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The Catharus thrushes are a group of somber-colored songbirds that breed widely across North America, generally in deep, dark, moist forests. Their songs are considered among the most beautiful, with reedy, flutey phrases and internal harmonies produced within the muscular syrinx. These birds are at once familiar and foreign - they remind us well of their close taxonomic ally, the Robin, but they are not nearly so often encountered by average folks on the street, as they spend summers in their deep forest recesses and their winters across the sea in the Caribbean and in Central and South America. That is, of course, unless they are migrating.

Migrating thrushes can show up in just about any relatively vegetated environment, and one in particular, Swainson’s Thrush, seems to be quite happy to use suburban backyards while in passage. At times they even seem to let you know how satisfied they are in the trees and shrubs of your yard by singing.

John Schwarz photo

Now if the song of Swainson’s Thrush is familiar to you, then you probably equate that song to deep, shady ravines of northern hardwoods, hemlock, or spruce forests. I know I did. Imagine my surprise upon hearing them in the pecan/hackberry/elm/Bermudagrass habitat that defines my suburban neighborhood.

With their enormous breeding distribution, Swainson’s Thrushes follow a broad migratory front through a lot of the continent where they neither winter nor breed. But because they will use suburban backyards - and because they’ll sing while using them - this bird is perhaps better known to people in the Great Plains than it is to people in the Canadian Shield.

I was struck this spring by the length of time it took Swainson’s Thrushes to pass through my little neighborhood in Stillwater, OK. From about mid April until last Friday, May23rd, I awoke every morning to the lovely song of Swainson’s Thrush in my suburban backyard. At times, I could discern two or three, but usually there was just one. Odds are it wasn’t the same one all that time, but either way it’s interesting. Most birds in spring migration don’t waste a lot of time on their way to breeding grounds, in contrast to “fall” migration in which there’s really no hurry for most species. These thrushes, however, took their own sweet time moving through. And it was fine by me.

All right, let’s not overlook the big one:

“There are no transitional fossils.”

Dr. Steve called this “A flat-out factual galling lie.” There is no way to believe that we have no transitional fossils unless one simply ignores them.

I was once in the American Museum of Natural History when I encountered a group of creationists wandering through the museum and “debunking” all the allusions to evolution. I engaged one of these mental giants who asked me “Why is there no such thing as a half-lizard, half-fish?” I quipped “They’re called amphibians, and there are thousands of them downstairs!”

Just some of the beautiful transitional forms in the fossil record, displaying exactly what evolutionary theory predicts they should . . .

feathered dinosaurs - take your pick, there are probably a half dozen described by now

Australopithecines - upright, fully bipedal apes

“frogamander!”

Tiktaalik - the walking fish

The leggy snake, Eupodophis

And my all-time favorite, Cynognathus. (artwork here by Arthur Weasley.)

Cynognathus was a reptile, or a mammal, or a mammal-like reptile. It’s actually not that easy to say for sure. One the single most important skeletal criteria for defining a fossil as “mammal” or “reptile” is the jaw articulation - what specific bone in the jaw articulates with what specific bone in the skull. In reptiles, it’s the quadrate and the articular. In mammals it’s the dentary and the squamosal.

Several years ago while teaching “Mammalogy”, I studied the jaw arrangement of Cynognathus and came to the conclusion that the quadrate met the articular when the mouth was closed, but when the animal opened up wide, the dentary and squamosal were brought in contact. Hence this transitional animal was a reptile with its mouth closed and a mammal with it open! (It’s a mammal in the image above.)

Now I may not be 100% correct on that last bit, but clearly this endothermic, dog-looking reptile is properly placed at the crotch of the phylogenetic tree where the mammals and reptiles went their separate ways!

. . . And from Skeptical Rogue Jay Novella, the fifth widespread, egregious, ignoramus-breeding misconception about evolution is:

“If evolution were true, then brain cancers should increase brain function.”

This is a paraphrase from a leading proponent of Intelligent Design.

The idea, if one could elevate it to that term, is that evolution advances through mutation, so mutant cells in the brain that suddenly become highly prolific and successful should improve brain activity.

The problem here, in the context of the discussion, is not this specific, moronic statement. This statement is just one that typifies the larger problem of evolution opponents being generally ignorant about what evolution is and what it predicts. There are people making careers out of fighting evolution who have very little understanding of evolution. That is sad, and wrong. If you’re going to invest the time in, say, writing an anti-evolution book, shouldn’t you at least know what it is you’re criticizing?

This is why for the life of me I cannot understand how people cannot see the biological fact of evolution all over the place! The reason is that they don’t know what they’re looking at, and the reason for that boils down to intellectual laziness, if not blind ideology, and I can’t abide by either.

We have Skeptical Rogue Evan Bernstein to thank for this one:

“If humans evolved from apes, then why are there still apes?”

