Re: Why sex?: [why did we lose our fur?]

On Tue, 31 Jan 2006 12:14:16 -0500, "CMSchaum" <cmschaum@xxxxxxxxxxx>
wrote:

>
>"Nicholas" <nmfa@xxxxxxxxxxxxxx> wrote in message 
>news:qFyDf.66193$zt1.36873@xxxxxxxxxxxxxxxxxxxxxxx
>
>>
>> That makes a lot of sense once sexual reproduction occurs, but my
>> dissatisfaction is about the transition from asexual to sexual 
>> reproduction.
>>
>I'm not an expert by any means and someone will correct me if I'm wrong, but 
>aren't the three major reproductive methods pretty consistent with the 
>structure of the organism? I mean, single celled organisms are more likely 
>to be asexual vs multi-celled organisms which are variously sexual, 
>including hermaphroditic (like most plants and some worms), heterogonic 
>(many eusocial insects like bees), and asexual.

The correlary between organismal complexity at a cellular leval and
sexuality works well for metazoans, but really breaks at the single
cell level.  There are plenty of obligately sexual protists living
along side related species that have no apparent sexual phase.  This
suggests that the ancestor to metazoans had seperate sexes.
>
>For species that are capable of both asexual and sexual reproduction they 
>can take advantage of a situation where their numbers are low, food is 
>plentify and there are few predatory influences at a particular time, such 
>as in the spring a species can use asexual reproduction to quickly increase 
>their numbers and later in the year, when their numbers are high, and the 
>environment harsher (less food, more predators) they can use sexual 
>reproduction to take advantage of gene mixing.
>

I keep meaning to take a more in depth look at the ecology of Bdelloid
rotifers, but they are an obligately asexual eukaryote.  And they seem
to be fairly cosmopolitan in their distribution so they can't be
explained as an oddball.  I have a feeling they are doing something
interesting when they do the micronucleus to macronucleus conversion,
but I vagully recall experiments that ruled that out.  

>> Having thought about it a bit since I wrote the original mail my comment
>> about bacteria sharing DNA stuck with me. It seems to me that some
>> adaptation of this mechanism could well provide a starting point for
>> sexual reproduction, but it's difficult to see why this should develop
>> from being of benefit to parent plus asexual children to only being used
>> for producing children. It seems likely, that like certain species
>> today, sexual reproduction only occurred initially when resources were
>> plentiful, but this also has the converse effect of it only coming into
>> effect when selection pressures are weakest. My old university textbooks
>>  cop out on the issue altogether saying there must have been selection
>> pressures but making no attempts to speculate (admittedly they are cell
>> biology rather than ecology).
>>
>
Sex is easier to explain if the enviroment changes rapidly. 


B Miller

.

Relevant Pages

  • Re: Gradual evolution from sex to asex.
    ... the infamous "two-fold cost of sex". ... transitions from sexuality to asexuality. ...
    (talk.origins)
  • Re: Why Sexual reproduction is more popular
    ... I know some evolutionary explanation for advantages ... of sexual reproduction against asexual, ... But there are two features of animal hermaphroditism ... precursor of dioecious sexuality. ...
    (sci.bio.evolution)
  • Re: Why Sexual reproduction is more popular
    ... I know some evolutionary explanation for advantages ... of sexual reproduction against asexual, ... own speculation is that serial hermaphroditism is the evolutionary ... precursor of dioecious sexuality. ...
    (sci.bio.evolution)
  • Re: Announcing A New Unifying Principle of the Evolutionary
    ... >> It consists of one entity per biological species. ... For example, the wolf spirit, or the jackrabbit spirit. ... >> the average fitness of the organisms within its domain. ... which practice sexual reproduction by definition. ...
    (sci.bio.evolution)
  • Re: On the Origin of a Species
    ... of species was created with creatures like us in mind...andclearly...as ... No. There's a great number of fungi which aren't ... but sexual reproduction is common. ... sexuality is the ancestral state of all eukaryotes, ...
    (talk.origins)