Hi Syd,
as far as my understanding goes, lyrebirds and all other songbirds are
equally removed from their original common ancestor. That is, no
current species is significantly "older" than another (although
different species may have evolved at different times, each is the same
chronological distance from the common ancestor).
Lyrebirds do have a number of ancestral features (syrinx muscles
etc...), but that doesn't make them more 'primitive', and all other
species more 'advanced'. It's just that the evolutionary pressures on
lyrebirds have been different from those on other groups of songbirds,
and that there has been no selection pressure on the musculature of
their syrinx to cause evolution away from the ancestral condition.
Really, there is no such thing as a primitive or advanced species in the
common, everyday sense of the word. If it helps, it is often better to
think of species (or their characteristics) as ancestral or derived.
The case is often made that evolution tends towards more complexity over
time, and in a general, broad sense, this can be viewed as correct.
However, depending on the evolutionary pressures acting on individuals
within a species, over generations, species may become less complex
through the loss of organs/features. For example, the loss of eyes in
cave-dwelling species. Evolution is not geared towards making organisms
more or less complex. It is just a process that selects for individuals
that have (or lack) features that give them a better chance at surviving
to breed than other individuals. If evolution were progressive and had
an in-built tendency towards increasing complexity, bacteria and
nematodes would be almost impossible to find, instead of being the most
numerous organisms on the planet.
Sorry this is a bit rushed, I'm typing in between classes. I hope it
has helped???
Cheers, Mike
-----Original Message-----
From:
On Behalf Of Syd Curtis
Sent: Thursday, 17 June 2004 11:31 AM
To:
Subject: RFI: Lyrebirds as origin of songbirds
I recently had the pleasure of taking two American visitors to Lamington
National Park for a couple of days. They had come to Australia because
of a particular interest in lyrebirds. After hearing Albert's in
Lamington they were going to Victoria to visit Healesville and
Sherbrooke Forest for Superbs.
I was asked what did I think of the argument that all songbirds
originated in Australia and that the lyrebird is the "oldest" songbird?
Being a lyrebird addict from way back, I like the idea, but that doesn't
make it correct, and I have no expertise in evolution generally or birds
in particular. I did point out that lyrebirds and scrubbirds have fewer
syringeal muscles than the general run of Oscines, and that it seemed to
me that evolution towards a more complex syrinx was more likely than the
reverse. But really, I'm right out of my depth here.
Now I'm intrigued. I'd be most grateful for comment from any
birding-aus experts.
TIA
Syd Curtis in Brisbane.
PS And BTW I also like the idea that flying-foxes (fruit-bats) are
primates that evolved flight rather than bats that became vegetarians.
S
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