Well, we didn’t evolve from these apes . . .

Evolutionary theory applied to human evolution predicts that humans and extant apes share a common ancestor. We didn’t evolve from them; they didn’t evolve from us; we both evolved from something different, and a long time ago.

Why do we think this? Well, the morphological evidence pointing to a close affinity is overwhelming - we (humans, chimps, gorillas, bonobos, orang-utans, gibbons and their ilk) share many skeletal similarities, similar tooth structure, no tails, ability to stand upright on hind legs, forward facing eyes, five digits with flat nails on each hand/foot, etc.. Behaviorally, there are amazing similarities in communication and long-term social bonds and in the individual’s ability to solve problems. Perhaps most telling, genetic evidence suggests that the vast majority of our DNA can be found in chimps, and vice versa. Next time you see a horse and a donkey, think about the fact that we are probably genetically closer to chimps than horses are to donkeys.

If God made Adam out of clay, then he must have first made the clay out of chimpanzees.

But I digress.

When a new species evolves from an existing or “parent” species, all that means is that two (or more) populations have become reproductively isolated. Where there was formerly gene flow between the populations, there is no longer. Speciation is a fascinating process with never-ending shades of gray and fodder for endless graduate student discussions over cold beer, but all it really means is reproductive isolation among populations.

When a new species develops, the parent species may still exist or it may go extinct. It is entirely possible for something to have evolved from something else, and for the original something to still exist. For example, I’m willing to bet that the Florida Scrub Jay evolved from the Western Scrub Jay.

Florida Scrub Jay, photo by Melody Hendrix

Western Scrub Jay, photo by Carl Erickson

In our case (humans and chimps) however, we did NOT evolve from each other. We shared a common ancestor (one that is no longer with us) about 8 million years ago (Thanks Steve for that figure.)

“We’re all a bunch of cousins; grandpa’s dead.” Rebecca Watson

More genius from the Skeptical Rogues, this one from Dr. Steve Novella:

This one comes in the form of that great story about the softball team who carried the injured opposing team’s player around the field to touch every base after she hit a home run.

Great story. The problem is that the nimrods over at The Discovery Institute have come up with a way to use this story to attack evolutionary theory, namely that the selfless acts of the team who carried the injured player are at odds with predictions from evolutionary theory. What could possibly have been the evolution-based motivation of those players to do such a wonderful thing?

(We’ll forget for the moment the lunacy of comparing a competitive sporting event to lifetime reproductive success . . . )

Steve actually gets us a two-fer out of this one.

1. “Every feature and every behavior of organisms is attributed by scientists to some important selective function, and the silly ‘Darwinists’ concoct these ‘just so’ stories to support their pet theory.”

Wrong again, I’m afraid.

The adaptationists may delight in postulating weird and wonderful ways that selection may have shaped strange features or odd behaviors of organisms, but their work has little to do with the theory itself. Some evolutionary biologists actively eschew the adaptationist line of research.

The reason is that not every trait needs to be selectively advantageous to exist. Some traits are the result of complex genetic linkages or developmental pathways that are influenced by other traits that are advantageous. The only thing a trait has to do to be perpetuated in a population is not reduce rates of survival or reproduction relative to others in the population that lack the trait. If the trait is “benign” then it can be perpetuated even if it conveys no selective advantage whatsoever.

Next comes the notion that . . .

2. “In the struggle for existence, individuals must compete for every resource - cooperation could not evolve.”

Oy vey.

Cooperation, apparent selfless acts, altruism - these are vital survival aspects for social organisms, and we humans are social organisms. There is abundant scientific literature on research that demonstrates benefits to the individual from acting for the good of the group.

Steve groups these two misconceptions about evolution under the heading of unstated major premises, i.e., the idea that someone attacks an idea on grounds that have little or nothing to do with the idea. It’s the same logical fallacy in misconception #1 - that evolution can’t explain the origin of life. It doesn’t attempt to do that, so criticizing the theory on those grounds is silly. It’s kind of like complaining that you don’t like Gone With the Wind because the computer animation was lousy.

Check out Boone Pickens’ latest business venture, if you can handle the irony.

From Skeptical Rogue Bob Novella:

“Evolution is random. How could a random process result in such functional design?”

Evolution is not a random process. Natural selection, by definition (”selection”) involves a most decidedly non-random expansion of some traits in a population relative to others.

The key to understanding selection is that some individuals in a population at any given time will possess heritable traits (e.g., anatomical, physiological, behavioral) that provide an advantage over others in the population. They may resist heat or cold more effectively, have a more efficient digestive system for certain types of food, produce a more nourishing milk, have a natural immunity to some local disease, produce larger clutches of eggs, grow larger and more attractive antlers, communicate their needs and desires more effectively to other members of a social group . . . whatever. The result is, however, that those individuals with the advantage produce more surviving offspring during their lifetime than those at a disadvantage. So long as conditions persist to support those specific advantageous traits, then those traits will increase among members of the population, because it’s the individuals with those traits that are out-pacing the reproductive output of the individuals without those traits.

