This document summarizes key biological, brain, and health changes that occur throughout the human lifespan from infancy to death. It describes physical growth patterns in infancy and early childhood, rapid brain development in the first years, and common health issues such as SIDS. During middle childhood, it notes brain frontal lobe growth and increasing risks of obesity and accidents. Puberty and adolescent biological changes, brain maturation continuing into early adulthood, and potential health problems like eating disorders are reviewed. Changes in early, middle and late adulthood as well as the biological processes occurring at death are summarized.

1. BIRTH TO DEATH:
HUMAN LIFESPAN
DEVELOPMENT
GROUP 7
ALLIANT INTERNATIONAL UNIVERSITY

2. INFANCY (0-2
YEARS)
BIOLOGICAL CHANGES:
 AVERAGE AMERICAN NEWBORN SIZE IS
ABOUT 20 INCHES LONG AND 7.5
POUNDS
 DURING FIRST FEW DAYS, INFANTS
LOST 5-7% OF THEIR TOTAL WEIGHTS,
BUT HEIGHT AND WEIGHT INCREASED
RAPIDLY AFTER THAT. BY TWO YEARS
OLD, THE WEIGHT IS ABOUT 26-32
POUNDS AND HEIGHT IS 32-35 INCHES
 AT BIRTH, THE NEONATE'S BRAIN
WEIGHS ONLY 25% OF AN ADULT
BRAIN. BY THE END OF THE SECOND
YEAR, THE BRAIN WEIGHS ABOUT 80%
ALREADY.
 TWO IMPORTANT PATTERNS OF
GROWTH- CEPHALOCAUDAL PATTERN
AND PROXIMODISTAL PATTERN
This Photo by Unknown Author is licensed under CC BY-NC-ND

3. INFANCY
(CONT.)
BRAIN CHANGES:
 SENSATION AND PERCEPTION ARE
BEING DEVELOPED DURING
INFANCY.
 INFANTS ARE AWARE OF DEPTH,
SIZE AND SHAPE CONSTANCY.
 CLASSICAL CONDITIONING,
OBSERVATIONAL CONDITIONING,
AND OPERANT CONDITIONING
EXPLAIN EXPERIENCE OF INFANTS’
RESULTS IN RELATIVELY
PERMANENT CHANGE IN
BEHAVIOR
This Photo by Unknown Author is licensed under CC BY-NC-ND

4. INFANCY (CONT.)
HEALTH CHANGES:
 TWO IMPORTANT INFLUENCES TO CHILDREN HEALTH ARE PREVENTION AND POVERTY
 INFANTS NEED CLOSE MONITORING AS THEY GAIN LOCOMOTOR AND MANIPULATIVE SKILLS ALONG
WITH A STRONG CURIOSITY TO EXPLORE THEIR ENVIRONMENT. THE PREVENTION STARTS BY
PARENTS OR CAREGIVERS TO KEEP THEIR CHILDREN ON A TIMELY IMMUNIZATION SCHEDULE AND
AVOID ACCIDENTS THAT ARE THE LEADING CAUSE OF DEATH DURING THE INFANCY.
 PHENYLKETONURIA (PKU) IS AN INHERITED METABOLIC DISORDER IN WHICH A CHILD LACKS
PHENYLALANINE HYDROXYLASE, THE ENZYME NECESSARY TO ELIMINATE
EXCESS PHENYLALANINE, AN ESSENTIAL AMINO ACID, FROM THE BODY. FAILURE TO FEED A SPECIAL
DIET TO A CHILD WITH PKU IN THE FIRST 3 TO 6 WEEKS OF LIFE WILL RESULT IN MENTALLY
RETARDATION.
 BIRTH TRAUMA, LOW BIRTH WEIGHT, AND EARLY SICKNESS CAN AFFECT LATER PHYSICAL AND
MENTAL HEALTH BUT USUALLY ONLY IF THESE CHILDREN GROW UP IN IMPOVERISHED
ENVIRONMENTS. SUDDEN INFANT DEATH SYNDROME (SIDS) IS A CONDITION THAT OCCURS WHEN
INFANTS STOP BREATHING, USUALLY DURING THE NIGHT, AND DIE SUDDENLY WITHOUT AN
APPARENT CAUSE. SIDS REMAINS THE HIGHEST CAUSE OF INFANT DEATH IN THE UNITED STATES.
This Photo by Unknown Author is licensed under CC BY-ND

