Last day… were talking about macroevolution…- ended on topic of punctuated equilibrium

Some debate just about frequency of patterns detailsof patterns

Real question – is macroevolution just more natural selection, or something else?

Some versions of P.E. suggest hard to change a species, likely to happen only at speciation

Suggests major trends in evolution are not due to natural selection acting on population, but rather due to species selection

- new species may vary in any direction, but certain types of species may be more likely to speciate again, or less likely to go extinct, & thus create trends

Quite controversial, & not much evidence to support these extensions of P.E. theory?

Punctuated Equilibrium suggests species evolve quickly – current evidence?

e.g. African cichlids- L. Victoria - > 500 endemic spp.

- geological surveys - L. Victoria largely or completely (??) dry ~15,000 years ago - implies numerous speciation events in lake in 15,000

years, & tremendous morphological diversity generated

- appears that ‘species flocks’ are monophyletic groups - suggests that speciation took place in same lake

Genetic evidence suggests that process took longer - start 4 MY to 100,000 years ago? - but much speciation in last 15,000 yrs and still exceptionally fast!

How long do you think it would take for > 500 species to evolve from a common ancestor?

A) 15,000 yearsB) 40,000 yearsC) 4 million yearsD) 15 million yearsE) 40 million years

On other hand: tadpole shrimp (Triops)

- no morphological change since Triassic (>200 MYA)!

Cichlid case an example of adaptive radiation: evolution of many new spp. from a common ancestor when exposed to new environment

Other examples: - Galapagos (Darwin’s) finches – 15 spp.

- Hawaiian honeycreepers – ~32 recent spp. (many extinct)

Iiwi

Akiapolaau

Hawaiian silverswords radiation - 28 spp. in ~5.2 MY

- likely ancestor a tarweed from s. California

Carlquistia muirii

- South American mammals – 75-100 genera in 15-20 million yrs.

Pyrotherium

Toxodon

Doedicurus, a glyptodont

What causes radiations?

Evolutionary novelties

- e.g. wings on insects feedback on flowering plants

- origin of skeletons & exoskeletons change predator-prey relationships

Cloudina

Vacanciesa) colonizing new area- islands or continents

b) extinction of other groups

Mass extinctions an important recurring pattern in fossil record

- about 12 events, marking boundary of many geological periods, & especially eras

Some extinctions ‘all’ of the time (2 - 4.6 families per million years)

Mass extinctions have higher extinction rate (up to 19.3 families per M.Y.)

Extinctions are likely a major source of contingency in evolution (outcome depends on chance events)

Controversy over importance of contingency – if start over from scratch, would results be same?

Much evidence that parts of the story would be the same...Cases of convergent evolution indicate that similar traits

have been favored more than once

Klingon

- Old World & New World vultures- hummingbirds & sunbirds

- crocodiles, phytosaurs, champsosaurs, etc.

May not have produced humans, but some organisms likely to look familiar…

Nile Crocodile

phytosaur

champsosaur

Organisms may converge on particular forms, but is there any consistent direction to evolution?

Not much?

Some trends exhibited by particular taxa, rarely general

e.g. ‘Cope’s rule’ suggests animals increase in size within a lineage

- must be a weak trend from origin of life, but debated on finer scale

- late Cretaceous molluscs: found decreases as frequent as increases

- fossil mammals: new spp. average 9.1% larger than old spp. in same genus- trend may exist in some taxa, but likely weak

If there are trends, it still does not mean that evolution is ‘goal-oriented’- evolution acts by favoring those forms that have a

competitive advantage in particular environment at particular time, NO foresight

Pakicetus

In a population of skunks, some of the skunks are found to have an unusual variation, in that they smell sweet and pleasant instead of the usual terrible smelly defensive odor. A study finds that the new ‘Sweet’ mutation is a dominant allele, and also that 95% of the population is made up of normal ‘stinky’ skunks. If the population is in Hardy-Weinberg equilibrium, what is the frequency of the dominant allele? What is the frequency of heterozygotes?

First – what is the H-W equation?

Second – what does the value (95%) represent?A) p B) qC) p2

D) 2pqE) q2