Download Modelos evolutivos: gradualismo y equilibrio puntuado

MODELOS EVOLUTIVOS:
GRADUALISMO Y EQUILIBRIO
PUNTUADO
“Gradualism", or traditional Darwinian evolution.
Remember, there are THREE MAIN criteria necessary
for evolution to occur via natural selection
GRADUALISMO
Descendencia
Variación
Herencia
Selección
Stephen Jay Gould
Niles Elderigde
EQUILIBRIO PUNTUADO
Natural Selection + additional factors, such as the environment this would best be exemplified by Stephen Jay Gould's and Niles
Elderidge's PUNCTUATED EQUILIBRIUM theory, which holds
that natural selection only works in short spurts amongst long
relatively stable periods of stasis, lasting hundreds of millions of
years, in which species don't change (?).
Evidence for Punctuated Equilibrium: Again, there are
abundant FACTS within the fossil record that evolution in
a manner as proposed by Gould and Elderidge. Actually,
the theory of punctuated equilibrium was first proposed
on the basis of paleontological findings.
Briozos: Metrarabdotus
Cheetham (1986) examinó 1000 fósiles del género.
Usando 46 caracteres morfológicos, Cheetham dibujo un
arbol monofilético conectandolos por medio de los
caracteres:
Briozos: Metrarabdotus
Pequeñoa cambios relativos ocurrieron dentro de las
MORFOESPECIES, mientras que grandes cambios fueron
observados entre las MORFOESPECIES NO se encontraron
ejemplares “intermedios” entre las morfoespecies.
[Jackson y Cheetham (1990, 1994) examinaron 7 especies vivas
de Bryozos del género y confirmaron que las morfoespecies
identificadas difieren significativamente entre ellas en el número
de loci para aloenzimas.]
CAMBIO EVOLUTIVO GRADUAL
Sheldon (19) estudió 3458 ejemplares de 8 linajes de trilobites
trilobites.
Los linajes mostraron un cambio gradual convincentemente
pronunciado: Al principio y al fin de cada linaje podrían ser
clasificados como diferentes especies (y solo en un caso como en
diferente género).
Ambos procesos, Puntualismo y el Gradualismo pueden ocurrir.
Al revisar 58 estudios semejantes , Erwin and Anstey (1995)
concluyeron:
"Paleontological evidence overwhelmingly supports a view that
speciation is sometimes gradual and sometimes punctuated, and that
no one mode characterizes this very complicated process."
Eldredge y Gould argumentaron que “estasis es un dato", el cual
debe jugar un papel más prominente en las explicaciones evolutivas.
Richard Dawkin
Evidence AGAINST Punctuated Equilibrium: As with
Dawkin's point of view, punctuated equilibrium does not
fully explain the reason why we see the sudden
appearance of complexity, nor does it explain the
apparent "directionality" towards complexity.
(2) What explains punctuated evolution?
Why might morphological evolution be rapid around speciation events?
Why might morphological evolution be relatively static during other periods of time?
Eldredge and Gould's (1972) explanation (following Mayr): Peripatric speciation of a small isolated population might lead to rapid changes in a
daughter population (drift), whereas large parental populations remain relatively unchanged.
Gould and Eldredge's (1993) explanation (following Futuyma): Populations are constantly changing, but genetic mixture across populations
prevents sustained differences from accumulating. Speciation "locks up" the changes that a population has undergone.
Alternative explanations??