Presentation on theme: "The diagram you produced on Page 4 of Cladistics:"— Presentation transcript:
1 The diagram you produced on Page 4 of Cladistics: OG E B A D C-- black eye-- long wing-- wide neck-- long leg-- dark body-- large eye-- thick leg-- wide bodyThe differences in the in-group are explained in 10 steps!Comma separation at one step might be clearer!-- wide wing-- long stingerYour cladogram uses numbered traits…I am doing it this way for a reason…
2 This diagram is based on the same clade critter data… But is not the result of cladistic analysis:OG E B A D C25 Steps!!<-- black eye<-- long leg<-- dark body<-- wide neck<-- thick leg<-- wide body<-- long wing<-- large eye<-- wide wing<-- long stingerWhat concept was used to make this diagram?Scientists reject this diagram because of parsimony…why?
3 This is likely your cladogram from Page 4 of Cladistics OG E B A D C-- black eye-- long wing-- wide neck-- long leg-- dark body-- large eye-- thick leg-- wide body-- wide wing-- long stinger
4 What do we do with the newly-discovered Clade Critter (page 5)? OG E B A D C-- black eye-- long wing-- wide neck-- long leg-- dark body-- large eye-- thick leg-- wide bodyF-- wide wing-- long stinger
5 Is it easier to evolve or to lose a characteristic? There are two possible explanations—which is most parsimonious?OG F B A D C-- darkbodyR-- black eyedark --body-- long wingTwoForwardEvolutions-- wide neck-- dark bodyR-- long leg-- dark body-- large eyeA homoplasy ofparallelism or…convergence-- thick leg-- wide bodyA single evolutionBut two reversals-- dark bodyF-- wide wing-- long stingerIs it easier to evolve or to lose a characteristic?
7 Reptiles are a grade (are paraphyletic) Vertebrate CladeHomeothermy(a homoplasy)Homeotherms are polyphyleticReptiles are a grade (are paraphyletic)
8 Tetrapod limbs are complex Ball joint at girdle (pectoral or pelvic)Proximal segment has one heavy boneHinge joint at elbow or kneeDistal segment has two bones for rotation of hand/footSmall cuboidal bones at wrist and ankle for flexibility of hand/foot positionLong metacarpal/metatarsals for palm/instepPhalanges for the digits (fingers/toes)
9 Tetrapod limbs are stereotypical The complex structures are shared among these tetrapods:AmphibiansReptilesBirdsMammalsConclusion: rather than evolving complex limb form and function separately and identically among all these groups of species (i.e., many homoplasies), the tetrapod leg design evolved just once in a common ancestor (i.e., more parsimonious)
10 Reversal of a complex trait is comparatively parsimonious Forward evolution of a leg requires modification of:BonesMusclesConnectivesVascular PathsNeural PathsReversal of a complex trait is comparatively parsimoniousReversal could be just ONE point mutation in ONE gene that normally puts limb development into motion.Without the first step, the rest does not happen.
11 Tetrapod evolution has been reversed multiple times! Thus, it must be easily done… i.e. is parsimoniousLegless amphibians: caeciliansLegless lizards: glass lizardsAjolote: mole lizardsSnakesSo some gene functioning early in tetrapod development can mutate (become defective), rendering some ancestral species (and its descendants) legless.All the rest of the tetrapod genes that had evolved to make the limbs, are made useless by this one mutation.
13 A photo of parent Caecilian with offspring R635RmqosDI/AAAAAAAANYc/jwcNDv1suD4/flesh+eating+amphibian+caecilians%5B2%5D
14 http://www. unexplained-mysteries This ajolote is a snake that reversed the reversal blocking only pectoral limbs (note: belly scale pattern and limb location)Or it is a lizard that has lost only its pelvic limbs (reversal homoplasy)
15 There are also partial losses: the Boa has vestigial pelvic limbs Of course the alternative interpretation is a partial reversal of loss
16 There are several clear examples of reversals of reversals: This snake has reversed the reversal blocking pectoral limbs
17 This is another verified reversal of a reversal: This snake has reversed the reversal blocking pelvic limbs
18 Of course humans will make false claims! This claim of pectoral limbs is clearly false:This snake is in the act of swallowing a frog, NOT sprouting legs!
19 Is dark body a complex characteristic? There are two possible explanations—which is most parsimonious?OG F B A D C-- darkbodyR-- black eyedark --body-- long wingTwoForwardEvolutions-- wide neck-- dark bodyR-- long leg-- dark body-- large eyeA homoplasy ofparallelism or…convergence-- heavy leg-- wide bodyA single evolutionBut two reversalsF-- dark body-- wide wing-- long tailIs dark body a complex characteristic?Maybe one enzyme!