Mosaic evolution of characters. Skin, eye and hair color all vary together in humans. Ancestor and descendant are linked by intermediate forms having the same character. Analogous characters are attained by convergent evolution where descendants resemble each other more than they do their respective ancestors. Ancestors are viewed as different but related.
Placentals have a placenta, marsupials a pouch where the immature young finish their development.
These are major characters, should they carry more weight in our assignment of relationship. This leads to the distinction between grade and clade. Treat all characters of equal weight and amass as many character as you can. Enter the characters into a computer that runs an algorithm that gives you a number reflecting the degree of similarity between different taxa. Results plotted in a Phenogram showing evolutionary relationships.