A scientific theory is an explanation of nature that has been tested and confirmed repeatedly, that predicts successfully, and that places facts and laws into a larger context to help us understand and make new predictions.
The theory of evolution is highly reliable and useful, not tentative and uncertain.
Easy Come, Easy Go--How Evolution Works
Parents reproduce by having kids.
Kids include experiments introduced during reproduction—the kids are not identical to their parents.
These differences often affect the ability of the kids to survive to have their own kids. This leads to natural selection - the kids with differences that favor survival tend to survive to have kids.
But, despite the differences, kids are quite similar to their parents—the kids just receive a bit more or less of what makes their parents biologically successful.
These processes acting over time give evolution—successful experiments accumulate in new generations, and unsuccessful ones are eliminated so that new generations slowly become different from older ones.
Changes to living organisms are not passed on (if you get a tattoo, your kids will not be born with tattoos)—but the reproductive experiments are passed on.
Major changes must occur slowly over many generations, often thousands or more, to maintain “back-compatibility” — everything in a living organism needs to work together, so huge jumps do not succeed.
Thousands of generations or more require a lot of time for large animals but can occur in less than a year for disease organisms.
The Unbroken Chain
The Law of Faunal Succession that we met in Module 9 suggests that evolution has occurred.
Evolution predicts gradual changes over time, and thus the occurrence of transitional forms, whereas other hypotheses such as special creation or catastrophism predict that there will not be transitions.
Transitional forms have been found, strongly supporting evolution:
Transitional forms are common in commonly fossilized types.
And less common in less-commonly-fossilized types.
Transitional forms are found as often as evolution predicts, and the fossil record disproves competing hypotheses.
Transitional forms are not found everywhere for every species in the fossil record, in part because new species often evolved geologically rapidly from small populations in isolated places (it is easier for a smaller group to evolve).
Taking Care of Business
The theory of evolution is explanatory, predictive, and useful.
Germs are evolving antibiotic resistance, and the scientists trying to keep us alive are using knowledge of evolution to fight those germs.
Computer scientists mimic evolution to solve complex problems (evolutionary computing).
Teach the Conflict?
Scientifically, there is no conflict to teach—there is much to learn and do, but with no serious problems or competitors to our understanding of evolution.
In particular, evolution is:
Consistent with the second law of thermodynamics, and all other known physical laws,
Strongly supported by the fossil record and age dating,
Not anti-religion (indeed, it is supported by many religious groups).
There is widespread and very strong scientific consensus that so-called competitors (e.g., “intelligent design”) are not science.
Thus, “teaching the conflict” would require teaching non-science in science classes (but note that some groups, at some times, have tried to do just that).
Extinction Can Ruin Your Whole Day
There has been a slow "background" rate of extinction, with species being lost about as often as new species appeared during most of geologic history (populations fluctuate up and down and sometimes hit zero, which is extinction).
Occasionally there were mass extinctions when species became extinct much more rapidly than new species arose, but these mass extinctions were followed by millions of years when new species arose slightly more rapidly than old species became extinct, thus restoring biodiversity over millions of years.
Major extinctions included:
the end-Paleozoic mass extinction: volcanic CO2 drove extreme global warming.
the end-Mesozoic mass extinction: a meteorite triggered immense changes in climate
a few others that we won't make you learn in detail, that mostly were caused by large volcanic releases of CO2 that drove heating, loss of oxygen in the ocean, and other changes (note that the modern CO2 rise is unequivocally from humans, not from volcanoes, as we will see in Module 12).
The dinosaurs were doing just fine until killed by changes triggered by a meteorite impact (and, some dinosaurs that were ancestors of modern birds did survive).
The death of all of the non-bird dinosaurs freed ecological jobs (“niches”), allowing evolution to produce large mammals over the 65 million years between the meteorite and us.
The Dinosaur Killing Meteorite of 65 Million Years Ago
Evidence: the geologic record of the extinction event occurs with an odd sedimentary layer containing much iridium (common in meteorites, otherwise rare on Earth), soot from wildfires, high-pressure shocked quartz, droplets of melted and then rapidly frozen rocks, a giant-wave deposit in places near the Yucatan including the Caribbean, and a giant crater of the right age on the Yucatan Peninsula.
Mechanisms: the meteorite blasted things up, causing a fire from the heat when those things fell back to Earth, then cold and dark, from the sun-blocking effect of slow-falling things that also had been blasted up, with acid rain and then heating from CO2 released from the sulfate and carbonate rocks where the meteorite hit.
A thought: there still are big rocks out there in space—averaged over millions of years (and presuming we humans hang around that long), they are likely to kill as many people as commercial airline crashes, but not nearly so many as car crashes, and we can reduce the dangers from airline crashes and car crashes.