The Evidence for Evolution
How good is the theory?
There are four main categories of evidence for evolution.
Fossil
Evidence
Embryo
Comparisons
Skeletal
Comparisons
DNA
Comparisons
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 called homologous 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 up
for over 150 years.
Put all together, the evidence for evolution makes
a “family tree” of life on Earth.
A more detailed and accurate map
might look more like this:
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)