5. EARLY
CHILDHOOD
(2-6 YEARS)
BIOLOGICAL CHANGES:
 CHILDREN SLIM DOWN AS THEIR
BODY LENGTHEN. THEIR HEADS ARE
STILL LARGE FOR THEIR BODIES.
GIRLS ARE SLIGHTLY SMALLER AND
LIGHTER THAN BOYS DURING THESE
YEARS. BOYS TEND TO HAVE MORE
MUSCLE MASS THAN GIRLS AND
GIRLS HAVE MORE FATTY ISSUES
THAN BOYS.
 DURING THIS STAGE, EACH YEAR
CHILD GROWS AN ADDITIONAL 2-3
INCHES AND GAINS ABOUT 4-6
POUNDS. HOWEVER, THE FIGURES
ARE DIFFERENT FROM CHILD TO
CHILD. IT DEPENDS ON THEIR
GENETIC INFLUENCES, NUTRITION,
AND ETHNIC ORIGIN.
This Photo by Unknown Author is licensed under CC BY-SA

6. EARLY CHILDHOOD (CONT.)
BRAIN CHANGES:
 DURING EARLY CHILDHOOD, THE BRAIN AND HEAD GROW MORE
RAPIDLY THAN ANY OTHER PART OF THE BODY.
 THERE’S LATERALIZATION OF THE TWO HEMISPHERES OF THE BRAIN.
THE TWO CEREBRAL HEMISPHERES DEVELOP AT DIFFERENT RATES,
WITH THE LEFT HEMISPHERE DEVELOPING MORE FULLY IN EARLY
CHILDHOOD (AGES 2 TO 6), AND THE RIGHT HEMISPHERE
DEVELOPING MORE FULLY IN MIDDLE CHILDHOOD (AGES 7 TO 11).
THE LEFT HEMISPHERE PREDOMINATES EARLIER AND LONGER,
WHICH MAY EXPLAIN WHY CHILDREN ACQUIRE LANGUAGE SO EARLY
AND QUICKLY.
 ANOTHER ASPECT OF BRAIN DEVELOPMENT IS HANDEDNESS, OR
PREFERENCE FOR USING ONE HAND OVER THE OTHER.
This Photo by Unknown Author is licensed under CC BY-SA

7. EARLY CHILDHOOD (CONT.)
HEALTH CHANGES:
 PRESCHOOLERS' LUNGS HAVE NOT YET FULLY DEVELOPED, SO RESPIRATORY
AILMENTS ARE THE MOST COMMON ILLNESSES AMONG CHILDREN AT THIS
AGE
 MOST CHILDHOOD ILLNESSES USUALLY DO NOT REQUIRE A PHYSICIAN'S OR
NURSE'S ATTENTION. ADDITIONALLY, MINOR ILLNESSES MAY HELP CHILDREN
TO LEARN COPING SKILLS, SUCH AS DEAL WITH PHYSICAL DISCOMFORT AND
DISTRESS.
 POVERTY, FAMILY STRESS, BEING IN DAYCARE, OR BEING FROM A LARGE
FAMILY IS CORRELATED WITH INCREASED RISK OF ILLNESS IN THE
PRESCHOOLER AGE GROUP.
 MOST DEATHS DURING EARLY CHILDHOOD ARE DUE TO ACCIDENTAL INJURIES
RATHER THAN ILLNESSES. THE MOST COMMON SOURCE OF DEADLY
ACCIDENTS FOR PRESCHOOLERS IS THE AUTOMOBILE.
This Photo by Unknown Author is licensed under CC BY-SA

