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Human Family Size
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University of Edinburgh Lecture notes for Reproductive Biology 3 Lecture "Human Family Size"
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Human Family Size, and Biology and Ethics of Assisted Reproduction At least 5 million babies have been born by IVF since 1978 (by 2012)
o At least one third of these were in the previous six years
o Around same time, it was reported that three babies are aborted every day
because of Down’s syndrome
o These stories are linked because the age of mothers is increasing due to IVF
and the risk of Down’s syndrome increases with maternal age
Chance of aneuploidy in general (abnormal number of chromosomes)
increases with maternal age
In 2014, more than half of babies were born to women over 30 for the first time ever
o Believed to be due to women contributing more to the workforce
o Couples are more likely to be biologically challenged if they leave having
children until later
Cyprus has the lowest total fertility rate in Western Europe
o All countries in Europe have rate below 2
Means that average number of children in a family is less than 2
o Europe is in need of more children being born
o Some countries are offering incentives for families to expand
Things such as free nursery care for parents who are trying to have more
children
In hunter-gatherer societies, families used to be fairly small with only 4-6 children
o Difficult to study family sizes in these societies but we can take cues from
tribes still living in remote deserts
o There was an increase in family size in the 18th and 19th century
Could see families with more than eight children
This is uncommon in today’s society
o In modern society, family size has once again decreased due mainly to
contraceptives and societal shifts
Most children born to one mother is 69
o Most children born to one father is believed to be around 1400
Over the years, there has been a shift around breast-feeding
o A signal is sent from the breast to the pituitary
o This signal causes oxytocin to be released which then causes milk let-down
o At the same time, prolactin is released which causes the production of more
milk
o Lactational Amenorrhea
When a baby is feeding the HPA axis feedback is disrupted
The pulsatile release of GnRH is disrupted which leads to decreased LH
This stops eggs being released from the ovary which means that the
baby is preventing competition from other offspring
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