Habilis and erectus: was Re: Louise Leakey talks about humanity's origins
- --- In AAT@yahoogroups.com, "Gerard Michael Burns" <michaelburns@...>
> (forgive the messy way of answering, I'm trying to finish a job)
> m3dodds wrote:Think the conventional biologist view, would be
> > --- In AAT@yahoogroups.com, "Gerard Michael Burns"
> > <michaelburns@> wrote:
> >> m3dodds wrote:
> >>> New findings about year ago found that
> >>> habilis and H.erectus overlapped by
> >>> about 500,000 years ...
> >>> Their co-existence in the same area of
> >>> east Africa, living side by side
> >>> probably rules out the habilis as
> >>> an ancestor of H.erectus ...
> >> I have to point out that this conclusion is not
> >> entirely solid. If the two species occupied different
> >> niches, even if geographically coincident, an
> >> ancestral species might continue indefinitely
> >> alongside a species that was derived from it.
> > Fair point ...
> > But in your example, wouldn't the original
> > habilis be said to be 'extinct', and in its
> > place you would have two new species ...
> > habilis( mark II ) and H.erectus ...
> If both groups moved into new niches, both would be
> subject to new adaptive pressures, but if one stayed
> in its old niche (the one to which the ancestor
> species is presumably well adapted), it would presumably
> change little over time. Obviously there are a number
> of species that haven't changed much in millions of years
> although, as I think about it, I'm not sure what the
> oldest 'unchanged' mammals would be.
that there are 'two' new species after speciation
on the premise the 'ancestor' species is still
subject to evolution ... but I may be wrong.
Apparently it goes something like this ...
'A'(ancestor) becomes 'B' an 'C'(new)
An if 'B' the ancestor species, continues, it
will (would) not be the same species that 'C'
split from ...
IMO it would just be simpler to say 'A' is
the LCA of 'B' an 'C' ...
So we could say that the habilis and H.erectus
being sister species probably had a LCA, some
two million years ago. ( only if H.erectus, has
African origins ... the answer will be different
if H.erectus originated in Asia ).
Possibly elephants, manatees and tree sloths would
qualify as the least changed mammals ...
For fast track speciation, possibly Darwin's finches
an a species of fish in east African lakes ... would
Sharks, the oldest unchanged species?
> >> If, for instance, the group within an ancestor speciesThink nature would punish those, that attempt to
> >> were a terrestrial gatherer/scavenger, and then one
> >> band began diving for clams (or chasing herds of ungulates
> >> for that matter), the new group would have very different
> >> drivers of evolution, and could speciate. As long as the
> >> two groups retained their different lifestyles, their
> >> different needs for survival and different prorities in
> >> mate selection would drive them ever further apart.
> >> If we taught baboons to gather clams at the beach, and to
> >> wade into the water for them, there could easily be a
> >> population of water-adapted baboons some thousands of
> >> years from now living only miles from other baboons that
> >> had not changed at all (the aquatic adaptations would
> >> probably be weaknesses in savanna dwellers, and vice
> >> versa, so nature would punish mixing).
> > Wouldn't a 'new' survival/foraging strategy, mean
> > a 'new' species or sub-species.
> > (example: Macaques)
> If a strategy that was facilitated by evolutionary change
> is so useful that the change is more useful than staying
> the same, change would be likely, and speciation would be
> likely if there were either geographical barriers _or_
> conflicts in the capabilities if a better diver is a
> worse runner, then nature would tend to punish mixing.
cross the barrier once the tipping point for
speciation has been reached ...
> In theory, a matrix could be set up that cross-checkedOnce the tipping point is reached, that's it, no
> the value of an evolutionary adaptation compared to its
> cost (if any) to previous capabilities. Obviously, plugging
> values into such a matrix would require God-like foresight,
> but that is the structure to think of. If a new adaptation
> brings in 10 tons of food a year, but costs 10 tons of equally
> valuable food, nothing is likely to happen. Note that if
> the old niche is _overexploited_ then the cost of losing old
> capabilities is less than the 'laboratory value', because
> it is not real (the old food isn't really available anyway,
> so instead off 10 vs.10, maybe it is 10 vs 2). So in some
> cases speciation could occur even when the habitat looks
> friendly to the old behavior.