8. MIDDLE CHILDHOOD (7-11
YEARS)
BIOLOGICAL CHANGES:
 CHILDREN GROW SLOWLY AND CONSISTENTLY DURING THIS
STAGE BEFORE THE RAPID GROWTH OF ADOLESCENCE.
 CHILDREN GROW ABOUT 2-3 INCHES PER YEAR AND 7 POUNDS
PER YEAR UNTIL PUBERTY.
 SKELETAL BONES AND MUSCLES BROADEN AND LENGTHEN,
WHICH MAY CAUSE CHILDREN TO EXPERIENCE GROWING PAINS.
 SKELETAL GROWTH IN MIDDLE CHILDHOOD IS ALSO
ASSOCIATED WITH LOSING THE DECIDUOUS TEETH (BABY
TEETH).
 THROUGHOUT MOST OF MIDDLE CHILDHOOD, GIRLS ARE
SMALLER THAN BOYS AND HAVE LESS MUSCLE MASS.
This Photo by Unknown Author is licensed under CC BY-NC-ND

9. MIDDLE
CHILDHOOD
(CONT.)
BRAIN CHANGES:
 FRONTAL LOBES ARE GROWING AND
THEY ARE RESPONSIBLE FOR PLANNING,
REASONING, SOCIAL JUDGMENT, AND
ETHICAL DECISION MAKING, AMONG
OTHER FUNCTIONS. DAMAGE TO THIS
PART OF BRAIN RESULTS IN ERRATIC
EMOTIONAL OUTBURSTS, INABILITY TO
PLAN, AND POOR JUDGMENT.
 LATERALIZATION OF THE TWO
HEMISPHERES OF THE BRAIN, ALSO
CONTINUES DURING MIDDLE
CHILDHOOD
 CORPUS CALLOSUM AND OTHER AREAS
OF THE NERVOUS SYSTEM BECOME
MORE MATURE
This Photo by Unknown Author is licensed under CC BY-SA-NC

10. MIDDLE
CHILDHOOD
(CONT.)
HEALTH CHANGES:
 THE TYPICAL MINOR ILLNESSES OF EARLY CHILDHOOD—COLDS, COUGHS, AND STOMACHACHES—ARE LIKELY TO
LESSEN IN FREQUENCY IN MIDDLE CHILDHOOD.
 MINOR ILLNESSES MAY HELP CHILDREN LEARN PSYCHOLOGICAL COPING SKILLS AND STRATEGIES FOR DEALING
WITH PHYSICAL DISCOMFORTS.
 ABOUT 25% OF MIDDLE CHILDHOOD IN THE UNITED STATES TODAY ARE OBESE, AND MOST OF THESE CHILDREN GO
ON TO BECOME OBESE ADULTS. OBESITY IN ADULTHOOD IS RELATED TO HEART PROBLEMS, HIGH BLOOD
PRESSURE, AND DIABETES.
 IN THE UNITED STATES, NEARLY 22 MILLION CHILDREN ARE HURT IN ACCIDENTS EACH YEAR. FOR CHILDREN, THE
MOST COMMON DEADLY ACCIDENTS RESULT FROM BEING STRUCK BY MOVING VEHICLES

11. ADOLESCENCE (12-19 YEARS)
BIOLOGICAL CHANGES:
 THE START OF ADOLESCENCE ALSO MARKS THE BEGINNING OF FREUD'S FINAL STAGE OF PSYCHOSEXUAL
DEVELOPMENT, THE GENITAL STAGE
 THE SPEED AT WHICH ADOLESCENTS SEXUALLY MATURE VARIES; THE BEGINNING OF PUBERTY IN BOTH
GENDERS FALLS WITHIN A RANGE OF 6 TO 7 YEARS.
 MALE PUBERTAL CHARACTERISTICS TYPICALLY DEVELOP IN THIS ORDER: INCREASE IN PENIS AND TESTICLE
SIZE, APPEARANCE OF STRAIGHT PUBIC HAIR, MINOR VOICE CHANGE, FIRST EJACULATION, APPEARANCE
OF CURLY PUBIC HAIR, ONSET OF MAXIMUM GROWTH IN HEIGHT AND WEIGHT, GROWTH OF HAIR IN
ARMPITS, MORE DETECTABLE VOICE CHANGES, AND, FINALLY, GROWTH OF FACIAL HAIR.
 FEMALE PUBERTAL CHARACTERISTICS DEVELOP IN THIS ORDER: THEIR BREASTS ENLARGE, OR PUBIC HAIR
APPEARS. LATER, HAIR APPEARS IN THE ARMPITS. AS THESE CHANGES OCCUR, THE FEMALE GROWS IN
HEIGHT AND HER HIPS BECOME WIDER THAN HER SHOULDERS. AND GIRLS HAVE THEIR FIRST
MENSTRUATION-MENARCHE.
 THE ENDOCRINE SYSTEM’S ROLE IN PUBERTY INVOLVES THE INTERACTION OF THE HYPOTHALAMUS, THE
PITUITARY GLAND, AND THE GONADS.
 THE CONCENTRATIONS OF TWO KEY HORMONES INCREASE IN PUBERTY, AND THE CHANGES ARE VERY
DIFFERENT IN BOYS AND GIRLS: TESTOSTERONE IS A HORMONE ASSOCIATED IN BOYS WITH THE
DEVELOPMENT OF GENITALS, INCREASED HEIGHT, AND DEEPENING OF THE VOICE. ESTRADIOL IS A TYPE
OF ESTROGEN ASSOCIATED IN GIRLS WITH BREAST, UTERINE, AND SKELETAL DEVELOPMENT.
This Photo by Unknown Author is licensed under CC BY-SA-NC

