This was supposed to be a BIG event in earth’s history - 400 times bigger than the volcano at Mt St Helens – but the event doesn’t get a lot of mention in the human evolution circles… Or am I missing it?
It should have made that critical bottle neck needed for evolutionary change and wiping out those old Homo genus to make way for modern man.
So is it fact or fiction? (Visualize Far Side cartoon and two Neandethals laughing all the way to the cave.)
Are you driving with your eyes open or are you using The Force? - A. Foley
This is more like stretching available data veeerrrryyyy ffffaaaarrrr…
The Toba eruption was indeed pretty damn big, ad it left a lot of people wondering about possible aftereffects. To go on and say that it led to an evolutionary bottleneck critical for human evolution requires to things to be true:
Large volcanic eruptions have the ability to change climate dramatically for years, leading to the dying off of plant life and the starvation of all creatures higher up the food chain (a la the “nuclear winter” scenario that was a popular topic during the Reagan administration).
Rates of evolutionary change can be accurately determined, and thus the timing of major evolutionary developments can be calculated.
I don’t think anyone would dispute the fact that massive volcanic eruptions have the ability to perturb global weather patterns. How much cooling is a matter of debate. A paper from 1990 sums things up nicely; the general view hasn’t changed much over the past decade:
For the Toba eruption, Sigurdsson suggests that there was a 2-4 degree C drop in average global temperatures, although there’s apparently a problem in trying to separate the effects of the eruption from the glacial conditions that already existed at that time. In my view, if the eruption’s effects can hardly be separated from longer-term climae variability, the “doomsday” scenario that some geologists present (e.g., Mike Rampino of NYU) does not seem very likely. (Side note: Prof. Rampino’s research focus is on mass extinctions and catastrophic events, so he’s not exactly viewing the Toba event with an unbiased eye.)
As for rates of evolution - molecular systematics studies are fascinating with respect to the evolutionary relationships that they can reveal. However, if you want to know when two species diverged in time, and not just on a cladogram, you have to start making assumptions about the average rate of mutation for the genetic markers that you’re using. One can attempt to make reasonable estimates, but it is a huge leap to assume that mutation rates are reliably static over the interval of interest to you.
Another thing… Prof. Rampino and his anthropologist colleague, Stanley Ambrose, have calculated a population crash of Homo down to 10,000 in the aftermath of Toba. I haven’t read their paper, but presumably they are estimating the size of the population based upon maternal lineages (through mitochondrial DNA). However, it is not clear to me whether either scientist has considered all those Homo lineages that could have survived Toba but died out sometime later from other causes.
In sum, the silence you’ve noticed IMHO relates to the huge uncertainties involved.