
Why Sex? Biologists Find New Explanations - bryanrasmussen
https://www.quantamagazine.org/why-sex-biologists-find-new-explanations-20200423/
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vikramkr
The article really highlights that there's likely not one single explanation
for sex - increasing diversity, decreasing diversity through gene repairs.
Same-sex behaviors potentially being something not just even worth being
selected against, highlighting the "good enough" nature of natural selection
where not everything needs a reason. A good read on the complexity behind
explaining phenomena with natural selection - billions of years or random
chance + selection pressures has no requirement to result in clean, neat, and
easy explanations for complex phenomena.

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itchyjunk
I like how the article starts but I think it got lost a bit in hypothetical
and anecdotes towards the end. Not holding it against the article though. As
the article rightly points out, anything involving sex drags in biases as
well.

I wonder how convergent evolution [0] fits into this? Maybe one form of
reproduction leaves a large niche open for another type of reproduction to
fill in.

Could it be that there was sexual reproduction first and asexual reproduction
came later? We always assume the other way around. But maybe conditions were
initially always stressful and only after conditions improved (I am thinking
of conditions on Earth when these single cells organisms were evolving) did
asexual reproduction start.

Last question, is meiosis and mitosis the only two way to reproduce? I had
never really though about it until now.

[0]
[https://en.wikipedia.org/wiki/Convergent_evolution](https://en.wikipedia.org/wiki/Convergent_evolution)

~~~
Suncho
> Could it be that there was sexual reproduction first and asexual
> reproduction came later?

Unlikely. You can't mate with copies of yourself unless there are already
multiple copies of yourself floating around.

I like the story they present in the article. For simple organisms, it's
fairly inexpensive to let defective individuals die off. As organisms get more
complex, it starts to become more costly to allow defects in the genetic code
to persist. Then it becomes worthwhile to perform "integrity checks" to
correct errors in the data as it's being copied.

If a population of organism is put into an environment conducive to a lot of
data corruption, then the ones who are want to perform these checks are the
ones who end up surviving.

You could imagine that when higher complexity organisms are exposed to high-
stress environments, it would help establish their population's ability to
sexually reproduce. The ones who aren't doing it will tend to die off.

Then as the complexity increases further, the genetic complexity itself can be
a permanent endogenous source of high stress. The organism then loses the
ability to produce asexually because it's no longer needed.

Sexual reproduction promotes genetic complexity because it _allows_ us to
survive while having more complicated genes. The recombination and mixing-and-
matching only helps further the process along.

~~~
Supermancho
> Unlikely. You can't mate with copies of yourself unless there are already
> multiple copies of yourself floating around.

Asexual reproduction doesn't require copies of "yourself". Plants can self
fertilize and they are some of the most complex organisms to do it and you
probably know this.

Can you rephrase that statement?

~~~
sdenton4
I /think/ they're saying that if sexual reproduction came first, you have a
pretty basic problem: where's the second individual that the first sexually
reproducing entity mates with?

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Supermancho
Sexual reproduction can involve an asexual (which would be hemaphroditic)
partner.

~~~
limomium
Why would you evolve the necessary organs to sexually reproduce with your
self, with no one else around?

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Supermancho
Often times sexual organs are multipurpose. It's likely a genetic mutation
that allows for sexual reproduction, as with all structural advances. I might
end up with a functioning probiscus near my gamete sack and if I end up
bumping into my fellow eukaryotes, that's just how it goes.

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reubenswartz
I'm not a biologist, but my understanding is that bacteria are much more
likely to undergo horizontal gene transfer when undress stress. (Particularly
troubling these days for antibiotic resistance.)

Seems like it would be a natural next step for single cell eukaryotes to have
a similar mechanism to fix bad DNA, especially given the much longer genomes
of eukaryotes, which the article discusses without mentioning bacteria.

By the time you get to multicellular creatures, this gets even more important
and leads to males, who pass on only nuclear DNA, and females, who pass one
nuclear and mitochondrial DNA.

~~~
koeng
Eukaryotes don’t really evolve very much on the protein level - their
complexity allows them to mostly evolve on the regulatory level (while
bacteria often still are on the protein level).

Practically, this means that getting proteins from elsewhere isn’t that
selected for, while better regulation is. It’s a complicated subject, but
that’s partially why there is so much “junk” dna in multicellular eukaryotes
(single cellular like yeast are still pretty efficient)

~~~
reubenswartz
My primitive understanding is that the bottleneck for bacterial reproduction
is DNA replication, so there’s a huge incentive to shed unneeded DNA,
especially with mechanisms to get genes back via HGT. Am I right in thinking
that the more efficient chromosome replication in eukaryotes doesn’t penalize
junk dna the same way, so it can just stick around?

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tuan
>> It increases genetic diversity in the pool of offspring. That diversity
could then raise the fitness of future generations by making them stronger,
faster, more resistant to parasites or otherwise more adaptable

Probably off topic, but I didn't know this was not a commonly accepted
explanation. When I went to school (maybe middle school) in Vietnam in the
early 90s, I was taught this. My biology teacher said this explains why
marriage between closed relatives is not recommended because it leads to less
diversity, and a bad gene would have chance to manifest.

~~~
Marsymars
Reproduction between close relatives isn't recommended because of the chance
of offspring getting multiple recessive genes. That's orthogonal to the
genetic diversity benefits from sexual reproduction. (In asexual reproduction,
you don't have to worry about offspring inheriting multiple recessive genes.)

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koeng
C. elegans is a good example of this. They have males and hermaphordites, but
interestingly enough, the ratios of those two from lab and wild strains
differed by quite a bit.

Turns out, in a stable lab environment, hermaphrodites were more efficient.
However, once you started changing the environment populations with males
could always adapt faster.

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jackcosgrove
> Nedelcu and her colleagues found that if you alleviate their physiological
> stress — by providing them with a boost of antioxidants — they don’t have
> sex.

Well that explains a lot.

In all seriousness, I find that the idea in the article raises another
question. If mating can increase individual fitness by sharing something, how
is that explanation of sex different than being a member of a social group?
Social species take the idea even further. Is sex simply the building block
for social behaviors, and more sophisticated adaptations beyond sex are now
available?

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sharadov
This is pretty amazing - the fact that it can be immunity-boosting and slow
age-related brain function. This is an area that needs to be explored further.

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jedimastert
These comments make me sad. I thought the HN community was better than this.