12. ADOLESCENCE
(CONT.)BRAIN CHANGES:
 SCIENTISTS HAVE DISCOVERED THAT ADOLESCENTS’
BRAINS UNDERGO SIGNIFICANT STRUCTURAL CHANGES
 THESE STRUCTURAL CHANGES OCCUR IN THE CORPUS
CALLOSUM, THE PREFRONTAL CORTEX, AND THE LIMBIC
SYSTEM. THE CORPUS CALLOSUM THICKENS IN
ADOLESCENCE, WHICH IMPROVES ADOLESCENTS’
ABILITY TO PROCESS INFORMATION. THE PREFRONTAL
CORTEX DOESN’T FINISH MATURING UNTIL THE
EMERGING ADULT YEARS. THE LIMBIC SYSTEM, WHICH IS
THE SEAT OF EMOTIONS AND WHERE REWARDS ARE
EXPERIENCED, MATURES MUCH EARLIER THAN THE
PREFRONTAL CORTEX AND IS ALMOST COMPLETELY
DEVELOPED BY EARLY ADOLESCENCE. AMYGDALA IN THE
LIMBIC SYSTEM INVOLVES ON EMOTION, AND IT LEADS
TO CERTAIN BEHAVIOR IN ADOLESCENCE.
 OXYTOCIN & DOPAMINE ARE TWO MAJOR HORMONES
INCREASE A LOT INSIDE THE ADOLESCENT'S BRAIN.
INCREASING BONDING IS ONE OF OXYTOCIN MAIN
FUNCTIONS. WHEN DOPAMINE IS PRODUCED, IT GIVES
HUMAN A STRONG SENSE OF SATISFACTION.
 INCREASES IN DOPAMINE HORMONE HAVE BEEN LINKED
TO INCREASED RISK TAKING AND THE USE OF ADDICTIVE
DRUGS

