• Fossils

• The Law of Superposition

Consistent with Darwinian model of origins…

Most Primitive

Most Complex

What early scientist is responsible for these two important contributions to evolutionary science?

The first fossilized fish appear buried below the first fossilized amphibians which appear below the first fossilized reptiles which appear below the first fossilized birds and mammals.

Indirect

Transitional fossils are fossils which document the evolutionary change, or transition, of one species into another.

The Mesohippus, Merychippus, and Pliohippus are all thought to be transitional fossils, documenting the evolution of the Eohippus into the modern horse. Perhaps one of the most famous “transitional fossils” of all time was the archaeopteryx, which shows evidence of transitioning between a reptile and a bird.

The second line of fossil evidence for evolution concerns transitional fossils.

What is the difference between indirect and direct evolutionary evidence?

Give an example of direct evidence, and of indirect evidence of evolution.

How can the law of superposition be used with fossil evidence to show that organisms evolve?

Give and example of, and describe how transitional fossils are evidence of evolution.

Science sees structural similarities as evidence that organisms evolved from a common ancestor.Structural features with a common evolutionary origin are called homologous structures.

All vertebrates contain homologous structures, and therefore, come from a common ancestor.

Homologous parts are similar in structure, but may be very different in function.

The body parts of organisms that do not have a common evolutionary origin but are similar in function are called analogous structures.

Analogous parts are very different in structure, but perform similar functions. They are NOT evidence of evolution!

Another type of body feature that suggests an evolutionary relationship is a vestigial structure. These are structures that used to have a

function, but no longer do.

Why is discussion of analogous structures inappropriate when detailing evidence of evolution?

How are homologous structures evidence of evolution?

Give an example of a human vestigial structure, and describe why it is evidence of evolution.

Embryology is the study of organisms in embryonic stages. The embryo is one of the earliest stages of growth and development of both plants and animals.It is the shared features in these vertebrate embryos that suggests evolution from a distant common ancestor.

• a tail posterior to the anus• spinal cord• muscles arranged in bundles• cartilaginous, dorsal notochord (what will become the vertebral column in vertebrates)• Pharyngeal gill slits

Shared Common Features:

The biochemistry (DNA) of a bat is much closer to that of a whale, than that of a bird.Not expected unless bat and whale have a more recent common ancestor than bat and bird, but evolution predicts this. Why?The same technology used to determine paternity can be done to determine shared ancestry.

Bat Whale BirdIn one of the most extensive studies comparing human and chimp DNA, the researchers compared 19.8 million bases. While this sounds like a lot, it still represents slightly less than 1% of the genome. They calculated a mean similarity of 98.77% or 1.23% difference

Because bats and whales are mammals!

Humans can be made temporarily immune to certain diseases by receiving antibodies produced in a horse’s body.

Physiology is the study of mechanical, physical, and biochemical functions of living organisms. Anatomy, of course, studies structures within organisms.

Studying physiological and anatomical similarities, and differences in organisms will tell you how closely they are related. The more similarities they share, the more closely related they are!

What are two shared embryological features among all vertebrates?

Give one example of how shared biochemistry is evidence of relatedness, and can therefore be used as evidence of evolution.

How can comparative anatomy and physiology can be used to show relatedness, and therefore be used as evidence of evolution?

The Hardy-Weinberg model enables us to compare a population's actual genetic structure over time (microevolution) with the genetic structure we would expect if the population were in, what we call, Hardy-Weinberg equilibrium (or not evolving). If allelic frequencies shift at all from one generation to the next, then evolution is occurring.

Hardy-Weinberg Equilibrium maintains five basic assumptions:

3.  mutation is not occurring

Under these conditions it is obvious that evolution would not occur.  There are no mechanisms of evolution acting on the population, so the process cannot happen--the gene pool frequencies will remain unchanged.

5.  natural selection is not occurring

1.  the population is infinitely large, and that genetic drift is not an issue within the population.

4. all mating is totally random

2.  there is no gene flow, or migration in or out of the population

Each of these five are mechanisms by which evolution occurs. Natural Selection is not the ONLY mechanism!

However, since it is highly unlikely that any one of these five conditions, let alone all of them, will happen in the real world, evolution is inevitable.

What are the five basic assumptions that must be in place in order for the Hardy-Weinberg equilibrium to be maintained?

How can we use the Hardy Weinberg as evidence that evolution is occurring?