The presence of a child's biological mother in the household increases expenditure on an important
input into the production of healthy children - food. That is startling conclusion of a new study by
Professor Anne Case, I-Fen Lin and Sara McLanahan, published in the latest issue of the
Economic Journal. They document evidence from both the United States and South Africa
showing that adoptive, step and foster mothers invest significantly less in their children than
comparable biological mothers do. This seems to be because they are less interested in sustaining
someone else's genetic line.
Using data from the United States for 6,000 households over the period 1968-85, the study
analyses how the level of food expenditure varies with different types of parental arrangements.
Household size, composition and characteristics vary with family structure. Hence the authors
control for a wide range of household characteristics that may determine food expenditure
(household income, household size, hours worked, age, race, education, etc.) so as to focus on the
singular effects that family structure has on child expenditure.
The results show that for each child living with their birth mother, food spending is 5% higher -
i.e. food expenditure would fall by 5% if a biological child was replaced by a non-biological child.
The researchers identify at least two possible explanations for this finding:
l Non-biological parents may invest less in non-biological children because they expect to
receive lower transfers of time and money from these children in later life. While nonbiological
children may be close to their non-biological parents, they may have multiple
sets of parents, thus reducing the anticipated per-parent return on a given investment. This
is the Economic Motive.
l Non-biological parents may not care about sustaining someone else's genetic line so they
will invest less in someone else's children. This is the Biological Motive.
The data identifies four main types of family structure and the researchers rank these in order of
attachment to the parent: biological; adopted; step; and foster. They argue that if the Economic
Motive is correct, then we would expect to see differences in the treatment of different types of
non-biological children - i.e. most money spent on biological, then adopted, then step and finally
foster children.
But if the Biological Motive is correct, then we would expect to see all non-biological children
(adopted, step and foster) treated the same and biological children treated better. And this is
exactly what the data show. Non-biological children experience significantly reduced food
spending, regardless of the type of non-biological tie that binds the mother to the child. The
genetic tie to the child, and not any anticipated future economic tie, appears to be the tie that
binds.
The data for South Africa are more detailed and the researchers are able to determine the types of
food on which different households spend their money. Using data from 1995 for over 18,000
households, they find that as in the United States, the presence of a biological mother raises food
expenditure. But what is more, if the biological mother is not present in the household, then less is
spent on healthy foods - milk, fruit and vegetables - and children's clothes and more is spent on
alcohol and tobacco.
Note for Editors: 'How Hungry is the Selfish Gene?' by Anne Case, I-Fen Lin and Sara
McLanahan is published in the October 2000 issue of the Economic Journal. The authors are at
Princeton University.
For Further Information: contact RES Media Consultant Romesh Vaitilingam on 0117-983-
9770 or 07768-661095 (email: romesh@compuserve.com); or RES Media Assistant Niall Flynn
on 020-7878-2919 (email: nflynn@cepr.org).