The Evidence for Evolution How good is the theory?
Key Terms: Common ancestor - Homologous structures - Vestigial structures -
Let’s make a Brain Frame (“showing relationships” style) as we learn about the four main categories of evidence:
Fossil evidence • Fossils are the solidified remains or the imprints of once-living organisms. • There are many different types of fossils (petrified remains, molds and casts, frozen remains, as well as footprints, amber, and caprolites). • Fossils are generally found in sedimentary rock (rock layers formed from buried sediments of sand, dust, mud, soil or other small particles, often at the bottom of water).
Thousands of fossils have been found, and there must be countless more beneath the surface, yet to be discovered.
It is incredibly useful that we can determine the age of fossils, using special techniques. That helps show the evolution of life on Earth over time. • Think of how little we would know of Earth’s history without the fossil record. • Only a very small percentage of living things have ever been “lucky enough” to be fossilized!
This is how the fossil record looks when mapped out. Notice the branching pattern, much like a “tree”
Scientists also use comparative embryology as evidence for evolution. How does this suggest a common ancestor to vertebrates?
Another type of evidence for evolution can be found in comparison of skeletal structures. These are calledhomologous structures. How is this evidence of a common ancestor to vertebrates?
Another interesting bit of evidence are things known as vestigial structures. • Vestigial structures are organs, bones, or other body parts, which no longer seem to have any useful function. • One explanation is that they are “remnant” parts from ancestors to those organisms. • Examples are the useless “limbs” of snakes or whales, or our own appendix and wisdom teeth. • Perhaps these parts were once much more useful?
And finally… (drum roll please)
DNA comparisons! • Comparing DNA of living species today, we can infer how closely related all organisms are. • Strongly supports the fossil record and the “tree of life”. • Has also helped us to properly classify living things.
Your “family” is bigger than you think.Did you know that your DNA is… • …98% similar to chimpanzees, our next closest relative? • …92% similar to a mouse (another vertebrate, even another mammal)? • …44% similar to a fruit fly (an insect, not even a vertebrate, but at least an animal!)? • …26% similar to yeast (a unicellular fungus!!)? • …18% similar to any common weeds in your lawn (plants, for goodness sake!!!)?
So does the evidence for evolution support the theory?Or are there other explanations for the fossil record, or for the DNA patterns, or vestigial structures?
Science welcomes new theories, which might challenge the old theories.But any new theory must have supporting evidence.The theory with the best supporting evidence must hold up under scrutiny.The theory of evolution has held upfor over 150 years.
Put all together, the evidence for evolution makesa “family tree” of life on Earth.
But evolution is not a perfect theory. There are still problems with it. • According to the fossil record, evolution doesn’t always go smoothly. The fossils suggest times of rapid change and other times of little or no change. Why is that? Remember the Cambrian Explosion? What was that all about? • The fossil record has some big gaps. There are actually very few “transitional fossils”, or fossils that are something in between two known body structures. Do we simply need to find more fossils? Or is there another explanation? • And finally, is this theory enough to explain the remarkable diversity of life, from bacteria to humans???
Here is a short video about how we think whales evolved from land mammals, based on the fossil record.Do you really think….?(Click on the image to watch - 7:05)