So where does this “random” notion come from? The ultimate source of variation in traits (the stuff on which selection acts) comes from genetic mutations. Changes in the nucleotide sequences in DNA may result in changes in genes and the proteins built from the genetic blueprint. Many mutations are deleterious, some have negligible influence on lifetime survivorship and reproductive success, and some may confer a selective advantage at a particular time and in a particular place. Those are the ones that get passed on to subsequent generations - the ones that ultimately transform the entire population. This is evolution.

There is design in nature. The process of selection is design. As Bob eloquently states, this design is bottom-up rather than top-down.

Killdeer on its nest. This creature is an example of exquisite design in anatomy, coloration, behavior, etc., all finely tuned to promote maximum lifetime reproductive success as a result of the process of natural selection.

I was listening this morning to my favorite podcast, The Skeptic’s Guide to the Universe. The Skeptical Rogues had a great round-robin discussion on the top five misconceptions about evolutionary theory. I so enjoyed the discussion, I thought it would make great fodder for a five-part series of posts, right here. So here is a paraphrase of misconception #1 from Rebecca Watson.

“Evolution can’t explain the origin of life.”

This one is technically not a misconception because it is, in fact, correct. Evolution cannot explain the origin of life, but this is not a problem or weakness with evolutionary theory, as many detractors from the theory believe. Evolution does not attempt to explain the origin of life. It never has.

Modern evolutionary theory seeks to explain the morphological, ecological, behavioral, physiological, and genetic change in organisms over time, and to construct phylogenetic trees of relatedness among organisms. Living things change over time. Evolution is concerned with the mechanisms and the pathways of those changes. Evolution assumes life is here - it does not specifically attempt to explain the forces that may have occurred for life to develop from non-life.

Abiogenesis attempts to do that. While there have been some tantalyzing descriptions of mechanisms that may explain how life arose on earth, no one theory has garnered universal appeal. Abiogenesis is a dynamic field.

A new report by the Zoological Society of London (summarized here) confirms what natural history advocates have long suspected: we’re losing species, globally and rapidly.

This new report doesn’t focus so much on extinctions, but on the loss of abundance of species. In the period from 1970 - 2005, overall population declines of terrestrial species (25%), marine species (28%), and freshwater species (29%) point to systemic habitat loss and degradation from human land and water uses.

The report includes a calculation of “ecological footprint“, based on the figure of 2.2 global hectares of resources on average needed to support the consumption of each person on earth. The problem is that the earth only has about 1.8 hectares to give. Thus, the lifestyle of the average human is unsustainable - and that’s the average. People in industrialized nations are consuming way more 1.8 hectares worth of Earth’s resources per year. The worst offenders? US, of course. The average American’s ecological footprint is about 9.5 hectares per year. In contrast, the Japanese average just 4.5 hectares and the Chinese about 1.9.

Despite all the complaining about Japanese whaling (some of it right here in this blog!) or Chinese exploitation of rare species for traditional medicines, the greater damage to global biodiversity is being wrought by the suburban American family of four with their 2 cars, 2 children, nice lawn, and their daily rhythm of school and work and soccer practice and church. We don’t take the crushed tiger bone and we don’t eat the whale sushi, but we must own up to the fact that the way we live our lives in this country is every bit as damaging to global biodiversity as those vices. The American Dream is just that, and one day we will be forced to awaken.

To learn more about the ecological footprint concept, go here.

On the last day of the OOS Spring Meeting and Arbuckle/Simpson Nature Festival, TNC’s Jona Tucker led us on a tour of the Pontotoc Ridge Preserve north of Tishomingo, OK. Andy and I didn’t have time to stick around for the whole tour, but we still got to tromp around through a beautiful area of the state with forest, prairie, rock outcrops, and springs all concentrated in this one place. Very nice.

The highlight for me was finding a couple of lingering LeConte’s Sparrows in a tallgrass meadow and getting in close enough for a few mediocre photos. We flushed a Sedge Wren from the same meadow, but strangely, nothing else.

Check out the warm ochre wash of the breat contrasting with the clean, white belly on this bird. At close range, the gray nape with reddish streaks takes on a purplish or mauve color. This is simply a lovely little bird, and all birders in the southern plains should take some time to try and flush them from tallgrass patches in which they might be wintering. I still haven’t encountered them on their breeding grounds, so I’ve never heard one sing. Someday . . .

The bird was doing a rapid wing flick and tail twitch as I worked in closer for a photo.