Transcript Chapter 6

Why Bother?
Bacteria and Viruses
• Asexual reproduction (cloning).
• Evolution is fast, mutations are fast.
• This is great…when you don’t have much to
collect and invest.
• New flu every year.
What if you want to be multicellular?
• Mutations take time to emerge when an
organism needs time to grow or when parents
need to invest in offspring.
– Sexual reproduction introduces instant variation
– However 50% of your genes are lost
– And……
The recombination needs to take place
somewhere.
• Sexual reproduction requires
– The “mating/meeting” of two cells
– The cells could be identical and simply released to
“find each other”
– Better strategy: One cell “stays” put and the other
is the mobile “seeker.”
– This drives differentiation and…
This is why we have…
The “Stayer” and the “Seeker”
(A.K.A. Sexual Dimorphism)
• The stayer doesn’t need to be mobile
• The stayer can accumulate resources to
nourish the “new cell”
• The seeker needs to be mobile
• The seeker needs to compete with other
seekers
The Economics of “Stayer and Seeker”
• The stayer has to invest a lot in the process
and be larger and less mobile
• The stayer will benefit from being choosy
• The seeker has a lower investment and
seekers can outnumber stayers
• The seeker benefits from being fast,
aggressive, and clever
Dimorphic behavior begins here!
(More later.)
Female members of some species retain
the ability to reproduce asexually.
• Why?
– Animals raised in captivity (hammerhead sharks)
– Environmental cue that signals an opportunity for
rapid population growth
Benefits of Sexual Reproduction
• Staying one step ahead of parasites
• Robert Vrijenhouk: Monterey Bay Aquarium
Sexually Dimorphic Behavior
• Some “Whys” are controversial
– Male violence
– Rape
• Some “Whys” make sense
– Childcare (females)
– Jealousy (males)
The “why” that Haunted Darwin