

A Surprise for Evolution in Giant Tree of Life - treefire86
https://www.quantamagazine.org/20150505-a-surprise-for-evolution-in-giant-tree-of-life/

======
alexvr
Isn't this obvious to anyone who takes a little time to think about evolution
and biodiversity? Yes, little changes caused by chance persist if they don't
hinder the creature's ability to survive & reproduce. And these relatively
benign mutations can accumulate until one family is very different from one
that was once more obviously related. I don't see how this "surprising" and
"provocative" proposal that chance plays a role in biodiversity is at all
"controversial" or even new. What's more, the journalist seems to think that
this "finding" means she can downplay natural selection, when in fact this
article should really be nothing more than an emphasis of the role of chance
in speciation since natural selection is basically predicated on the
biodiversity caused by chance mutations. This really seems like publishing
something 100 years after the first airplane was built to say: "Hear ye!
Amazing new finding: In the absence of wings or power, an airplane simply
falls due to gravity!" Maybe the actual research/paper is of more merit than
the article suggests?

~~~
colin_mccabe
In the 1950s, nobody would have believed that "genetic drift" happened at all.
The reason was because back then, the thinking was that any genetic change
must be adaptive and caused by natural selection. The accumulation of
"neutral" changes-- genetic drift-- was very controversial when it was first
proposed, and wasn't really widely accepted until at least the 1980s or 1990s.

This main thrust of this paper seems to be the idea that genetic drift is the
primary driver of speciation (the process of creating new species.) The paper
also makes claims about a "speciation clock" that seems to tick every 2
million years, for many different species.

These two claims seem somewhat at odds. Presumably genetic drift will happen
more rapidly in species like fruit flies or beetles that have short generation
times. Genetic drift should be slow in species like whales since they take so
long to reproduce, and drift can't happen except during reproduction. So if
species are splitting off every 2 million years for both whales and fruit
flies, that suggests genetic drift can't be the only factor, since it's 1000x
faster (or more) in fruit flies as in whales. Anyway, I didn't read the paper
that closely, so maybe I'm missing something.

In general, speciation is a complicated and poorly understood topic with a lot
of controversies remaining. For example, is it more common for a species to
split into two because of a physical obstruction (body of water, mountain
range, etc.), or because different sub-populations start occupying different
ecological niches due to slightly different environments, and gradually grow
more distinct? (allopatric speciation versus parapatric speciation). It's hard
to actually measure how much mixing there was between populations millions of
years ago, so this is still controversial. And parapatric speciation gives
more weight to natural selection so it used to be the preferred explanation.
But this is far from a settled debate.

~~~
mohawk
Just look at those graphs of distributions for speciation times. Reading the
description of the "speciation clock", i would have imagined a sharp
distribution with a very tall peak at 2 million years. Yes, the mode is about
2 million years. But the distribution is veeery broad. Looking at the graphs,
there is no reason to believe that whales and flies have similar speciation
times. A very misleading description, unfortunately quite typical of the
scientific news cycle.

------
DanAndersen
It makes sense that simple historical happenstance is the cause of much
speciation. When learning about evolution and natural selection, we hear so
much about nice-sounding stories about Species X and how they got some
particular Adaptation Y because it allowed them to be more fit in some
particular way Z. While these are likely true, they run the risk of being
just-so evolutionary psychology stories that are told not because they are
_representative_ of mutations and adaptations, but because they are
_illustrative_ of the concept.

There are about 400,000 known species of beetle, some of which are extremely
similar. For how many of them can we point to a cause-and-effect meaningful-
to-humans story of why they have diverged from their closest relative?

Sometimes weirdness just happens and circumstance leads to change.

------
Aloha
Natural Selection however is the process that chooses one random mutation to
succeed over the existing line, or another slightly less advantageous random
mutation.

------
mrfusion
I thought speciation happened due to chromosome fusion/fission?

