ELABORATED MALE TRAITS MAY BE INDICATORS OF HERITABLE GENETIC QUALITY (I.E. FITNESS). GOOD GENES MODEL The Handicap Principle (Zahavi 1975) Some males may have a heritable trait that reduces viability. Only males with Good Genes can survive despite the handicap. Females that mate with these males will have offspring with higher fitness.

HANDICAP PRINCIPLE The bigger the handicap, the higher the genetic quality of the male carrying the trait. Female choice evolves and the handicap spreads and becomes elaborated. This is an example of an honest signal since there is a true cost to the elaborated trait that prevents cheaters.

FISHERIAN RUNAWAY SEXUAL SELECTION An alternative to the Good Genes Hypothesis: Assortative mating within a population between males with the most exaggerated trait and females with the strongest preference can lead to a genetic correlation between trait genes and preference genes. The female preference genes will hitchhike onto the successful male genes.

Fisher's principle An evolutionary model that explains why the sex ratio of most sexual species is approximately 1:1. It was famously outlined by Ronald Fisher in his 1930 book The Genetical Theory of Natural Selection (but incorrectly attributed to Fisher as original. Fisher couched his argument in terms of parental expenditure, and predicted that parental expenditure on both sexes should be equal. Sex ratios that are 1:1 are hence known as "Fisherian", and those that are not 1:1 are "non- Fisherian" or "extraordinary" and occur because they break the assumptions made in Fisher's model.

Condition that males and females cost equal amounts to produce Suppose male births are less common than female. A newborn male then has better mating prospects than a newborn female, and therefore can expect to have more offspring. Therefore parents genetically disposed to produce males tend to have more than average numbers of grandchildren born to them. Therefore the genes for male-producing tendencies spread, and male births become more common. As the 1:1 sex ratio is approached, the advantage associated with producing males dies away. The same reasoning holds if females are substituted for males throughout. Therefore 1:1 is the equilibrium ratio.

Suppose that males with longer tails are preferred at first because they have higher viability (Good Genes). The increased reproductive success of these males increases the frequency of trait and preference genes and reinforces assortative mating since offspring carry genes for both exaggerated tail length and strong preference. When there is a genetic correlation between the male trait and female preference then the process becomes self-reinforcing. FISHERIAN RUNAWAY SEXUAL SELECTION

FISHERIAN RUNAWAY CAN LEAD TO MALADAPTIVE TRAITS When the trait and the preference are genetically correlated, then the trait can evolve way beyond the point where it indicates overall genetic quality. Runaway of the male trait can proceed to a point of exaggeration where it actually decreases male fitness. The runaway process leads to a situation where the only benefit to female choice is that her sons inherit the most attractive state of the trait. This is in direct contrast to the Good Genes Hypothesis and has been referred to as the Sexy-son Hypothesis.

Evidence for a genetic correlation between trait and preference from Three-spine Sticklebacks.

EXPERIMENTAL EVIDENCE FOR FISHERS RUNAWAY PROCESS Stalk-eyed Flies have heritable variation for the distance between eyes in males and for female preference for stalk length Short Stalk Long Stalk

ASSORTATIVE MATING AND THE DEVELOPMENT OF A GENETIC CORRELATION BETWEEN TRAIT AND PREFERENCE

EVIDENCE FOR A GENETIC CORRELATION BEWEEN TRAIT AND PREFERENCE

RESULTS OF SELECTION EXPERIMENTS

FROM: Faivre et al. Science. April 4, 2003 Immune Activation Rapidly Mirrored in a Secondary Sexual Trait A crucial assumption underlying most models of sexual selection is that sexual advertisements honestly reflect the phenotypic and/or genetic quality of their bearers. Here we show that experimental activation of the immune system is rapidly mirrored in the expression of a carotenoid-based secondary sexual trait in male blackbirds (Turdus merula).

Carotenoid Modulation of Immune Function and Sexual Attractiveness in Zebra Finches Blount et al. One hypothesis for why females in many animal species frequently prefer to mate with the most elaborately ornamented males predicts that availability of carotenoid pigments is a potentially limiting factor for both ornament expression and immune function. An implicit assumption of this hypothesis is that males that can afford to produce more elaborate carotenoid-dependent displays must be healthier individuals with superior immunocompetence… In this study, we show that manipulation of dietary carotenoid supply invokes parallel changes in cell-mediated immune function and sexual attractiveness in male zebra finches (Taeniopygia guttata). SCIENCE, April 4, 2003 Experimental Group Control Group

ALTERNATIVE HYPOTHESIS FOR THE ORIGIN OF FEMALE PREFERENCE Sensory Bias (Ryan) Preexisting preferences for certain traits may be hardwired in females and lead to the development of exaggerated traits in males.

EXAMPLE OF SENSORY BIAS IN TRINIDAD GUPPIES Female guppies are attracted to ORANGE. This response may be due to feeding behavior selecting for the ability to locate ripe fruit. Sexual selection then favors males with lots of orange working on a preference that is already in place.

PHYLOGENETIC PREDICTIONS OF THE OF SENSORY BIAS HYPOTHESIS P+/T+P+/T+ P+/T+P+/T+ P+/T-P+/T- P - /T - Female preference should evolve first, followed by the evolution of the male trait. FEMALE PREFERENCE MALE TRAIT

Females of species in the genus Xiphoporus in which males do not have swords PREFER males with swords. The primitive condition is for male to have no swords. Swordtail EVIDENCE FOR SENSORY BIAS

The Theory of Recapitulation The theory of recapitulation, also called the biogenetic law or embryological parallelism often expressed in Ernst Haeckel's phrase "ontogeny recapitulates phylogeny"is a largely discredited biological hypothesis that in developing from embryo to adult, animals go through stages resembling or representing...

Haeckels Recapitulation Theory Ontogeny recapitulates phylogeny An individual organisms biological development (ontogeny) parallels and summarizes the evolutionary development of the species (phylogeny) Theory has been discredited since the early 20th century. While ontogeny and phylogeny are closely related and intertwined, there is by no means a one-to-one relationship between them.

Haeckels Artistic Pursuits

Embryo Fraud Unfortunately, Haeckel used his artistic talents to strengthen his arguments for common ancestry He subtly changed aspects of embryos to reflect his theories Though he confessed to having fudged the drawings during his lifetime, the confession was lost and his embryonic drawings were newly discredited within the last 20 years

Other Controversies Haeckel attempted to create a genealogical tree reflecting a hierarchy of human races, placing white Europeans above many other races His theories were used by the Nazi party to confirm their belief in Aryan supremacy after his death