vol.1,no.1,1-30,l. van valen, a new evolutionary law

7/21/2019 Vol.1,No.1,1-30,L. Van Valen, A New Evolutionary Law.

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A NEW EVOLI.NIONANY LAWLeigh Van ValenDepartment of BiologyThe University of ChicagoChicago, I l l inois 60537

ASSTRACT:A11 groups for which data exist go extinct at a rate that is constant fora given group. When this is recast in ecological for:n (the effectiveenvironment of any homogeneous group of organisms d.eteriorates at a stochasti-ca11y constant rate), no tlefinite exceptions exist although a fev are possible.Extinction "ates are similar within some very broad categories ancl varyregularly with size of area inhablted.. A new unit of rates for discretephenomena, the macarthur, is introduced.. Laws are appropriate in evolutionarybiology. Truth needs more than correet pred.ictions. The Law of Extinctionis evidence for eeological slgnifieance and. eomparability of taxa. A ncn-Markovian hypothesis to explain the law invokes mutually incompatible optimavithin an ad.aptive zone. A self*perpetuating fluctuation results vhich ca nbe stated. in terms of an unstudied aspect of zero-sun gnrns theory. fhehypothesis can be derived from a view that momentary fitness is the e,mountof control of resources, whieh rernain eonstant in total- anount. The hypothesisinplies that long-term fitness has only two eomponents and. that eventg ofmutualism are rare. The hypothesis largely explains the observed pattern ofmolecu]-ar evolution.

IntroductionDuring a study (Van Valen, submitted.) on the effects of extinction Ivanted to show that a modeL l was using was oversimplified.. It assumed no

correlation of probability of extinction with age of the group, antl f thoughtthat general1y more vulnerable groups should d.ie out first. A test using datafrom Simpson (1953) showed. o my astonishment that the assumption wasreasonably correct in these cases. I d"id. not believe it could be generallytrue and so tested these and other cases in more detail-. The assr:nptionproved to be consistent with all available data. Others (unpublished results)have now confir:ned this fincting for ind.ividual taxa. I will present a moreextend.ed" reatment efsewhere; the present paper is contlensed..The Evidence

Ttre method is an application of the survivorship curve of populationecology (includ.ing d.emography). It is a simple plot of the proportion of theoriginal sanple that survive for various interval-s. In this case the sa,mpleis the set of all known subgroups of some larger group, no matter when inabsolute time each subgroup originatecl. A logarithmic ord.inate, stand.ard.in eeology, gives the property that the slope of the curve at any age isproportional to the probability of extinction at that age. Simpson (f9\\,1953) compiled two well-knovn taxonomic survivorship curves but used anar it tmetic ordinate (f- )+) .The results (fig;.-1-5) for over 25'OOO subtaxa show aL:nost unifotrnlinearity for extinct taxa except for effects attributabl-e to sa,npling error(216). Sa.mpl-ingerror is most noticeabl-e at the bottom of the graphs, whereEvol . Theory 1:1-30 ( . lu lY 1973)


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vol.1,no.1,1-30,l. van valen, a new evolutionary law

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