> > Geographically separated ...Basically we could say, it is when things tip in
> > separate species?
> If there is _no conflict_ between new adaptations and
> the old behavior there is a greater chance of newly
> evolved capabilities simply becoming normal within the
> whole species unless geographical separation exists.
> I am sure speciation does involve geographical barriers
> -of course geographical barriers are rarely perfect,
> so you can have a 'long lost cousin' show up and no
> longer be recognized as conspecific for mating purposes,
> at which point speciation could continue.
> Michael Burns
favour of speciation, an if the 'long lost cousin'
happens to turn up afterwards he or she's no
longer counts as a 'family member' ...
> >> The mere continued existence of the ancestral population
> >> (following the ancestral strategy) does not mean that
> >> the new ones (following a new strategy to which they
> >> have evolved adaptations) did not come from earlier
> >> members of the ancestral species.
> >> Michael Burns
- DDeden wrote:
> --- In AAT@yahoogroups.com, "Gerard Michael Burns" <michaelburns@...>I agree that allopatric (spatial barrier induced) speciation is probably the
>> DDeden wrote:
>>> --- In AAT@yahoogroups.com, "Gerard Michael Burns" <michaelburns@>
>>>> DDeden wrote:
>>>>> --- In AAT@yahoogroups.com, "m3dodds" <dons3148@> wrote:
>> Nonetheless, I do think that spatial barriers are usually key. I just
>> maintain that speciation without real barriers should also be
> possible, and
>> there are examples that seem to support this. Note that I don't think
>> "allopatric" should be used when the distances or obstacles are only
>> the normal ones between group territories, nesting areas, or the
> I've no idea if non-spatial speciation occurs, I only know that it
> would not follow the typical pattern. Geo-spatial separation +
> temporal period in which genetic mutations occur and are selected for
> improved adaptation to local environment -> speciation.
norm. I only maintain that it is necessary not to forget that this type of
atypical event can occur, and may at times be of lasting importance.
> So for example, hypothetically Hh on one side of the water-filledThis is a fair depicton of the allopatric mechanism. Of course the pioneers
> Rift, a pregnant female accidentally crosses to the other side (where
> there are no specialized predators on Hh), begins new generation with
> slightly different traits, with no further mixing they speciate into
> Hh & He, although bones from both may get washed downstream. Since
> the Hh side is stable (predators and environment remain as before), Hh
> doesn't change much. OTOH the He side changes due to slightly
> different milieu/predators/sociodynamics, so stronger selection for
> different mutations. Add a million years, and end up with 2 species
> which may or may not be able to functionally reproduce a healthy
> hybrid if mixed.
entering a new milieu might usually be a group rather than individuals; the
chances of an individual surviving and founding a breeding population which
can then evolve has to be close to impossible.
Not wanting to complicate the matter, but it should be mentioned here that
it seems to be common to find birds which occupy the same geographic area,
and which have long been classified as different species or subspecies, but
which have turned out to be perfectly interfertile, and which nonetheless
hybridize only very exceptionally in nature. This is attributed to different
mating protocols, and is probably due (at least in most cases) to some
long-ago barrier that was overcome after the mating protocols had changed.
This has sometimes frustrated ornithologists.
To get back to the He - Hh dilemna, some isolated group of Hh may have
evolved to He and then, as you lay out, re-crossed the barrier to become
common in the original Hh environment, and, again as you mention, they may
or may not hybridize (apparently did not in the real case), and that can
lead to two closely related species sharing an environment. It is even
possible, however, that like many "species" of birds, they were actually
interfertile but had different mating protocols that excluded each other
from the pool.
That latter mechanism of excluding potential mates for trivial reasons (ones
that would not really affect fitness) would be somewhat counter-survival if
there were no conflict of any kind between the fitness of each in that
environment. However, a conflict in actual basic survival capabilities might
exist that is not visible in the record. Such a conflict could be biological
(a half-cursor/half-diiver on the savanna would fail to compete with a
similar 100% cursor), but could also be cultural. If I had taken up
subsistence farming in the countryside here when I came, both myself and my
children might not have been able to make up for the lack of the kind of
relevant knowledge passed down by fathers who grew up in families that had
been farming for countless generations.