~~~
throwaway6575
HN is notoriously bad at anything related to biology, evolution, and genetics.
It's a combination of this ([https://xkcd.com/1831/](https://xkcd.com/1831/))
and this ([https://xkcd.com/793/](https://xkcd.com/793/)) comic. People there
are also fond of finding a bunch of psychology papers that confirms existing
biases.

There's also a misleading phenomenon where many of the fields whose "experts"
chime in on these questions are called _evolutionary psychology_ or
_behavioral genetics_ , making you think that these fields are related to
biology and enjoy the same methodological standards of rigor as well as the
same consensus from biologists. In reality these fields approach the questions
from _psychology_ , and that one field is known for having a bunch of
practices, biases and motivated reasoning that'd make many a biologist
reluctant to touch it with a ten feet pole.

It's very elegant to see the sleight of hand in action: someone makes a claim
about sex, arguing it's a biological reality, and when challenged backs up
their claim with a psych paper from a field that disguises as one from
biologists and pretends that his claim enjoys a widespread consensus among
actual scientists (as opposed to just psychologists). Hence, the claim isn't
ideologically motivated, _it 's just science_. Beautiful

~~~
daemonk
There is definitely a trend of tech bros 1831'ing biology. While it is very
annoying, I do think we should try to be more charitable in how we respond to
them. It's ultimately a good thing that other people are interested in what we
are doing.

~~~
vikramkr
I agree. Maybe I've just gotten jaded from the usual responses I get when
trying to talk about biology with tech people (where they just assume it's
over their head and want painful analogies to "simplify" it for them) that
it's a bit of a breath of fresh air to see people try to engage with it. Even
if they're wrong, well, so was I about basically everything when I took bio
101. It's a way to have those assumptions challenged and learn more. If they
arent open to it and are operating in bad faith, c'est la vie, peoplle gonna
be like that, but if people are approaching fields they dont know in good
faith, then it's a first step.

~~~
throwaway6575
I mean, people being wrong about biology is ok, the issue is when the
discussion devolves into some of the touchier subjects and suddenly everyone
larps as a scientist. "Do you have citations for that?" "There is a widely
accepted consensus that..." "It's not just my opinion, it's science."

This is very strange because in technology threads where actual experts chime
in, no one acts like that. People share their experiences about using such-
and-such stack, sometimes with very strongly worded and passionate opinions
but never with the pretense of scolarship or "quest for truth". Imagine how
bewildering it'd be if people cited publications from "The Journal of
Serverless Stacks" (IF=1.4) in lieu of experience sharing.

~~~
daemonk
Yes. It takes a lot of time for concepts in biology to sink in and become
interconnected mentally. People who are not in the field tend to think about
concepts in isolation. Tech people also tend to think more
mechanistically/rigidly because they are used to things obeying rules/code.

I agree that it can be annoying when armchair biologists make hollow
arguments. But I also do think that we do share some responsibility to not
turn people off completely or make them dig in harder in their positions.

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econcon
If same sex attraction exists biologically, not as a social construct than
it's possible those genes are select as side effect of smth else that comes
with it. For example, my gay friend is godlike attractive and one girl
literally begged him to marry him in really sick ways and he's ended up
marrying her to make his life easier and also because she was completely
attached and attracted to us just because of how he looked. Few months ago,
they had a kid. Has there been any studies which can shed some light on this,
if gay people are more attractive on average or more intelligent?

~~~
slfnflctd
This is really more of a silly and non-scientific anecdotal pursuit of
probably very little value. That being said, I have heard many women say, "Oh,
he's way too hot to be straight". So I think there is at least some kind of
meme-level support for the idea.

I have also met lots of very wonderful, very gay, quite-less-than-
stereotypically-attractive people who could warm almost any soul with the way
their smiles lit up their faces. For whatever any of that is worth.

------
known

        Sex is good for your heart
        A hug keeps tension away
        Sex can be a stress buster
        Weekly sex might help fend off illness
        People who have sex feel healthier
        Loving support reduces risk of angina and ulcer
    

[https://www.nhs.uk/live-well/sexual-health/benefits-of-
love-...](https://www.nhs.uk/live-well/sexual-health/benefits-of-love-sex-
relationships/)

~~~
jshevek
That quoting style is for code. It is difficult to read on mobile.

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globular-toast
The author fails to mention what is probably the largest downside to sex: an
entire half of the population is completely unable to reproduce. The question
"why do we have sex?" could be restated as "why do males exist?"

Unfortunately the answers to that question trouble some people so it's
difficult to establish the truth. The simple answer comes down to the fact
that a species has to find a balance between maintaining genetic diversity,
which is important for resilience and adaptation, and maintaining a strong
breeding population. Males are there to allow some really wacky variations to
exist that just wouldn't be viable in females. It only takes a tiny handful of
males to take part in reproduction, but it takes essentially all females
(especially considering they are only 50% of the population to begin with).

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msoad
I feel you didn’t read the entire article. They study single gender and
asexual species for exactly that assumption you made

