26 May ’07
The missing fossile link
If I remember correctly, one of the criticisms on the evolution theory, is the gaps in the fossile record. There has long been a search for fossiles of ape-men, and of other in-between species (reptiles and mammals, for example). With my understanding and knowledge of biological experiments on the evolution of species expanding, I wonder if this gap has not yet been closed.. not by finding fossiles (which may have well occurred with me being unaware of it), but by the observation that evolution isn't the slooooooooooooow process people expect it to be.
It is slow. It must be. One of the best documented species on the planet, -us-, hasn't changed dramatically in the last 2000-4000 years, now has it? Well, you might argue that we've increased a decent amount in size (although that is not completely accurate), came to live quite a bit longer, and are currently evolving into a weightier species.
Our own example might not neccesarily be a good indication of the general speed by which species evolve. While it may be a tough world out there, the human race is in general not under a high selection pressure (and our strong culture might have even turned some biological rules upside down), and selection pressure might be one of the driving forces behind speciation (I'll have to read this article to check if I'm not falling into some logical trap, and will summarize it afterwards).
For our own species, selection of the fittest is becoming a complicated matter, and thus the rules of evolution for humankind might not be the same as those for naturally living animals. In humans, no longer do those humans that in our western eyes are 'the fittest' produce the most offspring: population numbers in europe and the western world are on a decline, whereas third world nations have a higher growthrate (UN report, table 3).
Returning to animals. If I remember the chiclide stories of the Victiora Lake in africa well, then these fish were very quick to evolve into new species by diversifying mating and feeding habits. These fish have the remarkable property of being very plastic in their phenotype: a few changes in gene expression or gene duplication could cause a large differntiation on phenotype (the physical appearance) of these fish, allowing for quick speciation.
Here is the theory. If speciation happens almost exclusively in situations when there is a large amount of selection pressure, and for that reason happens way faster then the 'rate of change' we observe in static species.. then we might be overestimating the number of 'in between-fossiles' that should be found based on probability. If between 40.000 years of humanity (~1600 generations) and 200.000 years of chimp-like animals (~40.000 generations) (I'll have to find some refs for these estimates) there were 10 generations of 'large changes' - in which we straightened up, lost our fur, altered out feet to a less handlike variant.. then the odds of finding a fossile of a small group of apes that went out of the forest to do something different, amidst a large group of apes that did not, over a period of 250 years before they small group of apes looked human enough (phenotypic plasticity).. well. the feeling is that those odds aren't good.
Not sure if it is an alternative to 'selection pressure', or just a different description, but if a species ends up in an environment that it is not adapted for, then the above might also apply.
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Alternative options to the 'slim chance', or perhaps contributing options is the 'neutral net' theory of mutations. The theory states that within a population, there can be considerable genetic differences between species, while phenotypically they still function and look the same. In this population with a wide genetic spread, some of the members might be only a few mutations away from making a large phenotypic change. I'll expand this bit later, or leave it out entirely.. depends on what fits the story.