Did Environmental Change Cause Human Evolution?

human-evolutionAfter reading this scholarly research on human evolution, I came to believe the authors’ hypothesis: Environmental change caused human change. See if you agree:

Evolution on a Restless Planet: Were Environmental Variability and Environmental Change Major Drivers of Human Evolution?
Peter J. Richerson, Robert L. Bettinger, and Robert Boyd
Two kinds of factors set the tempo and direction of organic and cultural evolution, those external to biotic evolutionary process, such as changes in the earth’s physical and chemical environments, and those internal to it, such as the time required for chance factors to lead lineages across adaptive valleys to a new niche space (Valentine 1985). The relative importance of these two sorts of processes is widely debated. Valentine (1973) argued that marine invertebrate diversity patterns responded to seafloor spreading as this process generated more or less niche space.

He suggested that natural selection is a powerful force and that earth’s biota are in near equilibrium with the niches available on the geological time scale. Walker and Valentine (1984) modeled the evolution of species assuming a logistic speciation rate limited by internal factors and a diversity-independent death rate caused by ongoing environmental change. Fitting this model to the observed evolution of shelled marine fossil-hominid-skullsinvertebrates suggests that the lag between extinctions and the evolution of new species leaves perhaps 30% of ecological niches unfilled. In this model, the biota lag environmental change by perhaps a few million years. However, as Valentine (1985) notes, if adaptive landscapes have whole suites of niches protected by deep maladaptive valleys, the waiting time for some pioneering species to cross the divide may be very long, generating the rare events that set new body plans and generate major adaptive radiations.

Eldredge and Gould (1972) and Gould (2002) championed the idea that internal processes such as genetic and developmental constraints, coupled with the complexity of the adaptive landscape, resulted in a highly historically contingent evolutionary process. On Gould’s account, most of the history of life had to do not with a relatively close tracking of a changing environment but with the halting evolutionary exploration a deeply fissured niche space, mostly by rapid bursts of evolution as a fissure was crossed, followed by long periods of stasis. Note that if the adaptive landscape is deeply fissured for any reason, evolution may take on a progressive character (Stewart 1997).

Imagine that the original simple forms of life began at the foot of a large mountain range of Handbook of Evolution, Vol. 2: The Evolution of Living Systems (Including Hominids) Edited by Franz M. Wuketits and Francisco J. Ayala Copyright © 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim ISBN: 3-527-30838-5 1268vch07.pmd 223 28.02.2005, 08:49 224 7 Evolution on a Restless Planet adaptive topography. Potentially, the whole history of life has been a halting and episodic process of moving first onto to local optima of the near foothills and subsequently filtering across adaptive chasms to higher peaks deeper into the complex topography. Perhaps we have not yet come anywhere near to reaching the highest peaks in the topography on earth, even after perhaps 3.5 billion years of life on our planet.

More complex scenarios are possible. Vermeij (1987) argues that much evolution is driven by the top-down biotic process of predator–prey coevolution, but that the degree of escalation of predator attack strategies and prey defenses is limited by external factors, especially those that control productivity. Vermeij does not commit himself on the issue of how closely the predator–prey escalation process tracks external environmental change. Discussions of the large-scale patterns of evolution typically assume that the overall environmental framework of the earth is static and that changes in features like the size of brains represent a series of progressive changes from simpler to more complex organisms. Billions of years have transpired since the origins of life on earth, and about 540 million years have transpired between the abundant fossil animals of the Cambrian and the evolution of humans.

If the earth’s environment has been essentially constant since either the origin of life or even the beginning of the Cambrian, the growth of organic complexity by natural selection and other evolutionary processes such as species selections would have to have been so limited by internal processes as to be exceedingly slow. On the other hand, since the discovery of seafloor spreading 40 years ago, the role of external factors in macroevolutionary processes has become much clearer (Valentine 1973). Today we have a reasonably clear picture of past continental configurations and past biogeochemistry, especially the chemistry of the oceans and atmosphere (Holland 1984; Scotese 2003). Past environments were very different from those of today.