13. ADOLESCENCE
(CONT.)HEALTH CHANGES:
 THREE POSSIBLE MAJOR HEALTH PROBLEMS INCLUDE
EATING DISORDERS, DEPRESSION, AND SUBSTANCE
ABUSE. THE MOST COMMON OF THESE AMONG
TEENAGERS IS OBESITY
 OBESITY CARRIES WITH IT THE POTENTIAL FOR SOCIAL
STIGMA, PSYCHOLOGICAL DISTRESS, AND CHRONIC
HEALTH PROBLEMS.
 ANOREXIA NERVOSA, OR SELF‐STARVATION. THE
TYPICAL ANOREXIC IS A MODEL TEENAGER WHO IS
OBSESSED WITH FOOD—BUYING, COOKING, AND
PREPARING IT—BUT WHO EATS VERY LITTLE HERSELF.
 BULIMIA NERVOSA, A DISORDER THAT FOLLOWS A
PATTERN OF BINGE‐PURGE EATING. AFTER EATING AN
ENORMOUS AMOUNT OF FOOD, BULIMICS VOMIT,
TAKE LAXATIVES, OR EXERCISE VIGOROUSLY TO BURN
OFF RECENTLY CONSUMED CALORIES.
 ADOLESCENT DEPRESSION, OFTEN DUE TO
HORMONAL CHANGES, LIFE CHALLENGES, AND/OR
CONCERNS ABOUT APPEARANCE. MORE TEENAGE
FEMALES THAN MALES SUFFER FROM DEPRESSION.
SOME ADOLESCENTS ABUSE SUBSTANCES TO ESCAPE
THE PAINS OF GROWING UP, TO COPE WITH DAILY
STRESSES, OR TO BEFRIEND PEERS WHO ARE PART OF
A CROWD. AS ALLURING SYMBOLS OF ADULTHOOD,
ALCOHOL AND TOBACCO/NICOTINE ARE THE EASILY
AVAILABLE DRUGS OF CHOICE FOR ADOLESCENTS.
This Photo by Unknown Author is licensed under CC BY-NC

14. EARLY ADULTHOOD (20 TO EARLY 40S)
BIOLOGICAL CHANGES:
BODY FULLY DEVELOPED BY EARLY TO MID 20S.
MUSCLE STRENGTH, REACTION TIME AND CARDIAC FUNCTIONING
WEIGHT GAIN AND BREASTS.
BRAIN CHANGES:
EARLY ADULTHOOD
FRONTAL LOBES OF THE CEREBRAL CORTEX
CAREER AND INDEPENDENCE
HEALTH CHANGE:
CHANGE IN VISION, SKIN AND SAGGING CHINS
EATING DISORDERS

15. MIDDLE ADULTHOOD (40S-
60S)BIOLOGICAL CHANGES:
AGING
LOSE HEIGHT AND GAIN WEIGHT
VERTEBRAE AND BODY FAT
WRINKLE AND SAG
AGING SPOTS
BRAIN CHANGES:
INTELLIGENCES PEAKED IN ADOLESCENCE
VOCABULARY SKILLS
CRYSTALLIZED INTELLIGENCE
JUGGLE RESPONSIBILITIES

16. MIDDLE ADULTHOOD (40S-
60S)
HEALTH CHANGES:
WEAR DOWN
SARCOPENIA
OBESITY
CARDIOVASCULAR DISEASE
HYPERTENSION
FERTILITY DECLINES
TESTOSTERONE DECLINE

17. LATE ADULTHOOD (60 AND
ON)
BIOLOGICAL CHANGES:
PHYSICAL DISABILITY
WRINKLES AND SPOTS
WEIGHT DROP
BRAIN CHANGES:
DEMENTIA OR ALZHEIMER’S
LESS LIKELY TO ASSIMILATE DATA
VASCULAR DEMENTIA

18. LATE
ADULTHOOD
(60 AND ON)
HEALTH
CHANGES:
HYPERTENSION
AND STROKE
BLOOD PRESSURE
WATER-SOLUBLE
B VITAMIN MAY
INCREASE DISEASE
IMMUNE SYSTEMS

19. DEATH
BIOLOGICAL CHANGES:
MUSCLES RELAX
ORGANS NO LONGER RECEIVE
OXYGENATED BLOOD
CARDIAC ARREST
ALGOR MORTIS
BRAIN CHANGES:
BRAIN CELLS ARE DEPENDENT
GLUTAMATE STIMULATES OTHER BRAIN
CELLS
HEALTH CHANGES:
CARDIOVASCULAR DISEASE

20. REFERENCES
FOR
CHILDHOOD/
ADOLESCENCE
https://www.cliffsnotes.com/study-
guides/psychology/development-psychology/physical-
cognitive-development-1745/physical-development-
age-1745
Santrock, J. W. (2018). A topical approach to life-span
development. New York, NY: McGraw-Hill Education.
https://www.allpsychologycareers.com/topics/early-
adulthood-development.html
http://www.horizonresearch.org/patient-
caregive/biological-changes-at-the-end-of-life/
https://www.verywellhealth.com/what-happens-to-my-
body-right-after-i-die-1132498