Sexual and Asexual
Reproduction
Making More Organisms
In evolution, reproduction is the bottom line
In a basic sense, the most important thing an organism can do
(evolutionarily) is reproduce.
-If it doesn’t reproduce, it doesn’t pass on its genes and it has no effect
on the future of the species.
-The more offspring an organism has, the bigger the impact it has on
the future of the species.
-Because of this, those organisms that were best at passing on their
genes are the ones that are most represented now.
So why not live forever?
“Well, obviously because we get old.”
What IS aging?
We aren’t entirely sure. There are a few
theories:
1) Telomeres wear down.
2) Oxidative damage builds up
3) Adaptation?
1) Telomeres wear down
Telomeres are protective “caps” at the ends of our DNA. Every time
our DNA divides we lose a little bit of them. After a certain number of
divisions we simply run out of telomeres and we start losing pieces of
“real” DNA.
2) Oxidative damage builds up
Throughout our lives our cells take damage from reactive chemicals
(“free radicals”). Over time this just wears them down and they stop
functioning.
3) Death is an adaptation
It might actually be better to live fast and die young IF you can produce
more offspring because of it.
It’s like asking whether it’s better to
have a guaranteed payoff now or a
possible payoff in the future.
This is probably why organisms don’t
live forever: it’s a bad investment.
In summary:
BECAUSE: Living forever is either impossible or not a very good idea
THEREFORE: Organisms have to reproduce
BECAUSE: The only way organisms can affect the future of their species is
reproduction
THEREFORE: You can tell what organisms were good in the past by what a
species looks like today
BECAUSE: The organisms that reproduce the most add the most to the future
of the species
THEREFORE: “Winning” the game of life is having the most offspring
Two types of reproduction
Sexual and asexual reproduction
Sexual reproduction
• Involves two parents
• Mixes the DNA of both parents
Pros:
-Creates lots of variation
-Can create better offspring
Cons:
-Slower
-Can create worse offspring
-Have to find a mate
Our friends again…
Sometimes it doesn’t turn out so well…
Asexual reproduction
• Only one parent
• Creates a single clone of the parent
Pros:
-Faster
-If the parent works, so will
the offspring
Cons:
-Not good for adapting
Organisms that (can) asexually reproduce
Some organisms can choose
When might it be best to sexually reproduce?
When might it be best to asexually reproduce?