Vestigiality

humans: wisdom teeth, plica luminaris, arrector pili, etc.

also - cave fish with eye sockets and no eyes, etc.

Direct observation

Observation of the constituent parts: mutation, heredity, and selection

DNA.

homologous genes, observation of beneficial mutations and growing genome.

Atavisms.

humans - tail, extra nipples, etc.

also - horses with extra toes, etc.

levels of (fertile) hybridization (mule, grolar bear, etc.)

Experimentation:

Hypothesis: if evolution, the geologic column, etc. are true, then we might be able to find a transitional fossil between fish and tetrapod in rocks of the right age.

Experiment: Explore rocks of the right age

Observation: Tiktaalik

http://nautil.us/issue/33/attraction/its-a-fishapod

If wolves and dogs belong to the same 'kind', then adaptations/mutations can change: body shape/size, fur color, hearing, sight, sense of smell, intelligence, temperament, dentition, etc., etc.

If that level of change is accepted within a 'kind', then:

isn't Coelacanth the same 'kind' as Eusthenopteron?

isn't Eusthenopteron the same 'kind' as Panderichthys?

isn't Panderichthys the same 'kind' as Tiktaalik?

isn't Tiktaalik the same 'kind' as Acanthostega?

isn't Acanthostega the same 'kind' as Ichthyostega?

isn't Ichthyostega the same 'kind' as Tulerpeton?

If all of the above are true, then Coelacanth is the same 'kind' as Tulerpeton - and a sea animal is the same 'kind' as a land animal.

long term selection experiments: e.g. Fox domestication:

In less than 20 generations, foxes changed to have floppy ears, curly tails, piebald coats, shorter muzzles, rounded skulls, higher seratonin, lower corticosteroid levels, and exhibited barking. ref

comparative biology:

I am thinking of an animal - can you guess which one?

It eats,

breathes,

moves,

poops,

has sex,

sleeps,

produces red and white blood cells,

and can feel fear and pain

It has:

a bilaterally symmetrical body

a head, torso, and appendages

a brain with a memory

eyes that see in color

ears

taste glands

sense of smell

sense of touch

spinal chord

vertebrae

ribs

jaw

teeth

esophagus

stomach

intestines

gonads (testes/ovaries)

kidney

bladder

spleen

liver

pancreas

four chambered heart

skin

well... ? 

Hint: you can even sometimes find them in a school...

It's a fish.

Biogeography - ref, ref