For example, during the late Paleozoic, high oxygen concentrations in the atmosphere supported gigantic flying forms, including dragonflies a meter long and pterosaurs weighing perhaps 100 kg. (Graham et al. 1995; Dudley 2000). Everyone accepts, we suppose, that external processes are important regulators of the rate and direction of evolution in the very long run, and everyone accepts that evolution is not an instantaneous process. At the most extreme, life on earth could not begin to evolve until the earth formed, and new species do not evolve in one generation. But the gap is very wide between those that argue that most of the history of life, at least since the late Precambrian, is mainly regulated by internal processes and those that think that, for the most part, the earth’s biota are in near equilibrium with existing environmental conditions, aside from a few empty niches resulting from relatively short-term constraints operating on evolutionary processes. (more)



10 Responses to “Did Environmental Change Cause Human Evolution?”

  1. 1 bikram
    November 24, 2009 at 12:26 pm


    • November 24, 2009 at 9:08 pm

      Hi Bikram–What are your thoughts on this?

  2. 3 Chris Vise(Vice pres. Vise lol)
    January 20, 2010 at 4:23 am

    well for one, i am a christian….and i always thought you knew that climate change changed us…i dont believe its Evolution…i just symply believe its adaptation to the climate…even if evolution is true….it would of needed a mirical to start it…look up Dr william craig on youtube…hes amazing

    • January 20, 2010 at 5:44 am

      As a Christian, I too believe in miracles. As far as evolution or adaptation–you say potatoe, I say potato. Sounds like we agree.

  3. 5 James Thorton
    March 20, 2010 at 11:25 pm

    Well ofcource the environment causes evolition…the simple fact that people still question that shows how unclear people are with the topic of evolution. to address the christians above, “…i dont believe its Evolution…i just symply believe its adaptation to the climate”…that is evolution! ONE ORGANISM ADAPTING OVER TIME TO BETTER SUIT ITS ENVIRONMENT! that is evolution. Im not sure why everyone agrees that animals change and adapt to their environment over time yet so many deny it when its refered to as evolution.

    • 6 Chris Vise
      March 26, 2010 at 1:55 am

      Well my thought on adaptation is a little diff. then what most of you think. What I mean is that we prob. did change a little over time…but were still the same people! I do not think I was a rodent at one point. The adaptation what you all are talking about is simply another name for Evolution…so God Bless and take care

  4. 7 Spencer
    April 26, 2010 at 10:08 am

    What species do the skulls correspond to?

  5. April 26, 2010 at 11:06 pm

    Upper left corner to lower right:
    (A) Pan troglodytes, chimpanzee, modern
    (B) Australopithecus africanus, STS 5, 2.6 My
    (C) Australopithecus africanus, STS 71, 2.5 My
    (D) Homo habilis, KNM-ER 1813, 1.9 My
    (E) Homo habilis, OH24, 1.8 My
    (F) Homo rudolfensis, KNM-ER 1470, 1.8 My
    (G) Homo erectus, Dmanisi cranium D2700, 1.75 My
    (H) Homo ergaster (early H. erectus), KNM-ER 3733, 1.75 My
    (I) Homo heidelbergensis, “Rhodesia man,” 300,000 – 125,000 y
    (J) Homo sapiens neanderthalensis, La Ferrassie 1, 70,000 y
    (K) Homo sapiens neanderthalensis, La Chappelle-aux-Saints, 60,000 y
    (L) Homo sapiens neanderthalensis, Le Moustier, 45,000 y
    (M) Homo sapiens sapiens, Cro-Magnon I, 30,000 y
    (N) Homo sapiens sapiens, modern

    Mostly, the skull and brain get bigger but J, K, L of course are the exception, where Neanderthals had huge brains–as large as Homo sapiens sapines, to drive their unusually strong bodies.

    You can’t tell in this drawing, but H’s cousin (Homo erectus) had one of the thickest skulls of all humans. Makes you wonder what the matrix for survival was during their time.

    Thanks for dropping by.

  6. April 27, 2011 at 5:15 am

    The driving force of evolution are selective pressures, and climate change can be one such pressure. It has been well documented that species in the wild and in the laboratory evolve when subjected to selective pressures. By evolve I mean that the frequency of the expression of certain genes in the population changes. This process also applies to humans. But I don’t see climate change as a single thing. If the place where you are dries up you may move North say to a colder climate but you have to deal with surviving the trip, finding new sources of food and clothing, defending yourself against new predators, reworking the existing social order etc. It is a package deal with many selective pressures that are added on to the original one.

    • April 27, 2011 at 5:40 am

      Interesting, and of course true. Climate is just one force, albeit a every-changing one. This is probably one reason why most species last around 2 million years and no more. The world climate changes, as does everything else about earth. Thanks for your thoughts, Phantomimic.

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