Concepts explained
Lamarck — Wrong for More Complicated Reasons Than You Think
The man who said giraffes stretched their necks. School usually stops there and moves on to the ridicule. But his first claim was not that one, and the claim he is blamed for was not his alone. Nor is it true, as is often said now, that epigenetics has vindicated him. This article has to be careful in both directions.
Unlike the previous four, this article has to be careful in two directions. The ridicule is not accurate — and neither is the claim that he turned out to be right.
What he said first
Start with what the world of 1809 was like.
Linnaean taxonomy ruled. Species were fixed as created, and to classify them was to copy out the design of God. To say that species change was not scholarship but impiety.
Into that Lamarck published Philosophie zoologique. The first line of his claim is not about giraffes. It is that living things change over time — fifty years before Darwin.
Two laws, and a label wrongly attached
His account has two parts.
- Organs used a great deal develop; organs unused waste away — use and disuse.
- Changes acquired in a lifetime pass to the offspring — the inheritance of acquired characteristics.
What was distinctively his lies rather in the character of the first law: living things have an inner tendency towards complexity, and when conditions change an animal strives to meet them.
Nine hundred mouse tails
In the 1880s August Weismann ran a very simple experiment: he cut off the tails of mice and bred them, then cut the tails of their offspring and bred again.
Five generations, more than nine hundred mice. Not one was born with a shortened tail.
Once Mendel was rediscovered and Morgan had placed genes on chromosomes, the picture was plain: inheritance travels in particles, and there is no route by which events in the body are written into them.
With the of the 1930s, Lamarckian inheritance was formally out of evolutionary theory.
A little further in
So why has the name come back?
One reads it constantly: epigenetics has shown that Lamarck was right after all.
It is not so — though it is easy to see how the idea arises. Start with what epigenetics actually is.
And there are real observations. Experiences such as famine or severe stress alter these marks, and some of the marks are found again in the next generation. In plants the effect is quite clear; in mammals there are cases.
Put that way it sounds like Lamarck. It is not, for four reasons.
- There is no direction. Lamarck's point was that using a thing develops it and the development is passed on. Epigenetic marks do not supply an advantageous trait to order. The traces of famine show up less as a body hardened against famine than as a body with disordered metabolism. The blacksmith's son is still not born with thick arms.
- They are mostly erased. In mammals the marks are wiped on a large scale twice — just after fertilisation and again when germ cells are formed. What survives is exceptional and usually gone within a few generations.
- The sequence does not change. Evolution is a lasting change in a population's genetic make-up, and a mark erased within a few generations cannot supply the raw material for that.
- The machinery is itself genetic. The enzymes that attach and remove the marks are written in DNA. The whole epigenetic system is a product of natural selection.
Why the story travels so well
A figure taught as wrong turning out to have been right is always attractive. Sympathy runs to the suppressed, and a reversal of the textbook is memorable.
And such cases do exist. The last article in this series is exactly one — a man who was right and was refused.
Lysenko, as a warning
There is an example of why none of this is a trifle.
In the 1930s Trofim Lysenko made acquired inheritance into state science in the Soviet Union, because a picture in which effort changes a nature and the change is handed on suited the ideology of the day. To speak of genes was to be a reactionary.
What he left
in a world where species were fixed as created, he was the first to say publicly that they alter over time
he coined the word and laid the groundwork for invertebrate taxonomy
the same genes do grow differently in different conditions. What is acquired that way simply does not pass on
- 1735Linnaeus — a system in which species are fixed as created
- 1809Lamarck — Philosophie zoologique says species change
- 1859Darwin — undirected variation and selection
- 1865Mendel — inheritance comes in particles
- 1889Weismann — the mouse-tail experiment and germ-plasm theory
- 1937The modern synthesis — Lamarckian inheritance formally excluded
- 1940sLysenko — acquired inheritance becomes state science in the USSR
- 1942Waddington — coins 'epigenetics', to explain development
- 1953Watson and Crick — the structure of DNA
- 2000sReports of epigenetic marks crossing generations begin
The question that remainsLamarck was unfairly mocked and fairly wrong. Both sentences are true together. When we file someone away as the one who was wrong, how much of what they got right goes into the drawer with them?