ArtificialGrape's Evolution Primer
It is not always clear when members really don't understand the basics of the theory of evolution or when they are intentionally misrepresenting them as some sort of strawman argument. The intent of this article is not to provide some all encompassing intro to evolution (see the Additional Reading section for some recommendations) but perhaps we can at least reach a common understanding of what the theory is and is not.
First, what evolution (descent with modification) is not:In this context, there is one illusion that you must do your level best to escape -- an error to guard against with all due caution. You must not imagine that the bright orbs of our eyes were created purposely, so that we might be able to look before us; that our need to stride ahead determined our equipment with the pliant props of thigh and ankle, set in the firm foundations of our feet; that our lower arms were fitted to stout upper arms, and helpful hands attached at either side, in order that we might do what is needful to sustain life. To interpret these or any other phenomena on these lines is perversely to turn the truth upside down. In fact, nothing in our bodies was born in order that we might be able to use it, but whatever thing is born creates its own use. --Lucretius, circa 80 BCE
- Evolution is not "just a theory". Here is a 10 minute video explaining how the term "theory" is used among scientists.
- Evolution is not a theory of how life first began (nor is it a theory on cosmology).
- Evolution does not claim that man evolved from monkeys or modern apes (nor that cross-pollinating roses could beget a dog).
- Evolution does not occur at the same rate across different species, or at the same rate throughout the history of a species.
- Evolution does not mandate that each species branches off new species.
- Evolution (by natural selection) is not the only mechanism through which species change -- though it is the predominant one.
- Evolution is not moving species towards one ideal species.
- Evolution does not act with foresight.
- Evolution cannot start from scratch, it may only modify an organism's current form.
- Evolution is not random. While individual mutations and gene recombining from mother and father into child DNA may be random, the ultimate results of the modifications that survive are not random.
Now for what evolution is:
- Evolution is the theory that the diversity of life on earth began with a single species that gradually evolved branching off new species, and that natural selection was the mechanism for most of this evolutionary change.
- Evolution is gradual -- substantial changes can require hundreds, thousands or millions of generations.
- Evolution tells us that all species (e.g. humans and ostriches) can be linked back to a common ancestor.
Common ancestry allows for testable predictions about evolution.
- Evolution, at it's core, is natural selection which states that if genetic differences within a species impacts an individual's ability to survive and reproduce, then the next generation will have more of the "favorable" (to survival and reproduction) genes, and fewer copies of the "less favorable" genes. Subsequent generations become better suited to their environment over time as additional favorable mutations are preserved and accumulated while injurious mutations are eliminated. This simple process only requires that genetic variances within a species impact the likelihood of survival and reproduction. The ultimate effect can give the appearance of design, though the changes were accomplished entirely through a natural process.
- Speciation generally occurs when a population becomes separated, reproductively isolated, and begins to diverge. These barriers are commonly geographic such as mountains rise, continents drift, drought splits a large forest into 2 forests with a joining grassland, etc. Once the populations diverge to the extent that they are not exchanging genes, and will no longer interbreed after they are reintroduced, they have become separate species.
Speaking of predictions:
- Archaeopteryx (feathered dinosaur) was found in the fossil record where evolution would have predicted -- 145 million years ago between modern bird fossils from 70 million years ago, and theropod dinosaurs from 200 million years ago.
- Evolution predicted a transition from fish to amphibian, and when in history that would have occurred. There were lobe-finned fish, but no vertebrates 390 million years ago, and there were land vertebrates 360 million years ago. Transitional species would have to occur between this range. Using the theory of evolution Neil Shubin predicted that if there were transitional fossils they should be found in fossils around 375 million years old, and in areas that were freshwater. Studying geological text books the team identified a region of the Canadian arctic. After 5 years of digs they found what has been named Tiktaalik with features between amphibians and earlier lobe-finned fish.
- Marsupials are predominantly found in Australia.
- The oldest marsupial fossils (about 80 million years old) are found in North America.
- Marsupials evolved and spread to the south and were to the tip of South America around 40 million years ago.
- Marsupials were found in Australia around 10 million years later.
- Marsupials in Australia diverged into the 200+ species found there today.
- Question: how did they cross the South Atlantic?
- Theory: we know that before the continents split, South America and Australia were joined by modern Antarctica, so marsupials must have traveled across Antarctica between 30 and 40 million years ago.
- Prediction: marsupial fossils should be found in Antarctica dating to 30-40 million years ago.
- Findings: scientists that traveled on an expedition to Antarctica looking for these fossils found fossils of more than a dozen marsupial species, and the fossils were dated to 35-40 million years ago.
- Humans and apes descended from a common ancestor. Apes originated in Africa. Prediction: earliest hominids would be found in Africa. And they were.