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Posts Tagged ‘evolution’

Was Darwin overrated?

In Biology on February 15, 2009 at 2:06 am

Watch John Horgan and Carl Zimmer, preeminent science journalists, gab about Darwin (his birthday was Thursday.) Darwin as Hollywood star, horizontal evolution, rethinking the tree of life, group selection — it’s all good.

As for whether Darwin is overrated, there are a couple ways of looking at it. You can focus on his contemporaries and predecessors, and note that he wasn’t alone in thinking about evolution: there was traveling naturalist Alfred Russel Wallace, whose observations about the geographic distribution of species led him to theorize about the divergence of species, and whose correspondence heavily influenced Darwin’s Origin of Species. The idea that species change over time was advanced by Robert Grant, who saw a progression in fossil animals; Robert Chambers, author of the popular-science bestseller Vestiges of the Natural History of Creation; and Charles’ grandfather Erasmus Darwin, who hypothesized that all life had a common origin. You could argue that Darwin worked in a ferment of ideas about life’s origins and variation, that he was not alone. It’s a useful perspective. Scientists are rarely lone geniuses, even if they are geniuses — they collaborate, borrow, and bicker like everybody else.

Does that make Darwin overrated? I don’t think so. He did, after all, put forward the theory of natural selection as we now know it. Vestiges was a vast, mystical treatment of the origins of the universe (complete with some racial theorizing unsavory to contemporary eyes); Origin was a cautious work, anticipating every counterargument, bolstered with pages of evidence about pigeon breeding. Darwin made evolution a subject of scientific study.

He’s also a profoundly appealing figure. Unlike, say, Newton (combative, paranoid, devoted to his alchemy), Darwin the man was genuinely likeable. He had something of the attitude of the humble, persistent noodler. He measured armadillo fossils in the Galapagos, and thought it was odd that they resembled (but were not identical to) the armadillos his expedition was roasting for dinner over the campfire. He was a rigorous observer, but he also had a useful aimless curiosity. He was an abolitionist and a loving husband and father. We can sympathize with the loss of his daughter and his doubts about the theory of evolution. If we want to put a human face on science, we could do worse than Darwin.


Facebook, evolution, and mathematical modeling

In Biology, Delights, Math on February 12, 2009 at 6:09 pm

Slate has a neat article about Facebook’s new “25 things about me” craze. (For those who have remained blissfully ignorant: thousands of users wrote notes about random personal habits or goals, and tagged their friends in an expanding web of navel-gazing.) Turns out it can be modeled like an epidemic. A user is “contagious” for about one day — the day he tags a bunch of his friends in the note. After being tagged, most users respond within one day. Then response frequency drops off exponentially.

Here’s a nice Nature Review about the mathematics of modeling infectious disease.

biological infectiousness of influenza, HIV, and malaria

biological infectiousness of influenza, HIV, and malaria

The number of individuals that an infected person infects is given by a probability distribution. The probability that an infected person will infect another person within a small interval is

b(t) s dt

b is infectiousness, dt is an arbitrarily small amount of time, and s is the probability that the other person is infected.
If a group of individuals all have the same infectiousness, then the number of secondary infections that are caused by each infectious individual is a random number drawn from the Poisson distribution with mean R, where R is the expected number of new infected victims.

The interesting thing here is that the whole field of mathematical modeling of disease transmission isn’t going to be just a biological subject forever. It’s also going to be a behavioral subject. The idea that cultural ideas propagate and evolve like organisms isn’t new — it’s as old as Dawkins and his notion of “memes.” But back in the sixties he couldn’t have predicted just how concrete the similarities would be — that we could see the exact same differential equations governing Facebook crazes as malaria outbreaks. Watch as epidemiologists get drafted as marketing consultants in the next few years.