r vs K

Humans have a tough time understanding evolution. I wonder if part of the problem actually stems from our biology.

The reproduction approach taken by most vertebrate animals fall somewhere between what are called r and K strategies. (See here for r/K theory and here for the subsequent improvement of it into life history theory.) To make a long story short, r strategies involve large numbers of offspring with the expectation that most will die off. K strategies involve fewer, higher quality offspring, that require more care but the investment pays off in higher quality reproduction.

It is no surprise that humans are consummate K strategists.

Of course, this is an oversimplification. There are lot of trade offs involving roles of organisms beyond individual reproduction, modification of environment, timing of events, etc. But the nice thing about the r/K metaphor is it captures the gamut of reproductive approaches.

Humans are mammals. Mammals are inherently in the K strategist arena– after all, no animal would evolve lactation that wasn’t. Birds are also K strategists with some interesting species that manage to get out of doing the job themselves, i.e., cuckoos. Consequently, we have a K-centric point of view.

The rest of the world is essentially based on r-strategy.

Mammals and birds together have about 16k species between them. The remaining 45k species of vertebrates (reptiles, amphibians and fish) are largely r-strategists, though some reptiles (e.g., crocodiles) and some fish (e.g., sticklebacks) do some post-egg care. Once the animals are hatched they’re essentially on their own.

But the non-vertebrates invertebrates comprise about 1.2 million species. Plants, fungie, etc., bring up the total to about 1.5 million species. Essentially all of them are r-strategists. That is, they put out a large number of potential new organisms that must fend for themselves. That doesn’t even include the microbes.

We are one little corner of a group (great apes) of a lesser order (primates) of a comparatively small class (mammals) that is clearly the minority (vertebrates.) We are a minority within a minority within a minority that does not follow the path laid down by older and wiser phyla.

Now, I would expect an intelligent organism to be self-involved and to consider it’s own heritage the best and most magnificent example of craftsmanship. But, had we evolved from, say, insects, we would be able to see the common ground between us and a million brethren. (God has an “inordinate fondness for beetles,” from J. B. S. Haldane.)

Or, we could have evolved from cephalopods. There would have been only 800 of our immediate brethren but we still would have shared our heritage with as many as 120k clams, oysters and snails.

Instead, we divide the world into vertebrate species and invertebrate species, dividing mammals (and ourselves) in one quick slice of taxonomy.

How many co-species do we have? Four: chimps, bonobos, orangutans and gorillas. All of them out of sight, out of mind, so we can safely forget them. We can see our resemblance in the 350 species of primates but the damage was done: our uniqueness trumps incidental resemblances to lesser species.

Is it a surprise we have trouble viewing ourselves as anything but uniquely gifted?




r vs K — 1 Comment

  1. But even within our species — even within this nation, for pete’s sake — there are people who are more K and others who lean r. Poll the students at an Ivy, or a top magnet school, and there’s a lot of onlies — brainy singletons who are the sole beneficiary of the assets of two parents and four grandparents. On the other hand there are plenty of American families who are running 4 or more kids; unless they are very well off the expectation there is that kids will be funding their own college tuitions.