The components of fitness

AdultsFemales MalesGametes

Survival (viability selection)

Sexual selection (mating success)

Fecundity selection

Gametic selection

Compatibility selection

from Futuyma, p. 369

Zygotes

Parents

When the components of fitness are in conflict...

• sexual selection: female túngara frogs prefer male calls with more “chucks”

• natural selection: bats locate chucking males better than non-chucking males

• sexual selection is stronger—most males chuck

from D.J. Futuyma, Evolutionary Biology, p. 346

The Nature of Natural Selection

natural selection “acts” on individuals, but its consequences

are felt in populations

None of the finches were altered by the drought, they simply survived it or not, based on beak depth

The Nature of Natural Selection

natural selection “acts” on phenotypes, but evolution requires

these phenotypes to be genetically determined

Selection: yes.

Evolution: no.

The Nature of Natural Selection

natural selection is not “forward looking”

Natural selection does not “act” for the good of the

species

valid cases of true altruism are not known to exist

Belding’s ground squirrels make “alarm calls” to warn of attack by weasels,badgers, coyotes, hawks.

This behavior puts the caller at risk, and may benefit unrelated individuals.

Is it altruistic?

If this were a true “altruistic” act, all individuals should call equally.

But instead, females call most often.

from Sherman (1977)

Why? Kin selection.

Since females remain close to the natal burrow, females are surrounded by sisters: they call to benefit close relatives.

Males disperse more and call infrequently, because they are unlikely to be genetically related to others nearby.

from Sherman (1977)

Not so good for the species...

Natural selection “acts” on existing variation—how can it create new traits?

• Mutation provides a constant source of variation for selection to act on

• Selection on “preadaptations” can produce novel traits

Figure 3.18. Artificial selection on corn kernel oil content (from Moose et al. 2004). Continuous selection yielded a range of variation not present in the original plants.

Mutation and recombination supply new variation for selection to act upon, continuously.

Selection produces new traits by modifying existing traits

The Panda’s “thumb”: a modified wrist bone (sesamoid) that varies in the bear family from Futuyma (2005)

from Futuyma (2005)

Preadaptations (or exaptations)

Wings in common murre (Uria aalge) are exaptations for diving

Wings are preadaptations in penguins—modified for swimming. So much that they no longer allow flight!

Selection cannot (usually) replace traits, once lost

History constrains natural selection

Cretaceous Hesperornis,

a marine bird with teeth

to grip fish

Modern birds have lost

teeth—this fish-eating

anhinga makes do

without them

from Futuyma (2005)

Bill serrations serve the

same function in the fish-

eating merganser duck

from Futuyma (2005)

Problems with the Theory of

Evolution by Natural Selection

The Argument from Design

Irreducible complexity

Graded complexity of multicellular eyes

• (a) pigment spot or (b) pigment cup– flatworms,

polychaetes, crabs and shrimp, "lower" vertebrates

– detecting light for orientation and monitoring day length

Optic cup

• narrow aperture (like a “pinhole camera”) probably creates poorly-developed images

• nemerteans, annelids, copepods, archaeogastropods (abalone) and nautiloids (Nautilus)

Lensed eyes

• form complex images

• graded complexity in molluscs: immovable lens in some gastropods

the eye of the pulmonate land snail Helix

• through "camera-like" lens in octopus, squids and cuttlefish

Through the lensed eye of "higher" vertebrates. These form the most complex, high resolution images, in part because the lens can rapidly change shape — it is compressible and served by a fine musculature

The Argument from Design

Irreducible complexity in biochemical systems

An argument for intelligent design

• Michael Behe, author of Darwin’s Black Box (1996): the cilium is a “molecular machine” (1998)– without all its tiny intricate

parts, would not function• “irreducibly complex”• evolution of this structure by

natural selection, bit by bit, is impossible

Chlamydomonas flagellum (© 1998 Gwen Childs, Univ. TX)

Human respiratory tract cilia (© Visuals Unlimited)

Typical cilia and flagella

outer and inner dynein arms bridging peripheral microtubule pairs, a central pair of microtubules, spokes joining central to peripheral pairs

Yet, outer dynein arms, spokes, and central microtubules are missing in the eel sperm flagellum (arrow marks one of the missing dynein arms), still the structure is fully functional. From: Woolley (1997).

– Many other exceptions exist (Miller 1997)

– pf14 mutants of Chlamydomonas lack flagella spokes, but can swim