descent with modification

inheritance of acquired characters

variations produced in germplasm

sudden and inheritable changes

Darwin's finches

Mule

Australian Marsupials

Cichlid fishes

i $\rightarrow$ iii $\rightarrow$ iv $\rightarrow$ ii

iv $\rightarrow$ i $\rightarrow$ iii $\rightarrow$ ii

ii $\rightarrow$ iii $\rightarrow$ i $\rightarrow$ iv

ii $\rightarrow$ i $\rightarrow$ iii $\rightarrow$ iv

i - b, ii - c, iii - d, iv - a

i - a, ii - b, iii - d, iv - c

i - c, ii - b, iii -a, iv -d

i - d, ii - c, iii - b, iv -a