Survival of the traits

Mammals can pass along acquired characteristics to their offspring, according to a new study.


Arthur Allen
November 4, 1999 10:00PM (UTC)

If you remember your ninth-grade biology, you probably remember the Frenchman Jean-Baptiste Lamarck as one of the wacky also-rans of modern science. He was the predecessor of Darwin whose theory of acquired characteristics held that the stature of the giraffe came from generations of giraffe parents straining their necks ever farther to reach the leafy branches of the banyan tree, then -- and this was the wacky part -- passing their long necks on to their kids. For a century Lamarckism has been joke science, a notch below creationism, buried ever deeper under Darwin's theory of natural selection. But if a study published Monday in the influential journal Nature Genetics is any indication, Lamarck may be due for a rehabilitation, of sorts.

In the work published in Nature Genetics, Emma Whitelaw and her colleagues at the University of Sydney did a set of experiments with a particular strain of lab mice. The odd thing about this strain, which had been observed previously, was that despite being genetically identical, some of the mice were yellow, others gray-striped, others a mix of yellow and stripes. The researchers found that the differences were caused by subtle changes in the mice's DNA during their fetal development.

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Whitelaw's even more surprising observation was that all the mice whose mothers had yellow coats always had yellow coats as well. In other words, the non-genetic change that occurred in the female mouse fetus was somehow passed along to her offspring when she became a mother. Even when the mouse embryos were nurtured in the wombs of surrogate mothers, their coat color was the same as that of the "genetic" mother.

Whitelaw's work is apparently the first showing that mammals can somehow pass along acquired characteristics to the next generation. It isn't quite as remarkable as Lamarck's giraffes inheriting stretched necks, but it is, strictly speaking, proof of Lamarckian inheritance.

The study is part of a growing field called epigenetics, a branch of developmental biology that investigates the mechanisms whereby certain genes are suppressed through changes in the chemical makeup and shape of the DNA in which they are embedded.

We all know how genes are supposed to work in the classic Mendelian scheme of inheritance: You get a copy or two of the fat gene, depending on whether or not it's recessive or dominant, and that makes you fat. Complicating matters, many conditions don't fit into a neat Mendelian box. It's known that schizophrenia is largely inherited, for example, but after years of unsuccessfully trying to locate single genes for schizophrenia, scientists believe that many different genes operating in different combinations contribute to the ailment.

Epigenetics adds yet a further complication to the picture. Instead of just a lot of genes operating together, it turns out, subtle, random changes in the chemistry of the DNA itself affect which of those genes actually fire into action.

Just how prominently epigenetics figures in the overall scheme of things -- how big a role they play, for example, in human traits and disease -- isn't yet known. But epigenetics studies have multiplied in the past decade and there is already clear evidence of epigenetic effects.

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For example, many genes function only in men or women because of a gene-suppressing action called imprinting. Prader-Willi syndrome, a rare genetic disease, and Angelman syndrome, a neurological disorder, are both the result of subtle changes in the expression of a gene on chromosome 15. Prader-Willi manifests itself only when the DNA mutation is inherited from a father; Angelman syndrome from the mother.

In the nature vs. nurture debate, epigenetics falls under the category "the nurture of nature." As billions of dollars are poured into the Human Genome Project, it's worth pointing out, as does Eva Jablonka of Tel Aviv University, that "DNA sequence information is not sufficient for understanding the intricacies of biological inheritance." It's not that genetic effects aren't important, or the genome project any less valuable than its hype. Rather, scientists working on the fringe of genetics are pointing to some of the other factors that impinge on the success of genes.

So what does this have to do with Lamarck? It now appears -- Whitelaw's study is a good example -- that some of the alterations in gene function resulting from epigenetic changes can be passed along to the next generation. Ted Steele, another Australian scientist, made this argument strongly in a book he published earlier this year, "Lamarck's Signature: How Retrogenes are Changing Darwin's Natural Selection Paradigm."

Steele argues intriguingly that the coding for the production of antibodies to certain viral or bacterial attackers might be transcribed into the DNA of human somatic, or non-sexual cells, then somehow transferred from somatic to germ line cells -- sperm and ova. Steele presents a plausible case for such a transfer, but no direct evidence for it.

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However, Whitelaw's article does present evidence for such a transfer. The yellow-coat color apparently comes about by means of an epigenetic change caused when a particle called a retrotransposon -- a gene that moves around the genome -- settles during fetal development in DNA near the color gene. How the retrotransposon was passed along to germ line cells, and thus inherited, isn't clear.

The patterns Whitelaw observed "seem heretical in their Lamarckian character," write developmental biologists Rosalind John and Azim Surani in an article accompanying Whitelaw's paper, "but they do occur and are therefore worth serious consideration."

As it happens, this kind of gene change has been shown to be quite common in plants, and is probably also common -- though harder to observe -- in animals, says Robert A. Martienssen, a scientist at Cold Springs Harbor Laboratory who has an article about plant epigenetics in the same issue of Nature Genetics. "To the extent there is Lamarckian inheritance, it occurs through epigenetics," he says.

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Darwin, embarrassingly to the neo-Darwinians, was a great admirer of Lamarck (1744-1829) and incorporated his theories into work he published after "Origin of Species." The Stalinist agriculture czar T.D. Lysenko gave Lamarckism an enduringly bad name. Convinced that Lamarck was a better Marxist than Darwin, Lysenko gutted Soviet agricultural science and fruitlessly tried to improve grain harvests by experimenting with adult plants in the vain hope they would pass along the changes he made. Meanwhile, millions starved on collective farms.

But now that the Cold War is over, perhaps a neo-Lamarckian rebirth is overdue. Bring on the giraffes!


Arthur Allen

Arthur Allen writes on health, science and other issues for Salon. He lives in Washington.

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