Wait. What? Herbert Spencer was a Lamarckian?

While reading Peter J. Bowler’s The Eclipse of Darwinism, I was surprised to find out that the “social Darwinist”* Herbert Spencer was actually more Lamarckian than Darwinian. He apparently expressed Lamarckian views prior to the 1859 publication of The Origin of Species, and while he accepted Darwinian explanations and the theory of natural selection, Spencer believed Lamarckism – defined (here) as the inheritance of acquired characteristics through use/disuse – was the more important of the two theories. In fact, in his article, “The Inadequacy of Natural Selection,” Spencer states quite strongly that “either there has been inheritance of acquired characters, or there has been no evolution” (621).

Why did this “social Darwinist” think natural selection was inadequate? I think it can be boiled down to his belief that Darwinism couldn’t explain non-adaptive features and features that varied so finely that selection couldn’t detect them, as evidenced by his example of “skin discriminativeness,” or what we would now call tactical acuity.

Figure 1.

It is trivially true that your fingertips are more sensitive than the skin anywhere else on your body. In a series of experiments, Weber took a compass (the geometrical kind) and tested at what minimum distance a subject could detect the compass’s two points. For example, subjects could detect the two points 1/12 inch apart on their forefinger, but the points had to be 2.5 inches apart to be detected separately on the subject’s back. The rest of the body parts fell somewhere between 1/12 inches and 2.5 inches. (My MSPaint Figure 1 shows the “skin discriminativeness” Weber found among body parts.)

Why this distribution of tactical acuity? Why doesn’t all skin show the same acuity? According to Spencer, if this distribution is to be explained by natural selection, then there must be some kind of fitness benefit to having more sensitive fingertips and having one’s “thigh near the knee be twice as perceptive as the middle of the thigh” (604), but he is unable to offer one. Furthermore, he argues, would people with a more sensitive “thigh near the knee” survive and reproduce more than those who don’t? He thinks it unlikely – selection can’t see differences so miniscule.

Spencer notes that blind people, especially those who read Braille, as well as typesetters, show higher tactile acuity than normal. He claims this is “clear proof” that skin discriminativeness is an acquired trait (605) and suggests that when the skin touches objects, additional nerve growth is stimulated which increases tactile acuity (647). This explains why the back has the least sensitive skin – it just touches clothes – whereas the stomach has slightly more as it is explored by the hands more frequently. The nose is more sensitive than the forehead because we rub our nose more, and our palms are less sensitive than our fingertips because the fingertips manipulate while the palms merely help grasp. The more used a body part is, the higher tactile acuity it shows.

Spencer thinks his argument is solidified when he brings up the tip of the tongue. Weber found that the tongue tip has double the sensitivity of the fingertips, but Spencer doesn’t think the increased sensitivity is because of some selective advantage. He argues that food is moved by the body of the tongue, not the tip, and while the tip is used in making some sounds, people can get by with less sensitive tongues. Instead, much like skin sensitivity, Spencer believes the tongue tip’s acuity is a result of constant environmental stimulation – the tongue is continually exploring the mouth and teeth. There is no adaptive function for having a tongue that can sense two points 1/24 inches apart, according to Spencer.

So now we have a standard Lamarckian explanation of tactile acuity: the more use, the more nerve growth, the more acute.** His argument is also non-adaptive and very much not (ultra)Darwinian.

Spencer’s argument was challenged by at least three people: the neo-Darwinians Alfred Russell Wallace and August Weismann as well as psychologist James McKeen Cattell. The dispute with Wallace is rather uninteresting: Wallace claims skin sensitiveness is a result of natural selection and Spencer disagrees but both claim the facts are on their side (646). Weismann points out that the other apes use the tongue as “an organ of touch,” but Spencer still disputes that selection could detect such fine-scale differences (like between 1/24 inches and 1/20 inches). Spencer further points out that Weismann’s argument is “suicidal” because it refutes Weismann’s own theory of panmixia – that traits may be lost because selection on the trait is removed – which has apparently not taken place in the human tongue as it is still extremely sensitive (665). Cattell points out that “relatively great accuracy of discrimination can be quickly acquired by ‘increased interest and attention. … Practice for a few minutes will double the accuracy of discrimination, and practice on one side of the body is carried over to the other’” (666). Spencer dismisses this challenge, claiming that those studies actually showed that the subjects were only able “to learn to discriminate between the massiveness of a sensation produced by two points and the massiveness of that produced by one, and to infer one point or two points accordingly” (666). While Spencer’s pro-Lamarckian arguments seem weak, being based on crude experiments and hearsay, he was able to handily refute his opponents as well.

However, the most problematic part of Spencer’s argument in my mind is the issue of heredity. For some reason, Wallace and Weismann never address the issue. James McKeen Cattell does challenge Spencer on this point, but Spencer leaves this problem unanswered. Was proving heredity not as essential in this period as it is today? Spencer apparently felt he showed that acquired traits were inheritable in Factors of Organic Evolution (which I have yet to read), but he didn’t even attempt to show that increased tactile acuity was.

So yes, Spencer was indeed a Lamarckian. In addition to skin discriminativeness, he thought the reduced size of the little toe in humans, the evolution of jumping, and the antlers of the Irish elk were Lamarckian features. Perhaps I should have known this already, but it seems strange that a man known for “social Darwinism” was actually a Lamarckian. He did accept Darwinian explanations for some features, but he thought natural selection was well, inadequate. He believed that Darwinism couldn’t explain non-adaptive traits, traits that varied in minuscule gradations, and traits that required parallel variations in other traits. Lamarckism filled those gaps in Spencer’s eyes.

* Eric Michael Johnson has a great series of posts on why “social Darwinism” is such a problematic term and also discusses some of Herbert Spencer’s beliefs, called “Deconstructing Social Darwinism.”

** A question I am interested in is: Was Spencer right or wrong on this point?  According to this study, “Tactile Spatial Acuity Enhancement in Blindness: Evidence for Experience-Dependent Mechanisms,” blind people do outperform the non-blind in tactile acuity and that touch is “the trigger for tactile spatial acuity enhancement.” They say the results suggest “the action of underlying experience-dependent neural mechanisms such as somatosensory and/or cross-modal cortical plasticity” but I have no idea what that means. Is this nerve growth or something else?

________________________

Spencer, Herbert. “Appendix B. The Inadequacy of Natural Selection, Etc., Etc.” The Principles of Biology. Revised and Enlarged Edition. Vol. 1. New York: D. Appleton and, 1898. 602-91. Print.

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