Earth if they were to stumble across it.
Continue reading “What Does the Atmosphere Say About Earth?”
I just wanted to let you all know that Oludvai George has posted another entry showcasing his beautiful illustrations, this time looking at some cat-like animals in the order Carnivora. Take a look and enjoy these fascinating peeks into the life that preceded us.
Source: David M. Hillis, Derrick Zwickl, and Robin Gutell, University of Texas
In my previous post I mentioned “Pale Blue Dot,” a photograph taken by Voyager 1 from the outer reaches of the solar system showing Earth as a barely visible dot of light. But even on Earth, we humans are just one in a family of millions.
Brett Keller discusses in his blog Brett Keller & the World a remarkable “tree of life” published a few years ago in the prestigious journal Science. This “tree,” arranged in a circular format, was developed by David Hillis and colleagues at the University of Texas. They selected around three thousand species, trying to include representatives from all major groups. You may read more about it and see where our species, Homo sapiens, fits in at Mr. Keller’s blog.
Possible phylogenetic tree
These representations, more formally called phylogenetic trees, are intended to illustrate the evolutionary relationships between species. Lines are drawn from two species (call them A and B) that are closely related, meeting at a vertex called a “node” representing the most recent species that is ancestral to the both of them. Another node may occur further up, representing the most recent common ancestor of the A-B ancestor and species C, and lines will be drawn to both of those. And perhaps even further up is the ancestor to species A, B, C, and D, with one line going to the A-B-C ancestor and one going to species D.
Continue reading “Family Circle”
Dolphins are my favorite animals, and I’ve always been fascinated by their interesting evolutionary path. Dolphins and whales (that is, cetaceans) are mammals like we are: they breathe air, they give birth to live young, and their spines bend up and down like ours do (not side to side like those of sharks or other fish). And like us, they are descended from four-legged land mammals. It’s quite interesting to examine the sequence of changes that resulted in them more and more adapted to living in water.
Examination of a dolphin skeleton clearly reveals our closely shared ancestry. In addition to the similar spines (vertebral columns), in their flippers, dolphins have the same bones we do in our arms. Connected to the scapula (shoulder bone) is a short humerus (arm bone), then a short radius and ulna (forearm bones), followed by the tarsals (wrist bones), metatarsals (hand bones), and phalanges (finger bones)—dolphins (and whales) have five “fingers” inside their flippers. And often tiny, vestigial hind leg bones are found buried within the animal. In fact, there was a CNN article a couple weeks ago (“Could extra dolphin fins be legs?”) discussing a dolphin with a pair of caudal fins perhaps representing the ancient hind limbs:
TOKYO, Japan (AP) — Japanese researchers said Sunday that a bottlenose dolphin captured last month has an extra set of fins that could be the remains of hind legs, a discovery that may provide further evidence that ocean-dwelling mammals once lived on land.
Fossil remains show dolphins and whales were four-footed land animals about 50 million years ago and share the same common ancestor as hippos and deer. Scientists believe they later transitioned to an aquatic lifestyle and their hind limbs disappeared.
Whale and dolphin fetuses also show signs of hind protrusions but these generally disappear before birth.
If you’re interested in more about this fascinating progression, artist Carl Buell has started a series of posts on cetacean evolution at his blog Olduvai George (which I noticed courtesy of Pharyngula). He’s just posted the first in the series, with a nice commentary accompanied by his excellent illustrations. Take a look!